Possible role of nerve impulse induced sodium ion flux in a proposed multivesicular fractional release of adrenaline and noradrenaline from the chromaffin cell

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Abstract
Based on observations concerning a 2-compartment storage of CA [catecholamine] in the adrenal medulla and a cation exchange dependent release of CA from perfused bovine chromaffin granules in vitro, together with reports from other laboratories about the importance of Na ions for CA release from the adrenal gland, a modification of the current quantal theory of CA secretion is proposed. Instead of secretion of quanta, each quantum corresponding to the content of 1 vesicle, a concomitant fractional release of CA from multiple vesicles adjacent to the chromaffin cell membrane is envisaged. The CA secretion should be the result of a cation exchange across the contact area between the plasma membrane and the granule membrane during the period of depolarization caused by the nerve impulse. The size of the released quanta should be determined by the nerve impulse induced Na ion flux and the number of such ions which reach the CA binding ionic sites in the cation exchanger pool (the release pool) of the granules.

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