Barbiturates increase the rate of voltage-dependent inactivation of the calcium current in snail neurones.

Effects of barbiturates (thiopentone, pentobarbitone, phenobarbitone and barbitone) on the calcium current (ICa) in identified Helix neurones were studied, using a conventional suction pipette technique. Barbiturates depressed the maximal peak amplitudes (MPA) of ICa in a dose-dependent manner without shifting the current-voltage relationships along the voltage axis. Barbiturates accelerated the decay phase of ICa at high concentrations (1 X 10(-4) to 3 X 10(-3) M), at which concentrations double-pulse experiments showed the increased rate of a voltage-dependent inactivation of ICa. It is concluded that the acceleration of the decay phase of ICa by barbiturates may be due to the increased rate of the voltage-dependent inactivation of ICa.