Neurotransmitter-induced modulation of neuronal Ca current is not mediated by intracellular Ca2+ or cAMP.

Dopamine (1 microM) inhibits the Ca component of action potential and corresponding electroexcitable Ca current (ICa) in isolated snail neurons. Adrenaline and serotonin also reduce ICa. The inhibition is not related to changes in intracellular Ca2+ or cAMP concentrations: internal application of 10 mM ethyleneglycoltetraacetic acid or 10 microM cAMP in the mixture with 1 mM Mg-ATP and 2 mM theophylline does not influence the action of neurotransmitters on ICa.