Agonist-sensitive calcium pool in the pancreatic acinar cell. II. Characterization of reloading.
45Ca2+ fluxes and free cytosolic Ca2+ measurements in guinea pig pancreatic acini indicated that after agonist stimulation and the release of Ca2+ from the agonist-sensitive pool at least part of the Ca2+ is extruded from the cell, resulting in 45Ca2+ efflux. In the continued presence of agonist, the pool remains permeable to Ca2+ but partially refills with Ca2+. This reloading is dependent on the concentration of extracellular Ca2+. In the absence of extracellular Ca2+, the pool is completely depleted of Ca2+. However, with increasing concentrations of CaCl2 in the incubation solution (from 0.5 to 2.0 mM) there is increasing repletion of the pool with Ca2+ during agonist stimulation. With termination of agonist stimulation, the Ca2+ permeability of the agonist-sensitive pool is rapidly reduced to that measured in the unstimulated cell. As a result, the Ca2+ incorporated into the pool during the stimulation period is rapidly trapped within the pool and exchanges poorly with medium Ca2+. Subsequently, the pool completely refills with Ca2+. The rate of Ca2+ reloading at the termination of agonist stimulation is slower than the conversion of the pool to the impermeable state. In incubation media containing 1.3 mM CaCl2, the half-time for reloading at the termination of stimulation is 5 min. These observations demonstrate the characteristics of Ca2+ reloading of the agonist-sensitive pool both during stimulation and at the termination of stimulation.
D000818:Animals; D001285:Atropine / Q000494:pharmacology; D001572:Benzofurans; D002118:Calcium / Q000378:metabolism*; D002132:Calcium Radioisotopes; D002217:Carbachol / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004533:Egtazic Acid / Q000494:pharmacology; D004987:Ethers / Q000494:pharmacology; D016257:Fura-2; D006168:Guinea Pigs; D066298:In Vitro Techniques; D015759:Ionomycin; D007700:Kinetics; D008954:Models, Biological; D010179:Pancreas / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D012844:Sincalide / Q000494:pharmacology
D001572:Benzofurans; D002132:Calcium Radioisotopes; D004987:Ethers; D004533:Egtazic Acid; D015759:Ionomycin; D001285:Atropine; D002217:Carbachol; D012844:Sincalide; D002118:Calcium; D016257:Fura-2