Differences in the actions of organic and inorganic Ca2+-antagonists on the inactivation of the Ca2+ channel in a molluscan neurone.

The actions of organic and inorganic Ca2+-antagonists on an inactivation of the Ca2+ channel was studied in molluscan neurones using a suction pipette technique. Both Ca2+-antagonists decreased the peak amplitude of Ca2+ current (ICa). The organic Ca2+-antagonists verapamil and diltiazem hastened the decay of ICa, while the inorganic Ca2+-antagonists Co2+ and Cd2+ delayed it. The difference in the action of the Ca2+-antagonists on the decay of ICa may result from the different effects of the agents on a voltage-dependent inactivation of the Ca2+ channel.