Effect of GTP and Ca2+ on inositol 1,4,5-trisphosphate induced Ca2+ release from permeabilized rat exocrine pancreatic acinar cells.
The effects of Ca2+ and GTP on the release of Ca2+ from the inositol 1,4,5-trisphosphate (IP3) sensitive Ca2+ compartment were investigated with digitonin permeabilized rat pancreatic acinar cells. The amount of Ca2+ released due to IP3 directly correlated with the amount of stored Ca2+ and was found to be inversely proportional to the medium free Ca2+ concentration. Ca2+ release induced by 0.18 microM IP3 was half maximally inhibited at 0.5 microM free Ca2+, i.e. at concentrations observed in the cytosol of pancreatic acinar cells. GTP did not cause Ca2+ release on its own, but a single addition of GTP (20 microM) abolished the apparent desensitization of the Ca2+ release which was observed during repeated IP3 applications. This effect of GTP was reversible. GTP gamma S could not replace GTP. Desensitization still occurred when GTP gamma S was added prior to GTP. The reported data indicate that GTP, stored Ca2+ and cytosolic free Ca2+ modulate the IP3 induced Ca2+ release.
Engling
R
R
Abteilung Anatomie und Zellbiologie der Universität Ulm, FRG.
Föhr
K J
KJ
Kemmer
T P
TP
Gratzl
M
M
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002463:Cell Membrane Permeability; D002469:Cell Separation; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000494:pharmacology*; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology*; D008297:Male; D010179:Pancreas / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
D016244:Guanosine 5'-O-(3-Thiotriphosphate); D015544:Inositol 1,4,5-Trisphosphate; D006160:Guanosine Triphosphate; D002118:Calcium