Biochemical characterization of the stimulatory effects of halothane and propofol on purified brain protein kinase C.

Halothane and propofol stimulate activation of protein kinase C (PKC) in the presence of physiologically relevant lipid bilayer vesicles in vitro. The mechanism of this stimulation was characterized by analyzing the effects of halothane and propofol on the activation of purified rat brain PKC by its three essential activators, phosphatidylserine, diacylglycerol, and Ca2+, each of which is known to interact with the regulatory domain. Clinically relevant concentrations of halothane (2.4 vol%) and propofol (200 microM) increased the Vmax without affecting the Km for phosphorylation of the artificial substrate histone H1 by PKC, and increased the sensitivity of PKC to activation by phosphatidylserine, diacylglycerol, and Ca2+. Halothane reduced the EC50 values for phosphatidylserine from 18 +/- 2.5 to 11 +/- 0.6 mol% (P < 0.05), for diacylglycerol from 1.6 +/- 0.3 to 0.87 +/- 0.2 mol% (P < 0.05) and for free Ca2+ from 4.5 +/- 1.0 to 2.8 +/- 0.4 microM (P < 0.05). Propofol reduced the EC50 values for phosphatidylserine from 18 +/- 1.9 to 11 +/- 1.2 mol% (P < 0.01), for diacylglycerol from 2.5 +/- 0.3 to 1.2 +/- 0.4 mol% (P < 0.01) and for free Ca2+ from 2.8 +/- 0.7 to 1.9 +/- 0.2 microM (P < 0.05). The IC50 values for inhibition of PKC activity by the regulatory domain-specific PKC inhibitor sphingosine were increased from 20 +/- 1.5 to 26 +/- 0.6 microM (P < 0.01) by halothane and from 24 +/- 4.8 to 34 +/- 4.8 microM (P < 0.05) by propofol.(ABSTRACT TRUNCATED AT 250 WORDS)