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 analyzin g the effects of halothane and propofol on the activation of purified rat brain PKC by its three essential activators, phosphatidylserine, d iacylglycerol, and Ca2+, each of which is known to interact with the r egulatory domain. Clinically relevant concentrations of halothane (2.4 vol%) and propofol (200 mu M) increased the V-max without affecting t he K-m for phosphorylation of the artificial substrate histone H1 by P KC, and increased the sensitivity of PKC to activation by phosphatidyl serine, diacylglycerol, and Ca2+. Halothane reduced the EC(50) 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) an d for free Ca2+ from 4.5 +/- 1.0 to 2.8 +/- 0.4 mu M (P < 0.05). Propo fol reduced the EC(50) values for phosphatidylserine from 18 +/- 1.9 t o 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 mu M (P < 0.05). The IC50 values for inhibition of PKC activity by the regulatory domain-specific PKC inhibitor sphingosine were incr eased from 20 +/- 1.5 to 26 +/- 0.6 mu M (P < 0.01) by halothane and f rom 24 +/- 4.8 to 34 +/- 4.8 mu M (P < 0.05) by propofol. These data s uggest that halothane and propofol stimulate brain PKC activity by sta bilizing its active conformation through an interaction with its regul atory domain. Given the diverse role of PKC in physiologic regulation, alterations in PKC activity may be a relevant mechanism for general a nesthetic effects.