Differential requirements for Ca2+ concentrations for catecholamine release and biosynthesis in isolated bovine adrenal chromaffin cells

Differential effects of Ca²⁺] on catecholamine release and biosynthesis in isolated bovine adrenal chromaffin cells were investigated. Carbamylcholine, an agonist of the nicotinic and muscarinic acetylcholine receptor, or Na⁺ deprivation in the incubation medium, stimulated catecholamine release and biosynthesis in these cells. The concentrations of extracellular Ca²⁺] which stimulate catecholamine biosynthesis were less than those which stimulate catecholamine release. An increase in intracellular levels of free Ca²⁺ (Ca²⁺]_i) induced by Na⁺ deprivation was dependent on extracellular Ca²⁺]. These results indicate that, in bovine adrenal chromafn cells, catecholamine biosynthesis is regulated by lower levels of Ca²⁺]_i than is catecholamine release.