An alpha 40 subunit of a GTP-binding protein immunologically related to Go mediates a dopamine-induced decrease of Ca2+ current in snail neurons.

Dopamine induces a decrease in voltage-dependent Ca2+ current in identified neurons of the snail H. aspersa. This effect is blocked by intracellular injection of activated B. pertussis toxin and of an affinity-purified antibody against the alpha subunit of bovine Go protein. The dopamine effect is mimicked by intracellular injection of mammalian alpha o. In snail nervous tissue, pertussis toxin ADP-ribosylates a single protein band on SDS gels, and this band is recognized in immunoblots by the anti-alpha o antibody. We propose that this is a 40 kd alpha subunit of a molluscan G protein immunologically related to alpha o and that it mediates the effect of dopamine on Ca2+ currents in identified snail neurons.