BJA Advance Access originally published online on July 18, 2006
British Journal of Anaesthesia 2006 97(3):320-328; doi:10.1093/bja/ael179
Mg2+ dependence of Ca2+ release from the sarcoplasmic reticulum induced by sevoflurane or halothane in skeletal muscle from humans susceptible to malignant hyperthermia
1 Institute of Membrane and Systems Biology, University of Leeds Woodhouse Lane, Leeds LS2 9JT, UK.
2 Academic Unit of Anaesthesia, St James's University Hospital Leeds LS9 7TF, UK
*Corresponding author. E-mail d.steele{at}leeds.ac.uk
Accepted for publication May 2, 2006.
 |
Abstract |
|---|
 Top Abstract IntroductionMaterials and methodsResultsDiscussionConclusionsREFERENCES |
|---|
Background. In normal resting muscle, cytosolic Mg2+ exerts a potent inhibitory influence on the sarcoplasmic reticulum (SR) Ca2+ release channel (ryanodine receptor, RyR1). Impaired Mg2+-regulation of RyR1 has been proposed as a causal factor in malignant hyperthermia (MH). The aim of this study was to compare the effects of cytosolic Mg2+ on SR Ca2+ release induced by halothane or sevoflurane in normal (MHN) and MH susceptible (MHS) human skeletal muscle fibres.
Methods. Samples of vastus medialis muscle were obtained from patients under investigation for MH susceptibility. Single fibres were mechanically skinned and perfused with solutions mimicking the intracellular milieu. Changes in [Ca2+]i were detected using fura-2 fluorescence after application of equimolar halothane or sevoflurane.
Results. In MHN fibres, concentrations of sevoflurane or halothane as high as 10 mM typically failed to induce SR Ca2+ release at physiological free [Mg2+] (1 mM). However, when [Mg2+] was decreased to 0.4 mM, SR Ca2+ release occurred in 51% (16/33) and 6% (2/33) of MHN fibres after the addition of 1 mM halothane or 1 mM sevoflurane, respectively. Further decreases in [Mg2+] increased the proportion of responsive fibres. In the presence of 0.1 mM [Mg2+], Ca2+ release occurred in all fibres (33/33) after the introduction of 1 mM halothane or 1 mM sevoflurane. In MHS fibres, 1 mM halothane or 1 mM sevoflurane-induced Ca2+ release in 54% (7/13) or 15% (2/13) of fibres, respectively, at 1 mM Mg2+. A decrease in [Mg2+] to 0.2 mM Mg2+ was sufficient to render 100% of MHS fibres (13/13) responsive to 1 mM halothane or 1 mM sevoflurane.
Conclusions. In both MHS and MHN fibres (i) halothane is a more potent activator of SR Ca2+ release than sevoflurane and (ii) as with halothane, the efficacy of sevoflurane-induced SR Ca2+ release exhibits a marked dependence on cytosolic [Mg2+]. The marked potentiation of SR Ca2+ release after a moderate reduction in cytosolic [Mg2+] suggests that conditions which cause hypomagnesaemia will increase the probability and possibly severity of an MH event. Conversely, maintenance of a normal or slightly increased cytosolic [Mg2+] may reduce the probability of MH.
Keywords: anaesthetics volatile, sevoflurane; anaesthetics volatile, halothane; complications, malignant hyperthermia; Mg2+; muscle cardiac, sarcoplasm reticulum
|
Introduction |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionConclusionsREFERENCES |
|---|
Malignant hyperthermia (MH) is a pharmacogenetic condition triggered by exposure to volatile anaesthetics, which results in skeletal muscle contracture and a potentially fatal increase in body temperature.1 Defects in the RYR1 gene [the gene encoding the skeletal muscle sarcoplasmic reticulum (SR) Ca2+ release channel or ryanodine receptor, RyR1]. are known to be responsible for MH susceptibility in
50% of diagnosed families.2 3 Functional studies have shown that RYR1 mutations linked to MH result in RyR1 ‘hypersensitivity’, such that clinically relevant concentrations of volatile anaesthetics can induce Ca2+ release from the SR.4 5 In normal resting muscle, cytosolic Mg2+ exerts a potent inhibitory action on RyR1, which prevents regenerative Ca2+-induced Ca2+ release (CICR) and confers a low sensitivity to pharmacological agonists.6 However, experiments on isolated RyRs and SR vesicles have provided evidence that both human and porcine MH is associated with a decrease in the inhibitory action of cytosolic Mg2+ on RyR1.7 8 This conclusion is supported by studies on skinned fibres obtained from rat muscle, showing that the potency of halothane's action on RyR1 increases markedly when the free cytosolic [Mg2+] decreases below normal physiological concentrations.9 10 Furthermore, in human muscle, the characteristics of the halothane-induced Ca2+ release process in normal fibres (slow, diffuse, localized) can be transformed to the MH susceptible (MHS) phenotype (rapid, propagating, regenerative) by decreasing the free [Mg2+].5
This work suggests that a moderate reduction in the inhibitory action of cytosolic Mg2+ might explain the hypersensitivity of RyR1 to volatile anaesthetics, which is known to underlie most MH cases. Variability in intracellular [Mg2+] concentrations resulting from diet, disease or other genetic factors might also influence the probability or severity of an MH episode in susceptible patients. However, in previous studies, either caffeine or halothane was used to study the Mg2+-dependence of RyR1 activation.7–9 11 It is not clear whether these data can be extended to more commonly used volatile anaesthetics such as sevoflurane, where effects on SR Ca2+ regulation are less well characterized. The aim of this study was to compare directly the Mg2+-sensitivity of halothane and sevoflurane-induced Ca2+ release from the SR in MH normal (MHN) and MHS human skeletal muscle. Experiments were performed on mechanically skinned vastus medialis fibres prepared from biopsy samples obtained from patients undergoing MH diagnosis.
|
Materials and methods |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionConclusionsREFERENCES |
|---|
Solution composition
All chemicals were purchased from Sigma-Aldrich Ltd (Gillingham, Dorset, UK). The basic solution contained (mM): HEPES 25, EGTA 0.15, creatine phosphate 10, adenosine 5' triphosphate 5, KCl 100 and Fura-2 0.002. Creatine phosphate and adenosine 5' triphosphate were added as di-sodium salts. The free [Ca2+] of the basic solution was adjusted to 120 nM by addition of CaCl2. Free [Mg2+] was altered to 1.5, 1, 0.4, 0.2 and 0.1 mM by addition of MgCl2. The free and bound concentrations of ions in the experimental milieu were calculated as necessary using an in-house computer program. Experiments were performed at room temperature [22 (2)°C], pH 7.0. Halothane or sevoflurane was added from a stock solution prepared in dimethyl sulphoxide (DMSO). In experiments, where 1 mM halothane or sevoflurane was used, the DMSO concentration was 0.1%. When higher concentrations (5–40 mM) were applied, the maximum DMSO concentration did not exceed 2%. In control experiments, 2% DMSO did not induce release of Ca2+ from the SR, or modify other aspects of SR function (not shown). To prevent vaporization, the anaesthetic-containing solutions were kept in airtight syringes with zero dead space throughout all experiments. In previous studies, the stability of halothane and sevoflurane concentrations in similar delivery systems has been verified using gas liquid chromatography.12 13
Preparation
Samples of vastus medialis muscle were obtained by open biopsy from patients attending for MH susceptibility testing at St James's Hospital Leeds, UK. Approximately 1 g of muscle was removed for the in vitro contracture test (IVCT). With institutional Research Ethics Committee approval and informed patient consent, an additional bundle (0.2 g) was used to provide material for studies on mechanically skinned muscle preparations. All procedures were carried out according to the Declaration of Helsinki. The IVCT provided the primary method of categorizing MHN and MHS tissue, according to the criteria for MH research of the European MH Group.14 This ensures a high sensitivity and specificity of the MHS diagnosis (98 and 94%, respectively).15 Only one fibre was used per patient. Samples were obtained from a total of 46 patients (MHN, 33; MHS, 13).
The smaller bundle of muscle used to prepare skinned fibres was placed in a solution approximating to the intracellular milieu. Individual muscle fibres were isolated and then mechanically skinned with fine forceps. Vastus medialis is of mixed fibre type and strontium sensitivity tests were routinely carried out to classify the fibres as type 1 or type 2.16 It was found that most of the preparations did not generate significant tension at pSr 5.2, suggesting that the majority of selected fibres were type 2. Any preparations generating significant tension at pSr 5.2 were not used in this study.
Apparatus
The apparatus for simultaneous measurement of [Ca2+] and force from skinned muscle fibres is described in detail elsewhere.17 Briefly, a mechanically skinned muscle fibre was mounted in a shallow bath with a glass coverslip base. A cylindrical Perspex column (3 mm diameter) was lowered to within a few micrometres of the stainless steel tubes (200 µm diameter) used to attach the muscle. The volume of solution immediately below the column was 1.4 µl. Preparations were perfused by pumping solution at 0.8 ml min–1 via a narrow duct passing through the centre of the column. Caffeine, halothane or sevoflurane were applied using a syringe pump, which allowed each of eight channels to be controlled independently via a computer interface. The plastic syringes (5 ml), containing caffeine or halothane solutions, were connected via narrow cannulae to a series of injection ducts near the base of the column. The bath was placed on the stage of an S 200 Nikon Diaphot inverted microscope (Nikon UK Limited, Kingston upon Thames, Surrey, UK). The muscle fibre was viewed via x40 Fluor objective (Nikon CF Fluor, NA 0.75). In all experiments the preparation was alternately illuminated with light of wavelengths 340 and 380 nm at a frequency of 45 Hz using a spinning wheel spectrophotometer (Cairn Research Limited, Faversham, Kent, UK). Changes in the [Ca2+] were indicated by the ratio of light intensities emitted at >500 nm.
Application of caffeine, halothane or sevoflurane
In all protocols, introduction of halothane or sevoflurane was preceded by a series of responses induced by brief (500 ms) application of a solution containing 40 mM caffeine, but lacking Mg2+ (40 mM caffeine/zero Mg2+) at 4 min intervals. In control experiments, it was found that (i) application of 40 mM caffeine/zero Mg2+ for 500 ms produced a maximal Ca2+ release, i.e. a higher [caffeine] or more prolonged application did not increase the response and (ii) increasing the Ca2+ loading period beyond 4 min did not increase the response. This suggests that the SR Ca2+ content reaches a steady state within 4 min. The caffeine-induced fluorescence transients provide an index of the SR Ca2+ content and the consistency of the responses was used to gauge the viability of the preparation. Mg2+ was omitted from the caffeine solution because previous studies suggest that even high concentrations of caffeine do not fully activate the SR Ca2+ release mechanism unless [Mg2+] is reduced to submillimolar concentrations.6
When halothane or sevoflurane is rapidly applied for a brief period during perfusion, a higher concentration is required to induce a measurable Ca2+ release than when the anaesthetics are applied for a longer period (1–2 min) in the absence of perfusion.10 This occurs for the following reasons: first, during constant perfusion, Ca2+ released from the SR can diffuse from the skinned fibre into the surrounding medium. Consequently, even a large efflux of Ca2+ from the SR may be essentially undetectable if the efflux rate is very low. In contrast, when the flow is stopped, any Ca2+ released from the SR will accumulate in the limited volume of solution underneath the column, increasing the likelihood of detection. Second, in the absence of flow, any given efflux of Ca2+ from the SR will result in a larger local increase in [Ca2+] in the vicinity of the RyRs, which may induce positive feedback via CICR. In intact skeletal muscle cells, Ca2+ transport across the sarcolemma occurs at a slow rate. Hence, the conditions in the absence of perfusion mimic that of the intact cell more closely than does continuous perfusion.
Effects of halothane and sevoflurane in MHN muscle fibres in the presence of a physiological [Mg2+].Skinned fibres from MHN patients were perfused continuously with a weakly Ca2+-buffered solution containing 120 nM [Ca2+] and 1 mM [Mg2+]. A solution with 40 mM caffeine/zero Mg2+ was applied briefly at 4 min intervals, resulting in a series of reproducible Ca2+ transients. After the last caffeine response, the preparation was perfused for a further 4 min to allow the SR to re-accumulate Ca2+. The solution was then rapidly exchanged for one containing 1 mM Mg2+/5 mM halothane or sevoflurane and perfusion stopped (see above). This protocol was repeated with 10, 20 and 40 mM of the anaesthetic.
Effects of cytosolic [Mg2+] on the sensitivity to 1 mM halothane or sevoflurane. Experiments were carried out on fibres from MHS and MHN patients to investigate the influence of halothane or sevoflurane on SR Ca2+ release after a decrease in the cytosolic [Mg2+]. After a series of control responses the preparation was perfused for a further 4 min to allow the SR to re-accumulate Ca2+. Perfusion was then stopped and the solution rapidly exchanged for one containing 1 mM Mg2+/1 mM anaesthetic. This protocol was repeated in the same preparation, but with other concentrations of Mg2+ (1.5, 0.4, 0.2 or 0.1 mM) present in the solution containing 1 mM anaesthetic.
Data recording and analysis
In all experiments, the ratio and individual wavelength intensity signals were low-pass filtered (3 db at 30 Hz) and digitized for later analysis using a personal computer with a Data Translation (Basingstoke, Hants, UK) 2801A card.
The effects of halothane and sevoflurane on MHN fibres in the presence of physiological [Mg2+] were analysed by comparing the numbers of fibres responding to the two anaesthetics applied at each concentration using Fisher's exact probability test using SPSS for Windows v9.0 (SPSS Inc., Chicago, IL). A P-value <0.01 was considered significant because of multiple comparisons.
The concentration of Mg2+ required to inhibit 1 mM halothane or sevoflurane-induced Ca2+ release in 50% of fibres (IC50) was estimated for MHN and MHS muscle. These estimates were derived from cumulative quantal dose–response curves fitted to the data using the standard four-parameter non-linear regression dose–response fitting function of SigmaPlot for Windows v8.0 (SPSS Inc., Chicago, IL). To obtain lower and upper 95% confidence limits for these IC50 estimates further dose–response curves were fitted to exact 95% confidence limits18 for the proportions of fibres not responding to the anaesthetic at each concentration of Mg2+.
|
Results |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionConclusionsREFERENCES |
|---|
Effects of halothane and sevoflurane in MHN muscle fibres in the presence of a physiological [Mg2+]
Figure 1A demonstrates the responses of single skinned MHN fibres to halothane (upper) or sevoflurane (lower). The figure shows two of the reproducible control Ca2+ transients after brief exposure to a solution containing 40 mM caffeine/zero Mg2+ followed by the responses to successive application of solutions containing 1 mM Mg2+ and 5, 10, 20 or 40 mM of the anaesthetic. Exposure to 5 or 10 mM halothane consistently failed to induce Ca2+ release. However, in this example, introduction of 20 mM halothane resulted in a slow sustained increase in [Ca2+] within the fibre. A further increase to 40 mM halothane induced a larger and more rapid response, which peaked at approximately the same amplitude as the preceding caffeine-induced transients, before declining towards a new steady state [Ca2+]. In the responses illustrated in Figure 1A, sevoflurane failed to induce Ca2+ release at 5, 10 or 20 mM. However, a small, slow increase in [Ca2+] did occur in the presence of 40 mM sevoflurane. As in previous studies,10 Ca2+ efflux was completely abolished by earlier exposure to ruthenium red, indicating that release occurs via the RyR (not shown).
|
Figure 1B shows cumulative data obtained using the same protocol. A significant increase in [Ca2+] was defined as >10% of the preceding caffeine-induced responses. The concentrations of both anaesthetics required to induce SR Ca2+ release were markedly above the maximum blood concentration achieved during anaesthetic maintenance or induction.19 20 However, significantly more fibres responded to halothane compared with sevoflurane at both 20 mM (P=0.008, Fisher's exact test) and 40 mM (P<0.001, Fisher's exact test).
Effects of cytosolic [Mg2+] on the sensitivity to 1 mm halothane or sevoflurane
Figures 2 and 3 illustrate examples of MHN and MHS fibres respectively exposed to 1 mM halothane or sevoflurane first applied in a solution containing 1 mM Mg2+ and then in a solution containing 0.4 mM Mg2+. In the MHN fibre, 1 mM halothane (Fig. 2A) consistently failed to induce Ca2+ release in the presence of 1 mM Mg2+. However, at 0.4 mM Mg2+, 1 mM halothane induced a substantial release of Ca2+ from the SR. The response exhibited an initial slow increase in [Ca2+] followed by a more rapid transient phase. Sevoflurane failed to induce Ca2+ release in the MHN fibre in the presence of 1 or 0.4 mM Mg2+ (Fig. 2B).
|
|
In the MHS fibre used in Figure 3, 1 mM halothane induced a slow increase in [Ca2+] followed by a more rapid phase which repeated cyclically in the presence of 1 mM Mg2+ (Fig. 3A). When the [Mg2+] was reduced to 0.4 mM, the response to halothane was more rapid in onset and was increased slightly in amplitude. In this example, sevoflurane failed to induce a significant release of Ca2+ from the SR in the presence of 1 mM Mg2+ (Fig. 3B). However, when the [Mg2+] was decreased to 0.4 mM, sevoflurane induced an initial slow increase in [Ca2+], followed by a rapid increase before declining to a new higher resting concentration.
Accumulated data illustrating the Mg2+-dependence of sevoflurane or halothane-induced SR Ca2+ release in MHN and MHS fibres are given in Figure 4. In MHN fibres, both sevoflurane and halothane consistently failed to induce Ca2+ release from the SR in the presence of 1 mM Mg2+. Decreasing the [Mg2+] to 0.4 mM resulted in a positive response to halothane in 51% (16/33) of fibres, while only 6% (2/33) responded to sevoflurane. In the presence of 0.2 mM Mg2+ all fibres responded to halothane and 52% (17/33) responded to sevoflurane. A further decrease in [Mg2+] to 0.1 mM was sufficient to render 100% (33/33) of the fibres responsive to both sevoflurane and halothane. The accumulated data also include results from experiments in which the [Mg2+] was increased to a supranormal concentration of 1.5 mM. Increasing the [Mg2+] reduced the proportion of MHS fibres which responded positively to 1 mM halothane and prevented sevoflurane-induced Ca2+ release in all preparations tested. The IC50 (95% CI) values for the effect of Mg2+ on anaesthetic-induced Ca2+ release indicate that halothane is a more potent activator of RyRs than sevoflurane in MHS muscle, IC50 (95% CI) 0.98 (0.96–1.03) mM vs 0.41 (0.37–0.85) mM, respectively, and in MHN muscle, IC50 (95% CI) 0.4 (0.39–0.41) mM vs 0.2 (0.19–0.23) mM, respectively.
|
|
Discussion |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionConclusionsREFERENCES |
|---|
In this study, concentrations of halothane or sevoflurane
10 mM failed to induce Ca2+ release from the SR in MHN fibres, at a physiological free [Mg2+] of 1 mM. However, when [Mg2+] was decreased to 0.4 mM, 1 mM halothane or 1 mM sevoflurane activated SR Ca2+ release in 51% (16/33) and 6% (2/33) of MHN fibres, respectively. Further decreases in [Mg2+] increased the proportion of responsive MHN fibres; at 0.1 mM [Mg2+] all fibres responded positively to 1 mM sevoflurane or 1 mM halothane. In MHS fibres, introduction of 1 mM halothane or 1 mM sevoflurane-induced Ca2+ release in 53% (7/13) and 15% (2/13) of fibres, respectively, in the presence of 1 mM Mg2+ (Fig. 3). Stepwise decreases in [Mg2+] also increased the proportion of responsive MHS fibres. A decrease in [Mg2+] to 0.2 mM Mg2+ was sufficient to render 100% of MHS fibres responsive to either 1 mM halothane or 1 mM sevoflurane. In MHS fibres, increasing the [Mg2+] to 1.5 mM reduced the proportion of fibres which responded positively to 1 mM halothane and was sufficient to prevent SR Ca2+ release in response to 1 mM sevoflurane in all fibres.
Comparative effects of halothane and sevoflurane
Consistent with previous studies, sevoflurane was found to be a less potent activator of RyR1 than halothane.21 This may underlie clinical (Hopkins PM, Halsall PJ, unpublished data presented at the 24th Annual Meeting of the European MH Group, Mainz, Germany, May 2005) and IVCT22 23 findings that sevoflurane is a less potent activator of MH than halothane. We have previously reported a marked Mg2+-dependence of halothane's action on the SR Ca2+ release mechanism in rat and human skeletal muscle.5 10 This study shows that sevoflurane-induced SR Ca2+ release is also highly dependent upon the cytosolic [Mg2+]. Furthermore, the characteristics of sevoflurane and halothane-induced Ca2+ release also appear qualitatively similar: with both anaesthetics, a slow increase in [Ca2+] was followed by a more rapid release phase, which often repeated cyclically, resulting in a maintained increase in [Ca2+]. Previous work using confocal microscopy has shown that this form of Ca2+ release takes the form of a propagating Ca2+ wave, mediated via regenerative CICR.5 This is an important observation, because propagating CICR does not occur in normal muscle because of the potent inhibition of RyR1 by cytosolic Mg2+.6 In MHS fibres, the ability of volatile anaesthetics to initiate propagating Ca2+ waves in the presence of a physiological cytosolic [Mg2+] suggests that the intrinsic inhibitory action of Mg2+ is reduced. The ability to induce similar responses in MHN fibres by reducing the cytosolic [Mg2+] is also consistent with this hypothesis.
Possible clinical relevance
Before considering the clinical implications of the study, it is appropriate to acknowledge the limitations of the experimental model. First, this study was performed at room temperature, while MH (and the IVCT) occurs at or near 37°C. While there is no evidence that the response of RyR1 to volatile anaesthetics changes qualitatively at lower temperatures, the sensitivity to activation may be lower. Second, in this study we have compared equimolar concentrations of sevoflurane and halothane. Comparison of equivalent MAC concentrations was not attempted because the anaesthetic concentration in the SR during anaesthesia and its proportion to the MAC have not been described and remain open to question, because lipid solubility is likely to be important. Despite these limitations, it is possible to draw qualitative conclusions regarding the possible clinical relevance of the present findings.
The maximum concentration of volatile anaesthetic in blood during clinical anaesthesia is unlikely to exceed three times the MAC50 value, which for both halothane and sevoflurane is 1 mM.19 20 24 However, in MHN fibres, concentrations of sevoflurane or halothane as high as 10 mM failed to induce Ca2+ release from the SR at a physiological free [Mg2+] (1 mM). This suggests that in MHN fibres, potent inhibition of RyR1 by cytosolic Mg2+ provides a considerable ‘safety factor’, such that clinically relevant concentrations of halothane or sevoflurane cannot directly activate SR Ca2+ release. However, relatively small deviations above or below the physiological [Mg2+] have a marked influence on the sensitivity of RyRs to halothane or sevoflurane in both MHN and MHS muscle (Fig. 4).
While the existing evidence suggests that RyR1 mutations underlie a high proportion of MH cases, there is considerable variation in clinical outcome, e.g. proven MHS patients are known to have had uneventful exposure to triggering anaesthetics before developing signs on subsequent exposure.25 This suggests that other factors may affect the responsiveness of RyR1 mutations to volatile anaesthetics. Based on the present data, variations in cytosolic [Mg2+] would be expected to have a considerable influence on the probability of developing MH. Under normal physiological conditions most cellular Mg2+ is bound to ATP. Given the affinity constants for Mg2+ binding to ATP, it can be calculated that a 15% decrease in total Mg2+ would be sufficient to increase markedly the likelihood of MH developing.
It has been shown that MH-susceptible patients exhibit a greater variability in skeletal muscle [Mg2+] concentrations than control subjects, leading to the suggestion that unknown genetic factors associated with the disease may influence [Mg2+] regulation.26 Furthermore, conditions such as diabetes,27 heart failure,28 asthma29 or treatment with diuretics30 have been shown to result in reduced plasma and cellular [Mg2+]. Severe hypomagnesaemia and intracellular skeletal muscle Mg2+ depletion has been reported after treatment with the cancer therapy drug cisplatin.31 Conversely, Mg2+ concentrations can increase in renal failure32 or after infusion of magnesium sulphate during operative procedures,33 which might be expected to reduce the probability of an MH episode.
Our study suggests that maintenance of normal or slightly raised intracellular Mg2+ concentrations may have benefits for some patients undergoing anaesthesia. However, although long-term dietary Mg2+ supplementation can restore Mg2+ concentrations in deficient subjects,34 it is uncertain whether similar effects can be achieved by an acute increase in plasma [Mg2+] during or before anaesthesia. Previous work on MH-susceptible pigs has shown that earlier infusion of magnesium sulphate (100 mg kg–1) attenuated the increase in [Ca2+]i and the associated limb rigidity that would normally have occurred on introduction of 2% halothane.35 However, in this case, the beneficial effects of Mg2+ may have occurred via an extracellular action as transport across the sarcolemma appears to occur at a relatively slow rate.36 Further work is required to establish the potential benefits of Mg2+ supplementation in relation to anaesthesia.
|
Conclusions |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionConclusionsREFERENCES |
|---|
The present data show that in both MHS and MHN fibres (i) halothane is a more potent activator of SR Ca2+ release than sevoflurane and (ii) the efficacy of both halothane and sevoflurane to induce SR Ca2+ release exhibits a strong dependence on cytosolic [Mg2+]. The ability of both halothane and sevoflurane to induce SR Ca2+ release in MHS fibres in the presence of normal [Mg2+] and the marked potentiation of this effect by reduced [Mg2+] suggests that conditions or interventions resulting in hypomagnesaemia will increase the probability of an MH event. Conversely, maintenance of a normal or slightly increased concentration of cytosolic [Mg2+] may reduce the probability of MH.
|
Acknowledgments |
|---|
The financial support of The Wellcome Trust is acknowledged.
|
REFERENCES |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionConclusionsREFERENCES |
|---|
1 Mickelson JR and Louis CF. Malignant hyperthermia: excitation–contraction coupling, Ca2+ release channel, and cell Ca2+ regulation defects. Physiol Rev 1996; 76:537–92
2 Sambuughin N, Sei Y, Gallagher KL, et al. North American malignant hyperthermia population: screening of the ryanodine receptor gene, identification of novel mutations. Anesthesiology 2001; 95:594–9[CrossRef][Web of Science][Medline]
3 Robinson RL, Anetseder MJ, Brancadoro V, et al. Recent advances in the diagnosis of malignant hyperthermia susceptibility: how confident can we be of genetic testing? Eur J Hum Genet 2003; 11:342–8[CrossRef][Web of Science][Medline]
4 Tong J, Oyamada H, Demaurex N, Grinstein S, McCarthy TV, MacLennan DH. Caffeine and halothane sensitivity of intracellular Ca2+ release is altered by 15 calcium release channel (ryanodine receptor) mutations associated with malignant hyperthermia and/or central core disease. J Biol Chem 1997; 272:26332–9
5 Duke AM, Hopkins PM, Halsal JP, Steele DS. Mg2+ dependence of halothane-induced Ca2+ release from the sarcoplasmic reticulum in skeletal muscle from humans susceptible to malignant hyperthermia. Anesthesiology 2004; 101:1339–46[Web of Science][Medline]
6 Lamb GD, Cellini MA, Stephenson DG. Different Ca2+ releasing action of caffeine and depolarisation in skeletal muscle fibres of the rat. J Physiol 2001; 531:715–28
7 Laver DR, Owen VJ, Junankar PR, Taske NL, Dulhunty AF, Lamb GD. Reduced inhibitory effect of Mg2+ on ryanodine receptor-Ca2+ release channels in malignant hyperthermia. Biophys J 1997; 73:1913–24[Web of Science][Medline]
8 Yang T, Ta TA, Pessah IN, Allen PD. Functional defects in six ryanodine receptor isoform-1 (RyR1) mutations associated with malignant hyperthermia and their impact on skeletal excitation-contraction coupling. J Biol Chem 2003; 278:25722–30
9 Duke AM, Hopkins PM, Steele DS. Effects of Mg2+ and SR luminal Ca2+ on caffeine-induced Ca2+ release in skeletal muscle from humans susceptible to malignant hyperthermia. J Physiol 2002; 544:85–95
10 Duke AM, Hopkins PM, Steele DS. Mg2+ dependence of halothane-induced Ca2+ release from the sarcoplasmic reticulum in rat skeletal muscle. J Physiol 2003; 551:447–54
11 Owen VJ, Taske NL, Lamb GD. Reduced Mg2+ inhibition of Ca2+ release in muscle fibres of pigs susceptible to malignant hyperthermia. Am J Physiol 1997; 272:203–11
12 Harrison SM, Robinson M, Davies LA, Hopkins PM, Boyett MR. Mechanisms underlying the inotropic action of halothane on intact rat ventricular myocytes. Br J Anaesth 1999; 82:609–21
13 Graham MD, Bru-Mercier G, Hopkins PM, Harrison SM. Transient and sustained changes in myofilament sensitivity to Ca2+ contribute to the inotropic effects of sevoflurane in rat ventricle. Br J Anaesth 2005; 94:279–86
14 The European Malignant Hyperpyrexia Group. A protocol for the investigation of malignant hyperpyrexia (MH) susceptibility. Br J Anaesth 1984; 56:1267–9
15 Ording H, Brancadoro V, Cozzolino S, et al. In vitro contracture test for diagnosis of malignant hyperthermia following the protocol of the European MH Group: results of testing patients surviving fulminant MH and unrelated low-risk subjects. The European Malignant Hyperthermia Group. Acta Anaesthesiol Scand 1997; 41:955–66[Web of Science][Medline]
16 Fink RH, Stephenson DG, Williams DA. Physiological properties of skinned fibres from normal and dystrophic (Duchenne) human muscle activated by Ca2+ and Sr2+. J Physiol 1990; 420:337–53
17 Duke AM and Steele DS. Effects of cyclopiazonic acid on Ca2+ regulation by the sarcoplasmic reticulum in saponin permeabilized skeletal muscle fibres. Pflugers Arch 1998; 436:104–11[CrossRef][Web of Science][Medline]
18 Diem K and Lentner C. Scientific Tables 1970. 7th Edn Macclesfield Geigy Pharmaceuticals pp. 85–6
19 Franks NP and Lieb WR. Temperature dependence of the potency of volatile general anesthetics: implications for in vitro experiments. Anesthesiology 1996; 84:716–20[CrossRef][Web of Science][Medline]
20 Davies DN, Steward A, Allott PR, Mapleson WW. A comparison of arterial and arterialized venous concentrations of halothane. Br J Anaesth 1972; 44:548–50
21 Kunst G, Graf BM, Schreiner R, Martin E, Fink RH. Differential effects of sevoflurane, isoflurane, and halothane on Ca2+ release from the sarcoplasmic reticulum of skeletal muscle. Anesthesiology 1999; 91:179–86[CrossRef][Web of Science][Medline]
22 Snoeck MM, Gielen MJ, Tangerman A, van Egmond J, Dirksen R. Contractures in skeletal muscle of malignant hyperthermia susceptible patients after in vitro exposure to sevoflurane. Acta Anaesthesiol Scand 2000; 44:334–7[CrossRef][Web of Science][Medline]
23 Hopkins P and Halsall JP. In vitro skeletal muscle contracture responses to sevoflurane—a potential diagnostic test for malignant hyperthermia susceptibility? Br J Anaesth 2004; 92:311P–2P
24 Eckenhoff RG and Johansson JS. On the relevance of ‘clinically relevant concentrations’ of inhaled anesthetics in in vitro experiments. Anesthesiology 1999; 91:856–60[CrossRef][Web of Science][Medline]
25 Strazis KP and Fox AW. Malignant hyperthermia: a review of published cases. Anesth Analg 1993; 77:297–304[Web of Science][Medline]
26 Nelson TE, Flewellen EH, Belt MW, Kennamer DL, Winsett OE, Bee DE. Calcium and magnesium content of skeletal muscle. Studies in subjects undergoing diagnostic testing for malignant hyperthermia. Br J Anaesth 1987; 59:730–4
27 Nadler JL, Malayan S, Luong H, Shaw S, Natarajan RD, Rude RK. Intracellular free magnesium deficiency plays a key role in increased platelet reactivity in type II diabetes mellitus. Diabetes Care 1992; 15:835–41[Abstract]
28 Haigney MC, Wei S, Kaab S, et al. Loss of cardiac magnesium in experimental heart failure prolongs and destabilizes repolarization in dogs. J Am Coll Cardiol 1998; 31:701–6
29 Gustafson T, Boman K, Rosenhall L, Sandstrom T, Wester PO. Skeletal muscle magnesium and potassium in asthmatics treated with oral beta 2-agonists. Eur Respir J 1996; 9:237–40[Abstract]
30 Dorup I. Effects of K+, Mg2+ deficiency and adrenal steroids on Na+, K+-pump concentration in skeletal muscle. Acta Physiol Scand 1996; 156:305–11[CrossRef][Web of Science][Medline]
31 Lajer H, Bundgaard H, Secher NH, Hansen HH, Kjeldsen K, Daugaard G. Severe intracellular magnesium and potassium depletion in patients after treatment with cisplatin. Br J Cancer 2003; 89:1633–7
32 Rodman JS. Hypermagnesemia and progression of renal failure. Clin Nephrol 1986; 26:314[Web of Science][Medline]
33 Dorman BH, Sade RM, Burnette JS, et al. Magnesium supplementation in the prevention of arrhythmias in pediatric patients undergoing surgery for congenital heart defects. Am Heart J 2000; 139:522–8[CrossRef][Web of Science][Medline]
34 Paolisso G, Passariello N, Pizza G, et al. Dietary magnesium supplements improve B-cell response to glucose and arginine in elderly non-insulin dependent diabetic subjects. Acta Endocrinol (Copenh) 1989; 121:16–20
35 Lopez JR, Sanchez V, Lopez I, et al. The effects of extracellular magnesium on myoplasmic [Ca2+] in malignant hyperthermia susceptible swine. Anesthesiology 1990; 73:109–17[Web of Science][Medline]
36 Konishi M, Suda N, Kurihara S. Fluorescence signals from the Mg2+/Ca2+ indicator furaptra in frog skeletal muscle fibers. Biophys J 1993; 64:223–39[Web of Science][Medline]
CiteULike 
Connotea 
Del.icio.us What's this?
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||