GTP and Ca2+ modulate the inositol 1,4,5-trisphosphate-dependent Ca2+ release in streptolysin O-permeabilized bovine adrenal chromaffin cells.
The inositol 1,4,5-trisphosphate (IP3)-induced Ca2+ release was studied using streptolysin O-permeabilized bovine adrenal chromaffin cells. The IP3-induced Ca2+ release was followed by Ca2+ reuptake into intracellular compartments. The IP3-induced Ca2+ release diminished after sequential applications of the same amount of IP3. Addition of 20 microM GTP fully restored the sensitivity to IP3. Guanosine 5'-O-(3-thio)triphosphate (GTP gamma S) could not replace GTP but prevented the action of GTP. The effects of GTP and GTP gamma S were reversible. Neither GTP nor GTP gamma S induced release of Ca2+ in the absence of IP3. The amount of Ca2+ whose release was induced by IP3 depended on the free Ca2+ concentration of the medium. At 0.3 microM free Ca2+, a half-maximal Ca2+ no Ca2+ release was observed with 0.1 microM IP3; at this Ca2+ concentration, higher concentrations of IP3 (0.25 microM) were required to evoke Ca2+ release. At 8 microM free Ca2+, even 0.25 microM IP3 failed to induce release of Ca2+ from the store. The IP3-induced Ca2+ release at constant low (0.2 microM) free Ca2+ concentrations correlated directly with the amount of stored Ca2+. depending on the filling state of the intracellular compartment, 1 mol of IP3 induced release of between 5 and 30 mol of Ca2+.
Föhr
K J
KJ
Abteilung Anatomie und Zellbiologie der Universität Ulm, F.R.G.
Ahnert-Hilger
G
G
Stecher
B
B
Scott
J
J
Gratzl
M
M
D000311:Adrenal Glands / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D001426:Bacterial Proteins; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology*; D002417:Cattle; D002463:Cell Membrane Permeability / Q000187:drug effects; D002838:Chromaffin System / Q000187:drug effects / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000494:pharmacology*; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology*; D013301:Streptolysins / Q000494:pharmacology
D001426:Bacterial Proteins; D013301:Streptolysins; C025964:streptolysin O; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D015544:Inositol 1,4,5-Trisphosphate; D006160:Guanosine Triphosphate; D002118:Calcium