ION MOVEMENTS IN ISOLATED BOVINE ADRENAL-MEDULLARY CELLS TREATED WITH OUABAIN

  • 1 January 1983
    • journal article
    • research article
    • Vol. 23  (3) , 681-697
Abstract
Ouabain enhances the exocytotic release of catecholamines from isolated bovine adrenal medullary cells. This effect is dependent upon extracellular Na, but persists in the nominal absence of Ca. In this paper the study has been extended to include an investigation of the effects of ouabain on the fluxes of 86Rb, 42K, 24Na and 45Ca in these cells. The basic features of the chromaffin cell Na pump are characterized; both the pump itself (i.e., the kinetics and properties of transport) and its inhibition by ouabain resemble those of squid axons and erythrocytes. Serious doubts are cast upon the often-stated possibility that there is a direct link between Na pump inhibition and exocytotic secretion because parallel measurements of both phenomena have, for example, shown that while the secretory effect of ouabain is Na-dependent, pump inhibition is not. Instead, an entirely different explanation is suggested by the discovery that ouabain produces a marked decrease in the rate of active Ca extrusion from chromaffin cells, under all conditions in which catecholamine secretion is enhanced. This inhibition seems not to be accompanied by any change in Ca influx, and may therefore provide a direct explanation for the rise in free Ca which is required to stimulate exocytosis in this tissue.

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