HORMONAL-STIMULATION OF CALCIUM MOBILIZATION IN THE ISOLATED-PERFUSEDRAT PANCREAS

Hormone-stimulated cellular Ca2+ mobilization in the isolated perfused rat pancreas was investigated by analyzing the efflux profiles of Ca- 45(2+) from Ca-45(2+)-loaded pancreata following agonist stimulation. The increased Ca-45(2+) efflux reflects the enhanced exchange of Ca2across the plasma membrane as a result of increased [Ca2+](i). Both hi gh and low concentrations of the cholecystokinin analog, cerulein, app lied to the isolated perfused pancreas gave rise to an increased relea se of Ca-45(2+). The patterns of the increase in Ca-45(2+) release wer e consistently different for high and low concentrations of the agonis t. Cerulein infused at a concentration of 10(-11) M induced a release of a small but significant amount of Ca-45(2+) which could be abolishe d by 8-(N,N-diethylamine)octyl-3,4,5-trimethoxybenzoate (TMB-8), but w as not affected by ethyleneglycol-bis (beta-aminoethyl ether)-N,N,N',N '-tetraacetic acid (EGTA). Cerulein stimulation at 10(-9) M elicited a marked increase in Ca-45(2+) release which was minimized by EGTA, but not by TMB-8. Also, infusion of cerulein stimulated a concentration-d ependent amylase secretion response which displayed the same TMB-8- an d EGTA-sensitivity pattern as the Ca-45(2+) release response. The pres ent study suggests (i) that cellular Ca2+ influx is a prominent featur e of the increased Ca-45(2+) efflux (i.e., increased [Ca2+](i)) induce d by pharmacological concentrations of cerulein while physiological co ncentrations of cerulein cause an increase in [Ca2+](i) which is due p redominantly to a release of internal Ca2+; and (ii) [Ca2+](i) changes are essential for pancreatic enzyme secretion. Although isolated panc reatic acini or cells may lose their sensitivity and physiological res ponses to various agonists during isolation and preparation, the isola ted perfused pancreas is a suitable and very sensitive model in which to study the physiology of Ca2+ mobilization and enzyme secretion. (C) 1996 Academic Press, Inc.