Mechanisms of propofol action on ion currents in the myelinated axon of Xenopus laevis.

The effect of the intravenous anaesthetic, propofol (2,6-diisopropylphenol), was investigated on frog myelinated axons under voltage-clamp conditions. The effect, in the concentration range 60 microM to 10 mM, was a combination of (i) a negative shift of the steady state activation and inactivation curves for both Na+ and K+ currents (INa,IK), (ii) a voltage-independent block of INa, but not of IK, and (iii) a slowed time course of IK activation. The shift was dose-dependent and, at 1 mM, about -10 mV for the activation and -16 mV for the inactivation curves. The voltage-independent INa block showed 1:1 stoichiometry and 50% reduction at 2.7 mM. The slowed IK activation showed saturation at 1 mM with a doubled time to half steady state value. All the effects were only partially reversible and showed a complex time course at application and washing. The shift of potential dependence may be explained by a general effect on the membrane electric field. The findings suggest effects directly on channel proteins as well as on membrane lipids.