Mechanism of Na+ deprivation-induced catecholamine secretion from freshly isolated bovine adrenal chromaffin cells |
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Authors: | Isosaki M Nakashima T |
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Affiliation: | Department of Pharmacology, Nara Medical University, Kashihara, Nara, Japan. misosaki@naramed-u.ac.jp |
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Abstract: | We have studied the mechanism of Na+ deprivation-induced catecholamine secretion from freshly isolated bovine adrenal chromaffin cells. Na+ deprivation-induced catecholamine secretion depended on free extracellular Ca2+ concentrations and was almost parallel to 45Ca2+ influx into the cells under various experimental conditions. Furthermore, Na+ deprivation-induced 45Ca2+ influx and catecholamine secretion were actually induced by a relative Na+ concentration gradient across the plasma membrane, but not by simple omission of Na+ from the medium. These results indicate that the deprivation of Na+ from the medium changes the relative Na+ gradient across the plasma membrane and results in Ca2+ influx via a reverse mode of Na(+)-Ca(2+) exchange rather than by inducing Ca2+ entry through Ca2+ channels by eliminating the competition between extracellular Na+ and Ca2+. |
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