Failure of the calcium channel activator, Bay K 8644, to increase the release of acetylcholine from nerve terminals in brain and diaphragm.

The calcium channel activator Bay K 8644 did not increase the release of acetylcholine from rat brain cortex prisms incubated in the presence of 3 mmol l-1 or 25 mmol l-1 K+ nor from rat diaphragms incubated in the presence of 5 mmol l-1 or 25 mmol l-1 K+. It also did not influence the release of acetylcholine from cortex prisms incubated in the presence of 25 mmol l-1 K+ and of lowered concentrations of Ca2+ ions. It is concluded that the voltage-dependent Ca2+ channels in the nerve terminals, responsible for the depolarization-induced influx of Ca2+ ions into the nerve terminals and thus for the depolarization-evoked release of acetylcholine from the nerve terminals, are different from the voltage-dependent Ca2+ channels in the heart and smooth muscle cells.