Intracellular pH and Catecholamine Secretion from Bovine Adrenal Chromaffin Cells

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Abstract
: To study the role of intracellular pH (pH1) in catecholamine secretion and the regulation of pHi in bovine chromaffin cells, the pH-sensitive fluorescent indicator [2′,7′-bis(carboxyethyl)-5(6)-carboxyfluorescein] was used to monitor the on-line changes in pHi. The pHi of chromaffin cells at resting state is ⋍7.2. The pH1 was manipulated first by incubation of the cells with NH4+, and then the solution was replaced with a NH4+-frce solution to induce acidification of the cytoplasm. The pH1 returned toward the basal pH value after acidification within 5–10 min in the presence of Na+or Li+, but the pH1 stayed acidic when Na+-free buffers were used or in the presence of amiloride and its analogues. These results suggest that the pH recovery process after an acid load is due to the Na+/H+ exchange activity in the plasma membrane of the chromaffin cells. The Catecholamine secretion evoked by carbachol and Na+ removal was enhanced after the cytoplasm had been made more acidic. It appears that acidic pH favors the occurrence of exocytosis.