Modulation of calcium current in snail neurones by dopamine: the role of intracellular free calcium.

The inhibition of voltage-gated Ca-current in Limnaea stagnalis (L.) neurones by dopamine cannot be prevented by intracellular administration of the Ca-chelating agent, EGTA. At the same time, substitution of external Ba2+ for Ca2+ substantially weakens the dopamine-induced inhibition. The Ca-ionophore, A23187, also produces an inhibition, but the inhibitory effect of A23187 and of dopamine on Ca-current are non-additive. These findings allow one to suggest that the entry and increase of free Ca concentration presumably in the narrow submembrane space, but not in the bulk of cytoplasm, is important for development of inhibition of neuronal Ca-current by dopamine.