Cookies on this website
We use cookies to ensure that we give you the best experience on our website. If you click 'Continue' we'll assume that you are happy to receive all cookies and you won't see this message again. Click 'Find out more' for information on how to change your cookie settings.

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.

Type

Journal article

Journal

J Membr Biol

Publication Date

07/1989

Volume

109

Pages

173 - 186

Keywords

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