H+ uptake increases GTP-induced connection of inositol 1,4,5-trisphosphate- and caffeine-sensitive calcium pools in pancreatic microsomal vesicles.
Evidence suggests that GTP but not GTP gamma S activates Ca2+ movement between myo-inositol 1,4,5-trisphosphate (IP3)-sensitive and -insensitive Ca2+ pools (1). Measuring 45Ca2+ uptake into pancreatic microsomal vesicles we have determined the sizes of three different Ca2+ pools which release Ca2+ in response 1) to IP3, 2) to caffeine, and 3) to both IP3 and caffeine ("common" Ca2+ pool). In the presence of GTP the size of the IP3-sensitive Ca2+ pool is decreased whereas the "common" Ca2+ pool is increased as compared to control Ca2+ pool sizes in the presence of GTP gamma S. This effect of GTP is inhibited by bafilomycin B1, a specific inhibitor of vacuolar type H+ ATPases (2). We conclude that GTP induced connection between IP3- and caffeine-sensitive Ca2+ pools is triggered by intravesicular acidification and involves function of small GTP-binding proteins, known to mediate interorganelle transfer.
Ozawa
T
T
Max-Planck-Institut für Biophysik, Frankfurt am Main, Fed. Rep. of Germany.
Schulz
I
I
D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000494:pharmacology*; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology*; D007425:Intracellular Membranes / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D018942:Macrolides; D008861:Microsomes / Q000187:drug effects / Q000378:metabolism*; D008954:Models, Biological; D010070:Oxalates / Q000494:pharmacology; D010179:Pancreas / Q000378:metabolism*; D011092:Polyethylene Glycols / Q000494:pharmacology; D006180:Proton-Translocating ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism*
D000900:Anti-Bacterial Agents; D018942:Macrolides; D010070:Oxalates; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D002110:Caffeine; D011092:Polyethylene Glycols; D015544:Inositol 1,4,5-Trisphosphate; D006160:Guanosine Triphosphate; C052501:bafilomycin B1; D006180:Proton-Translocating ATPases; D002118:Calcium