Regulation by monovalent cations of histamine H2 receptor-coupled adenylate cyclase from guinea pig fundic gastric mucosa

In thoroughly washed guinea pig fundic gastric mucosal membranes, NaCl markedly potentiates the maximal histamine-stimulated adenylate cyclase activity and increases the concentration of histamine required for half-maximal effect (EC₅₀). The apparent dissociation constants for the antagonists cimetidine and metiamide are only slightly increased in the presence of NaCl. Potassium chloride does not change the histamine EC₅₀ but does increase the maximal histamine-stimulated adenylate cyclase activity. These results suggest that Na and K ions may play an important role in the regulation of histamine-sensitive adenylate cyclase in gastric mucosa. The effect of the Na ion appears to be more specific for histamine H₂ receptor agonists than for antagonists.