Intracellular pH and Catecholamine Synthesis in Cultured Bovine Adrenal Medullary Cells: Effect of Extracellular Na+ Removal

Abstract
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. Dibutyrylcyclic 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 med um. 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.

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