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We have measured Ca2+ uptake and Ca2+ release in isolated permeabilized pancreatic acinar cells and in isolated membrane vesicles of endoplasmic reticulum prepared from these cells. Ca2+ uptake into cells was monitored with a Ca2+ electrode, whereas Ca2+ uptake into membrane vesicles was measured with 45Ca2+. Using inhibitors of known action, such as the H+ ATPase inhibitors NBD-Cl and NEM, the Ca2+ ATPase inhibitor vanadate as well as the second messenger inositol 1,4,5-trisphosphate (IP3) and its analog inositol 1,4,5-trisphosphorothioate (IPS3), we could functionally differentiate two nonmitochondrial Ca2+ pools. Ca2+ uptake into the IP3-sensitive Ca2+ pool (IsCaP) occurs by a MgATP-dependent Ca2+ uptake mechanism that exchanges Ca2+ for H+ ions. In the absence of ATP Ca2+ uptake can occur to some extent at the expense of an H+ gradient that is established by a vacuolar-type MgATP-dependent H+ pump present in the same organelle. The other Ca2+ pool takes up Ca2+ by a vanadate-sensitive Ca2+ ATPase and is insensitive to IP3 (IisCaP). The IsCaP is filled at "higher" Ca2+ concentrations (approximately 10(-6) mol/liter) which may occur during stimulation. The low steady-state [Ca2+] of approximately 10(-7) mol/liter is adjusted by the IisCaP. It is speculated that both Ca2+ pools can communicate with each other, the possible mechanism of which, however, is at present unknown.


Journal article


J Membr Biol

Publication Date





173 - 186


4-Chloro-7-nitrobenzofurazan, Adenosine Triphosphate, Animals, Antiporters, Biological Transport, Calcium, Calcium-Binding Proteins, Calcium-Transporting ATPases, Carbonyl Cyanide m-Chlorophenyl Hydrazone, Cation Transport Proteins, Cell Membrane Permeability, Endoplasmic Reticulum, Ethylmaleimide, Inositol 1,4,5-Trisphosphate, Inositol Phosphates, Intracellular Membranes, Male, Nigericin, Pancreas, Rats, Rats, Inbred Strains, Sugar Phosphates, Vanadates