Effects of hypertonic solutions on catecholamine release from cat adrenal glands

Abstract

The effects of hypertonic solutions on the spontaneous and evoked catecholamine release from isolated, perfused cat adrenal glands were studied. Hypertonic solutions enhanced three times the spontaneous release of the amines, but markedly inhibited the release evoked by nicotine 15μM for 2 min or high K +(17.7 mM for 2 min). Using sucrose as osmoticant, the secretory response to high K + was decreased to 53 and 15% of controls at 344 and 416 mosM, respectively At 512 mosM sucrose inhibited poorly the release of catecholamines evoked by nicotine, but reduced it by 90% at 1000 mosM; sodium chloride behaved similarly to sucrose. A rise in the osmolarity of only 7.5% with choline chloride produed a complete inhibition of the K +-evoked response. These effects were not seen using isotonic choline chloride; on the contrary, isotonic choline chloride enhanced the K + response, probably by stimulating nicotinic receptors. Since atropine did not modify this effect, it seems that secretion of catecholamines evoked by choline is mediated by nicotinic receptors. While the inhibitory effects of sucrose and NaCl were completely reversed when the tonicity of the perfusion medium was restored to its normal value (320 mosM), the effects of choline seemed to be long lasting and were reversed only partially. It is worth noting that the inhibitory effects of hyperosmotic solutions developed very fast. It is concluded that an increase in the tonicity of the medium bathing the chromaffin cell depresses profoundly the exocytotic catecholamine release response to nicotine and high K + these experiments suggest that the existence of an osmotic gradient across the plasma and or vesicular membranes might be a prerequisite for fusion of both membranes and or the subsequent extracellular discharge of chromaffin granule contents to the cell exterior.