The effect of acetylcholine on inositol lipid metabolism and intracellular calcium concentrations in bovine anterior pituitary cells

Acetylcholine (ACh) increased the intracellular calcium concentration in bovine anterior pituitary cells. In the presence of the calcium channel antagonists verapamil (20 microM) or nitrendepine (1 microM) the increase in calcium was partially inhibited but showed both transient and sustained components. In the presence of EGTA (2.5 mM) only the transient component was observed. ACh also decreased inositol radioactivity in phosphatidylinositides and increased it in inositol phosphates. It is concluded that the increase in calcium caused by acetylcholine requires both the entry of external calcium and mobilisation of internal calcium. Replacement of external sodium by N-methyl-D-glucamine inhibited the rises in calcium and inositol phosphate labelling in response to ACh. Tetrodotoxin (3 microM) or ouabain (50 microM) did not affect either response to ACh. Verapamil did not affect the calcium rise induced by ACh in the absence of external sodium. The phorbol ester PMA (10 nM) caused a transient rise in calcium and inhibited the calcium rise caused by acetylcholine: it did not modify the effect of acetylcholine on inositol phosphates. The dependence of the stimulation of external calcium entry and inositol phosphate production on external sodium ions and protein kinase C is discussed.