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Abstract

Addition of 0.1 mmol/l of La²⁺ to pancreatic acinar cells increased both the rate and extent of ⁴⁵Ca²⁺ uptake. Addition of 0.3 mmol/l La²⁺ 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 vCa²⁺ 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.