Specificities of cholinergic receptors for the accumulation of inositol trisphosphates (InsP3) and cyclic GMP and mobilization of intracellular Ca2+ in relation to culture periods were investigated in primary cultures of bovine adrenal chromaffin cells. At 0.5 day in culture, muscarine, a specific agonist for muscarinic receptors, caused a greater effect on intracellular Ca2+ mobilization and the accumulation of Ins(1,3,4)P3 than did the nicotinic-specific agonist nicotine. On the contrary, at 5 days, nicotine produced a greater effect on the accumulation of Ins(1,3,4)P3 and intracellular calcium mobilization than did muscarine. Furthermore, at 0.5 day, the muscarinic antagonist atropine strongly inhibited the increase in InsP3 accumulation that was induced by the nonspecific agonist carbachol, whereas at 5 days the inhibitory effect of atropine was greatly lowered. On the other hand, the nicotinic receptor antagonists hexamethonium and d-tubocurarine showed a much higher inhibitory potency at 5 days compared with 0.5 day in culture. Cholinergic receptor subtypes involved in cyclic GMP accumulation showed functional shifts similar to those in InsP3 formation. Binding experiments with a muscarinic ligand excluded the possibility that the reduction in muscarinic effects on InsP3 and cyclic GMP formation and intracellular Ca2+ mobilization were due to disappearance of the muscarinic receptor itself. These data show that cholinergic receptors linked to the accumulation of InsP3 and cyclic GMP and Ca2+ mobilization functionally shift from muscarinic to nicotinic during primary culture of adrenal chromaffin cells.
