Calcium translocation in the rough endoplasmic reticulum during stimulation of pancreatic enzyme secretion

washed free of EGTA and incubated for 30min at 37°C in Hepes-buffered Ringer solution (see Dormer, 1983). Amylase release was measured after centrifugation and resuspension of acini in fresh medium in the presence or absence of carbamylcholine. The secretory responses of acini swollen in the absence of EGTA were similar to those of unswollen acini. Thus, the dose-response to carbamylcholine was the same, with a maximum rate of amylase release at 3 pwcarbamylcholine. The maximum degree of stimulation was 551% for unswollen acini and 610% for swollen acini. As shown in Table 1, treatment ofunswollen acini with IO~M-EGTA for 30min resulted in a decrease in the subsequent response of isolated acini to a submaximal (0.3 p ~ ) or maximal (3 pM) concentration of carbamylcholine. However, when EGTA was incorporated by swelling, the response to 0.3 p ~ carbamylcholine was totally blocked and that of 3 p ~ carbamylcholine was inhibited by 77%. This effect was not due to ATP depletion since acini swollen in the presence or absence of EGTA had the same ATP content as unswollen acini. Measurement of total Ca2+ content of swollen acini also showed that EGTA did not result in a lowering of total cell Caz+. In conclusion, it has been demonstrated that incorporation of a Ca2+ chelator into isolated pancreatic acini inhibits amylase release in response to carbamylcholine with a greater effect being observed at lower doses of agonist. This effect was not due to ATP or total cell Caz+ depletion. These results provide direct evidence that pancreatic enzyme secretion is dependent upon a rise in the cytosolic free Ca2+.