Induction of Enzyme Secretion in Rat Pancreatic Slices Using the Ionophore A-23187 and Calcium

SUMMARY The divalent cation ionophore A-23187 increased the rate of enzyme secretion in the rat pancreas. As in the secretion induced through the cholinergic receptor, the ionophore causes a specific secretion of digestive enzymes which re- quires calcium in the medium and is dependent on efficient ATP production by oxidative phosphorylation. It is sug- gested that the activation of the cholinergic receptor intro- duces calcium into the cell to act as a second messenger in the process of enzyme secretion. Secretion of digestive enzymes from exocrine glands was ex- tensively studied in the pancreas (I-3) and parotid gland (4, 5). These studies revealed that enzyme secretion operates via two major pathways: the one in the pancreas, which is Ca”+-de- pendent and involves cholinergic and peptide hormone receptors (6, 7), and the second in the parotid, which does not depend on the presence of Ca2+ in the medium and operates via a P-adre- nergic receptor and adenosine 3’: 5’.monophosphate (5). We have recently found that in the parot)id, epinephrine, which causes enzyme secretion through a fi-adrenergic receptor, also acts on an ol-adrenergic receptor causing a Ca2+-dependent K+ release (8). Using a rat parotid slice system, we also showed that calcium, acting through the divalent cation ionophore A-23187, mimics the cy-adrenergic response while having. little effect on enzyme secretion (9). The ionophore A-23187, first described by Reed and Lardy (lo), has been found useful in probing the effect of CaZf m various tissues (11). In the presence of Ca2+ it causes K+ release from rat erythrocytes