Proportional secretion of opioid peptides and catecholamines from adrenal chromaffin cells in culture

Abstract

Bovine adrenal medullary chromaffin cells were used to study the relationship between opioid peptide and catecholamine secretion from the adrenal medulla. Stimulation of chromaffin cells by acetylcholine, nicotine, veratridine, barium, or Ionomycin produced secretion of opioid peptides and catecholamines which was proportional to the cellular content of these substances. Nicotine-evoked secretion of opioid peptides and catecholamines was dependent on extracellular calcium and was blocked by d-tubocurarine. Increased cellular content of opioid peptides and decreased catecholamine content induced by treatment of chromaffin cells with reserpine or tetrabenazine were reflected in the secretion of proportionally larger amounts of opioid peptides and smaller amounts of catecholamines when compared with secretion of these substances from untreated cells. Peptides of up to 25,000 daltons that express opiate activity only following digestion with enzymes, such s trypsin and carboxypeptidase B, also are secreted from chromaffin cells in the same proportion of their cellular content as are catecholamines and opioid peptides. Opioid peptides were secreted in proportion to total catecholamines but not in proportion to either epinephrine or norepinephrine alone, suggesting that the peptides are secreted from both epinephrine- and norepinephrine-containing cells in the cultures. The results are consistent with the co-storage of opioid peptides and opiate receptor-inactive peptides containing enkephalin sequences in chromaffin vesicles and with the all-or-none exocytotic secretion of chromaffin vesicles content in response to stimulation of the adrenal medulla.