In vitro studies on a cation dependent catecholamine release from a two-compartment storage in bovine adrenal medullary granules

Abstract

Perfusion of isolated adrenal medullary granules, with isotonic cation-containing solutions (NaCl, KCl, LiCL) caused a concentration dependent release of CA [catecholamine]. The course of the release indicated the existence of a 2-compartment storage of CA. The minor compartment (pool 1) with a Umax [maximum uptake] of .apprx. 500 nmol/mg granule dry weight showed the characteristics of a cation exchanger and was assumed to be depleted on exposure to cations, e.g., Na ions, as an ion exchange Na+ .dblarw. CA+. The major compartment (pool 2) with a Umax of .apprx. 1000 nmol/mg stored both CA and ATP. It was assumed to empty via the cation exchanger pool. The total storage capacity of the 2 compartments .apprx. 1500 nmol/mg matched the in vivo storage capacity for CA (.apprx. 1300 nmol/mg).