Effect of atropine, ouabain, antimycin A, and A23187 on "trigger Ca2+ pool" in exocrine pancreas.
45Ca2+ fluxes have been analyzed in dispersed acinar cells prepared from rat pancreas. Sudden addition of carbamylcholine (CCh) to 45Ca2+-preloaded acinar cells at quasi-steady state for 45Ca2+ resulted in a quick 45Ca2+ release followed by a slower 45Ca2+ reuptake with net accumulation of 45Ca2+. Subsequent sudden addition of atropine caused a further transient increase in cellular 45Ca2+ followed by a slow decrease to a steady-state value. 45Ca2+ release could not be evoked a second time by pancreozymin when prestimulated with CCh. However, if CCh stimulation was abolished by an interposed step of atropine, restimulation by cholecystokinin-pancreozymin was possible. Addition of A23187 or antimycin A to cells induced a fast decrease in cellular 45Ca2+. This effect was not additive to the CCh effect. In ouabain-pretreated cells, the CCh-induced sudden loss of cellular 45Ca2+ was blocked by 60%. The following slow reuptake of 45Ca2+ was blocked completely. Subsequent addition of atropine caused a fast uptake of cellular 45Ca2+ with no secondary decline. The data are consistent with the following model: acetylcholine releases Ca2+ from a cellular "trigger pool" into the cytosol located in or near the cell membrane. Then Ca2+ is extruded from the cell via Ca2+ pumps partly by a Na+-dependent Ca2+ transport system (quick phase of 45Ca2+ release). Subsequently, due to increased Ca2+ permeability of the plasma membrane as induced by acetylcholine, Ca2+ influx occurs and Ca2+ is taken up from the cytosol into intracellular Ca2+ pools (slow 45Ca2+ reuptake phase). Atropine causes refilling of the trigger Ca2+ pool and return of the increased Ca2+ permeability of the plasma membrane back to the unstimulated state.
D000681:Amylases / Q000378:metabolism; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D000968:Antimycin A / Q000494:pharmacology*; D001285:Atropine / Q000494:pharmacology*; D001693:Biological Transport, Active / Q000187:drug effects; D000001:Calcimycin / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002132:Calcium Radioisotopes; D066298:In Vitro Techniques; D008297:Male; D010042:Ouabain / Q000494:pharmacology*; D010179:Pancreas / Q000378:metabolism*; D051381:Rats
D000900:Anti-Bacterial Agents; D002132:Calcium Radioisotopes; D000001:Calcimycin; D010042:Ouabain; D000968:Antimycin A; D001285:Atropine; D000681:Amylases; D002118:Calcium