EFFECTS OF CYTOPLASMIC AND MICROSOMAL FRACTIONS ON ATP-Mg++ STIMULATED CATECHOLAMINE RELEASE FROM ISOLATED ADRENOMEDULLARY GRANULES

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There is evidence that Ca++ is required for the release of catecholamine from the adrenal medulla evoked by acetylcholine or a high K+ concentration (1, 2) and that an increased influx of Ca++ into the cell occurs during this process (3). It has therefore been proposed that it is the entry of Ca++ into the cell which somehow triggers the secretory process (4, 5). On the other hand, the release of catecholamine from isolated catecholamine storage granules is shown to be stimulated by ATP and Mg++ (6-8) and this ATP-Mg++ stimulated release of catecholamine also requires a low concentration of Ca++ (<10-5M), present as a contaminant in the reaction mixture (9). The authors suggested that ATP-Mg++ stimulated release of catecholamine from the granules could be a step in the secretory response of the adrenal medulla. To elucidate the exact intracellular mechanism of adrenal medullary secretion, it is necessary to determine whether or not intracellular elements other than catecholamine storage granules are involved in the regulation of catecholamine release from the granules. We have investigated the effects of the cytoplasmic and microsomal fractions on ATP-Mg++ stimulated catecholamine release from the granules. Results suggest that these two fractions are important in regulation of catecholamine release from the adrenal medulla.
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