Abstract
The effect of amiloride on ouabain-evoked catecholamine secretion was investigated in primary cultures of bovine adrenal chromaffin cells. Catecholamine secretion evoked by ouabain was inhibited markedly by amiloride, but the secretion evoked by Na+ removal was not affected by the drug. In contrast, adriamycin, a putative inhibitor of the Na(+)-Ca++ exchange, inhibited the secretion evoked by Na+ removal as well as that evoked by ouabain. The inhibitory action of amiloride on the ouabain-evoked secretion was therefore considered to be due to its action on other mechanism(s) than the Na(+)-Ca++ exchange process. Further studies showed that the uptake of 86Rb+ into the cells was slightly but significantly reduced by amiloride, and the inhibitory action of ouabain on 86Rb+ uptake was considerably blocked by this drug under the experimental conditions in which the inhibition of ouabain-evoked secretion was observed. The binding of [3H] ouabain to the intact cells was also inhibited by amiloride under the same conditions. These results suggest that amiloride may inhibit ouabain-evoked catecholamine secretion as a consequence of blocking the inhibitory action of ouabain on the plasma membrane Na+/K(+)-pump in adrenal chromaffin cells.
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