Characterization of inositol 1,4,5-trisphosphate-sensitive (IsCaP) and -insensitive (IisCaP) nonmitochondrial Ca2+ pools in rat pancreatic acinar cells.
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.
Thévenod
F
F
Max-Planck-Institut für Biophysik, Frankfurt am Main, Federal Republic of Germany.
Dehlinger-Kremer
M
M
Kemmer
T P
TP
Christian
A L
AL
Potter
B V
BV
Schulz
I
I
D009327:4-Chloro-7-nitrobenzofurazan / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D017920:Antiporters; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D027682:Cation Transport Proteins; D002463:Cell Membrane Permeability; D004721:Endoplasmic Reticulum / Q000648:ultrastructure; D005033:Ethylmaleimide / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate; D007295:Inositol Phosphates / Q000494:pharmacology*; D007425:Intracellular Membranes / Q000378:metabolism; D008297:Male; D009550:Nigericin / Q000494:pharmacology; D010179:Pancreas / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D051381:Rats; D011919:Rats, Inbred Strains; D013403:Sugar Phosphates / Q000494:pharmacology*; D014638:Vanadates / Q000494:pharmacology
D017920:Antiporters; D002135:Calcium-Binding Proteins; D027682:Cation Transport Proteins; D007295:Inositol Phosphates; D013403:Sugar Phosphates; C027614:calcium-hydrogen antiporters; D014638:Vanadates; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D015544:Inositol 1,4,5-Trisphosphate; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; D009327:4-Chloro-7-nitrobenzofurazan; D005033:Ethylmaleimide; D009550:Nigericin; D002118:Calcium