British Journal of Anaesthesia, Vol 82, Issue 1 74-80, Copyright © 1999 by The Board of Management and Trustees of the British Journal of Anaesthesia
H. C. Wartenberg, B. W. Urban and D. S. Duch
Fast inactivation of sodium channel function is modified by anaesthetics.
Its quantitative contribution to the overall anaesthetic effect is assessed
by removing the fast inactivation mechanism enzymatically. Sodium channels
from human brain cortex were incorporated into planar lipid bilayers. After
incorporation, channels were exposed to increasing concentrations of
pentobarbital (pentobarbitone), either before or after fast inactivation
had been enzymatically removed using trypsin. Anaesthetic suppression of
these channels with or without the fast inactivation site was compared by
analysing single channel currents. Treatment with cytoplasmic trypsin
alleviated two-thirds of the pentobarbital block on open channel
probability (fractional channel open time). The hyperpolarizing shift in
steady-state activation caused by pentobarbital was not affected by
treatment with trypsin. Extracellular trypsin was ineffective. These
results support a model of general anaesthetic action on sodium channels in
which anaesthetics produce a concentration-dependent shift in the
distribution between activated and inactivated states towards fast
inactivation. Some pentobarbital effects remained after removal of
inactivation. The results support a multi-mechanistic model of anaesthetic
action on brain sodium channels.
LABORATORY INVESTIGATIONS
Distinct molecular sites of anaesthetic action: pentobarbital block of human brain sodium channels is alleviated by removal of fast inactivation
Department of Anesthesiology and Physiology, Cornell University Medical College, 1300 York Avenue, New York, NY 10021, USA; Present address: Klinik und Poliklinik fur Anasthesiologie und spezielle Intensivmedizin, Rheinishe Friedrich-Wilhelms-Universitat Bonn, Sigmund-Freud-Stase 25, D-53105 Bonn, Germany
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