GTP-dependent anion-sensitive adenylate cyclase in snail ganglia potentiation of neurotransmitter effects

Abstract

Snail ganglia possess an anion-sensitive adenylate cyclase. This enzyme was stimulated 100% by chloride in a strictly GTP-dependent manner. The apparent affinity of chloride for adenylate cyclase was 2 X 10(-4) M. Halogens were found to be the most active anions. Some inorganic anions such as SO4(2-) and H2PO4- were inactive, as were all the organic anions tested. Stimulation was not cumulative for any maximal concentration of the active anions except fluoride. Chloride potentiated the effect of fluoride, indicating that the anion effect is not fluoride-like. Another striking result is that chloride enhanced adenylate cyclase sensitivity to the neurotransmitters serotonin and dopamine. The absence of chloride stimulation when Mg2+ was replaced by Mn2+ further indicates a role of the GTP-binding protein (the G/F unit). Chloride could reversibly stimulate the adenylate cyclase activity already maximally stimulated by guanyl 5'-imidodiphosphate. We therefore suggest that, in snail ganglia, chloride raises the activity of the G/F unit-catalytic unit complex at some stage after its formation. The same specific anion-sensitive adenylate cyclase was also found in some of the rat tissues tested.