STIMULUS-SECRETION COUPLING IN ISOLATED BOVINE ADRENAL MEDULLARY CELLS

¹ Department of Physiology, King's College, London WC2R 2LS

Adrenal medullary cells can be obtained in high yield by protease digestion of slices of bovine adrenal medulla. The properties of catecholamine release from these isolated cells have been determined and compared with the intact perfused gland. Exposure to carbamylcholine, veratridine or high K evokes a transient increase in the rate of catecholamine release in association with dopamine hydroxylase but not lactate dehydrogenase. Exposure to A23187 releases catecholamine together with lactate dehydrogenase. In all cases release requires extracellular Ca. A comparison is made of the sensitivities of catecholamine release evoked by various agonists and the effects of nicotinic antagonists, D 600, Na-free media, TTX, Mg and trifluoperazine. Resting and carbamylcholine-evoked catecholamine release is relatively insensitive to the nature of the major extracellular anion and to the external pH over the range 6·4 to 7·8. Measurements with the dye 3 3'-Diethylthiadicarbocyanine iodide (di S-C₂-(5)) show that release evoked by carbamylcholine or low concentrations of veratridine is associated-on average-with a small steady depolarization of the cells. Catecholamine release in response to nicotinic agonists, but not the other secretagogues, is greater at 20 °C than at 37 °C, possibly because of a slower rate of receptor desensitization at this temperature. Transmission electron microscopy of stimulated cells reveals a marked increase in the proportion of large membrane bounded vesicles that lack electron-dense cores. After stimulating secretion in the presence of horseradish peroxidase, the vesicles contain reaction product suggesting that they are generated by endocytosis.

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