Effect of La3+ on secretagogue-induced Ca2+ fluxes in rat isolated pancreatic acinar cells.

Addition of 0.1 mmol/l of La3+ to pancreatic acinar cells increased both the rate and extent of 45Ca+ uptake. Addition of 0.3 mmol/l La3+ did not change cellular 45Ca2+, whereas 1, 2, and 5 mmol/l gradually decreased it. If carbamylcholine (CCh) or the octapeptide of cholecystokinin-pancreozymin (CCK-OP) was added in the presence of low La3+ concentrations (0.1 and 0.3 mmol/l) to 45Ca2+-equilibrated cells, secretagogue-induced 45Ca2+ release-reuptake was not inhibited. At 1 and 2 mol/l of La3+, however, secretagogue-induced 45Ca2+ release was abolished, whereas uptake of 45Ca2+ was still increased by CCK-OP and CCh. At 5 mmol/l La3+, the effects of secretagogues were completely abolished. In the presence of 2 mmol/l La3+, the atropine-induced 45Ca2+ uptake in CCh-pretreated cells and the dibutyryl guanosine 3',5'-cyclic monophosphate-induced 45Ca2+ uptake in CCK-OP-pretreated cells were highly reduced. The data are interpreted to support our assumption that CCK-OP and CCh increase the plasma membrane permeability to Ca2+ in pancreatic acinar cells in addition to their action to initiate release of CA2+ from an intracellular Ca2+ trigger pool.