British Journal of Anaesthesia, Vol 77, Issue 4 508-516, Copyright © 1996 by The Board of Management and Trustees of the British Journal of Anaesthesia
F. Sakai, M. Hiraoka and K. Amaha
We have examined the effects of propofol and thiopentone on membrane
potentials and currents of isolated guineapig ventricular myocytes using
the whole-cell patch-clamp technique. After current clamping, propofol at
concentrations greater than 0.5 microgramsmol litre-1 shortened the plateau
and action potential duration (APD) (P < 0.05). Thiopentone 10
microgramsmol litre-1 prolonged APD (P < 0.05), whereas concentrations
of 50 microgramsmol litre-1 or higher decreased plateau height (P <
0.05) and resting membrane potential (RMP) (P < 0.05) with abbreviation
of the prolonged APD. With voltage clamping, propofol 1 microgramsmol
litre-1 decreased the L- type Ca2+ current (ICa,L) to 88.4% of control (P
< 0.01) without affecting the delayed rectifier K+ current (IK) and
propofol 10 microgramsmol litre-1 decreased ICa,L and IK to 75.0% (P <
0.01) and 78.4% (P < 0.01), respectively, with no effect on the inward
rectifier K+ current (IK1). Thiopentone 10 microgramsmol litre-1 decreased
ICa,L to 88.5% (P < 0.01) and IK to 78.3% (P < 0.05), while
thiopentone 100 microgramsmol litre-1 depressed ICa,L to 82.8% (P <
0.01), IK to 27.0% (P < 0.01) and IK1 to 67.3% (P < 0.05). These
results indicated that propofol, at concentrations greater than those that
are clinically relevant, shortened APD mainly by suppression of ICa,L, and
the biphasic effects on APD by thiopentone were caused by depression of IK,
and concomitant suppression of ICa,L and IK1 at higher concentrations. The
distinct cardiodepressant effects of propofol and thiopentone may be, at
least in part, attributed to different actions on membrane Ca2+ and K+
currents.
LABORATORY INVESTIGATIONS
Comparative actions of propofol and thiopentone on cell membranes of isolated guineapig ventricular myocytes
Department of Anaesthesiology and Critical Care Medicine, Tokyo Medical and Dental University, 1-5-45, Yushima, Bunkyo-ku, Toyko 113, Japan; Department of Cardiovascular Disease, Medical Research Institute, Tokyo Medical and Dental University, 1-5-45, Yushima, Bunkyo-ku, Toyko 113, Japan
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