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

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Abstract
1 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. 2 Barbiturates depressed the maximal peak amplitudes (MPA) of ICa in a dose-dependent manner without shifting the current-voltage relationships along the voltage axis. 3 Barbiturates accelerated the decay phase of ICa at high concentrations (1 × 10−4 to 3 × 10−3 m), at which concentrations double-pulse experiments showed the increased rate of a voltage-dependent inactivation of ICa. 4 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.