The route of Ca2+ entry during reloading of the intracellular Ca2+ pool in pancreatic acini.
To trace the route of Ca2+ entry and the role of the cytosolic Ca2+ pool in reloading of the internal stores of pancreatic acinar cells, Mn2+ influx into Fura 2-loaded cells and the effect of 1,2-bis(2-aminophenoxyethane-N,N,N',N'-tetraacetic acid (BAPTA) on Ca2+ storage in intracellular stores and reloading were examined. Treatment of acini suspended in Ca2(+)-free medium with carbachol (cell stimulation) or carbachol and atropine (reloading period) resulted in 2-fold increase in the rate of Mn2+ influx. Increasing Ca2+ permeability of the plasma membrane by elevation of extracellular pH from 7.4 to 8.2 further increased the rate of Mn2+ influx observed during cell stimulation and the reloading period. Loading the acini with BAPTA by incubation with 50 microM of the acetomethoxy form of BAPTA (BAPTA/AM) was followed by a transient reduction in free cytosolic Ca2+ concentration ((Ca2+]i). To compensate for the increased Ca2+ buffering capacity in the cytosol the acini incorporated Ca2+ from the external medium. Although BAPTA prevented changes in free cytosolic Ca2+ concentration during carbachol and atropine treatment, it had no apparent effect on Ca2+ content of the internal stores or the ability of agonists to release Ca2+ from these stores. Loading the cytosol with BAPTA considerably reduced the rate of Ca2+ reloading. These observations are not compatible with direct communication between the medium and the inositol 1,4,5-trisphosphate releasable pool and provide direct evidence for Ca2+ entry into the cytosol prior to its uptake into the intracellular pool, both during cell stimulation and the Ca2+ reloading.
Muallem
S
S
Department of Physiology, University of Texas Southwestern Medical Center, Dallas 75235.
Khademazad
M
M
Sachs
G
G
D000818:Animals; D001285:Atropine / Q000494:pharmacology; D001572:Benzofurans; D002118:Calcium / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D002712:Chlorides; D003600:Cytosol / Q000378:metabolism; D004072:Digitonin / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology / Q000031:analogs & derivatives; D005456:Fluorescent Dyes; D016257:Fura-2; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007700:Kinetics; D008345:Manganese / Q000378:metabolism / Q000494:pharmacology; D017895:Manganese Compounds; D010179:Pancreas / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D012844:Sincalide / Q000494:pharmacology
D001572:Benzofurans; D002712:Chlorides; D005456:Fluorescent Dyes; D017895:Manganese Compounds; D008345:Manganese; D004533:Egtazic Acid; D001285:Atropine; D002217:Carbachol; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D004072:Digitonin; D012844:Sincalide; C025340:manganese chloride; D002118:Calcium; D016257:Fura-2