Intracellular free calcium concentrations in isolated pancreatic acini; effects of secretagogues.

Isolated pancreatic acini were loaded with the calcium selective fluorescent indicator, quin-2. Measurements of cellular K+ content and lactic dehydrogenase release indicated that cell viability was not affected by quin-2 loading. The concentration of intracellular free calcium of unstimulated acinar cells was calculated to be 180 +/- 4 nM. When cells suspended in media containing millimolar calcium were exposed to the secretagogues carbachol and cholecystokinin a rapid increase in [Ca2+]i occurred. Both the amplitude and rate of rise of the concentration increase were dose dependent with [Ca2+]i reaching a maximum of 860 +/- 41 nM. The dose-response relationship coincides with the known concentration dependence of the stimulation of amylase release by these agents. In the absence of extracellular calcium, carbachol was still able to elicit a rise in [Ca2+]i. These studies indicate that pancreatic secretagogues induce an increase in [Ca2+]i of acinar cells, both in the presence or absence of extracellular calcium.