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Effects of halothane and propofol on purified brain protein kinase C activation
1Department of Anesthesiology, Cornell University Medical College, New York, New York 10021.
Background:
Protein kinase C (PKC) has been implicated as a target for general anesthetic action in the central nervous system. Previous reports have described either stimulation or inhibition of PKC activity by general anesthetics. This study examines the effects of halothane and propofol on the activity of purified rat brain PKC under various assay conditions.
Methods:
PKC was assayed in vitro using three previously characterized artificial substrates and three different lipid preparations in the absence or presence of halothane or propofol.
Results:
Both halothane (50% effective concentration = 2.2 vol%) and propofol (50% effective concentration = 240 microM) markedly stimulated histone H1 phosphorylation by PKC in the presence of a lipid vesicle preparation consisting of phosphatidylcholine, phosphatidylserine, and diacylglycerol. Less marked or no stimulation of PKC by both anesthetics was observed in the presence of a phosphatidylserine/diacylglycerol dispersion or using protamine or poly(lysine, serine) as substrate. Neither anesthetic significantly stimulated PKC activity in the presence of phosphatidylserine/diacylglycerol/Triton X-100 mixed micelles using histone H1, protamine or poly(lysine, serine) as substrate. Slight inhibition of PKC activity by halothane was observed under specific assay conditions with protamine as substrate. The activity of the catalytic fragment of PKC or of two lipid-independent second messenger-regulated protein kinases with conserved catalytic domains was not significantly affected by halothane.
Conclusions:
Both halothane and propofol stimulated purified brain PKC activity in vitro assayed with physiologically relevant lipid bilayers in the absence or presence of Ca2+. This effect appears to be mediated through the lipid-binding regulatory domain of PKC. The potencies of halothane and propofol in stimulating PKC in vitro are consistent with submaximal activation of PKC at clinically effective anesthetic concentrations, the pharmacologic significance of this effect requires confirmation in an intact cellular system.