Catecholamine secretion from digitonin-treated adrenal medullary chromaffin cells

The plasma membrane of cultured chromaffin cells from bovine adrenal medulla was rendered leaky by incubation in low concentrations of digitonin. Digitonin (20 microM) induced Ca2+-dependent release of 10-20% of the catecholamine in the presence of 10 microM Ca2+ without addition of secretagogue. Half-maximal catecholamine release occurred at approximately 1 microM Ca2+ x Mg2+ could not substitute for Ca2+. Cells incubated with digitonin rapidly lost their ability to exclude trypan blue. Digitonin caused release of the cytosolic markers lactic dehydrogenase and phenylethanolamine-N-methyltransferase, but, in contrast to release of catecholamine, the release of the cytosolic proteins was inhibited by Ca2+. Soluble dopamine-beta-hydroxylase, a protein marker of granule contents, was released proportionally with catecholamine in a Ca2+ dependent manner. Catecholamine release was optimal in solutions containing MgATP. Hence, digitonin-treated cells, although they lose soluble cytosolic proteins and presumably low molecular weight cytosolic constituents, maintain the Ca2+-dependent reactions of exocytosis in the presence of MgATP. Digitonin-treated chromaffin cells may be a powerful system in which to study the biochemical mechanisms underlying exocytosis.