Protein kinase C co-expression and the effects of halothane on rat skeletal muscle sodium channels

1 Voltage-gated Na channels, which are potential targets for general anaest hetics, are substrates for PKC, which phosphorylates a conserved site in th e channel inactivation gate. We investigated the idea that PKC modulates th e effect of volatile anaesthetics on Na channels via phosphorylation of thi s inactivation gate site. 2 Na currents through rat skeletal muscle Na channel alpha-subunits express ed in Xenopus oocytes were measured by two-microelectrode voltage clamp in the presence of the volatile anaesthetic agent halothane (2-bromo-2-chloro- 1,1,1-trifluroethane). PKC activity was modulated by co-expression of a con stitutively active PKC alpha-isozyme. 3 Halothane (0.4 mM) had no effect on Na currents. With co-expression of PK C, however, halothane dose-dependently enhanced the rate of Na current deca y and caused a small, but statistically significant reduction in Na current amplitude. 4 The enhancement of Na current decay was absent in a Na channel mutant in which the inactivation gate phosphorylation site was disabled. Effects of h alothane on amplitude were independent of this mutation. 5 Co-expression of a PKC alpha-isozyme permits an effect of halothane to ha sten current decay and reduce current amplitude, at least in part through i nteraction with the inactivation gate phosphorylation site. We speculate th at the interaction between halothane and Na channels is direct, and facilit ated by PKC activity and by phosphorylation of a site in the channel inacti vation gate.