Intracellular pH and catecholamine synthesis in cultured bovine adrenal medullary cells: effect of extracellular Na+ removal.

Incubation of cultured bovine adrenal medullary cells in Na+-free sucrose medium or in Na+-free Cs+ medium enhanced the synthesis of 14C-catecholamines from [14C]tyrosine about two- to threefold or sixfold, respectively. The increment of 14C-catecholamine synthesis produced by Na+-free medium was partially dependent on the presence of Ca2+ in the medium. Dibutyryl cyclic AMP also stimulated the synthesis of 14C-catecholamines in adrenal medullary cells, and the effects of Na+ removal and dibutyryl cyclic AMP (5 mM) on the synthesis were almost additive. The intracellular pH measured by using a weak acid 5,5-dimethyloxazolidine-2,4-dione was 7.14 in control cells and when Na+ was replaced by sucrose or Cs+, it shifted down to 6.56 or 5.66, respectively. The fall in intracellular pH and the stimulation of 14C-catecholamine synthesis were similarly dependent on the concentration of Na+ in the medium. The optimal pH of soluble tyrosine hydroxylase was 5.5-6.0 both in control cells and in cells incubated in Na+-free medium. These results suggest that removal of extracellular Na+ increases the synthesis of catecholamines, at least in part, by shifting the intracellular pH toward the optimal pH of tyrosine hydroxylase.