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GTP and Ca 2+ Modulate the Inositol 1,4,5‐Trisphosphate‐Dependent Ca 2+ Release in Streptolysin O‐Permeabilized Bovine Adrenal Chromaffin Cells
Author(s) -
Föhr K. J.,
AhnertHilger G.,
Stecher B.,
Scott J.,
Gratzl M.
Publication year - 1991
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1991.tb08201.x
Subject(s) - gtp' , streptolysin , inositol , guanosine , chemistry , biophysics , intracellular , guanosine triphosphate , inositol trisphosphate , calcium , biochemistry , biology , receptor , enzyme , organic chemistry , bacterial protein , gene
The inositol 1,4,5‐trisphosphate (IP 3 )‐induced Ca 2+ release was studied using streptolysin O‐permeabilized bovine adrenal chromaffin cells. The IP 3 ‐induced Ca 2+ release was followed by Ca 2+ reuptake into intracellular compartments. The IP 3 ‐induced Ca 2+ release diminished after sequential applications of the same amount of IP 3 . Addition of 20 μ M GTP fully restored the sensitivity to IP 3 . Guanosine 5′‐ O ‐(3‐thio)triphosphate (GTPγS) could not replace GTP but prevented the action of GTP. The effects of GTP and GTPγS were reversible. Neither GTP nor GTPγS induced release of Ca 2+ in the absence of IP 3 . The amount of Ca 2+ whose release was induced by IP 3 depended on the free Ca 2+ concentration of the medium. At 0.3 μ M free Ca 2+ , a half‐maximal Ca 2+ release was elicited with ∼0.1 μ M IP 3 . At 1 μ M free Ca 2+ , no Ca 2+ release was observed with 0.1 μ M IP 3 ; at this Ca 2+ concentration, higher concentrations of IP 3 (0.25 μ M ) were required to evoke Ca 2+ release. At 8 μ M free Ca 2+ , even 0.25 μ M IP 3 failed to induce release of Ca 2+ from the store. The IP 3 ‐induced Ca 2+ release at constant low (0.2 μ M ) free Ca 2+ concentrations correlated directly with the amount of stored Ca 2+ . Depending on the filling state of the intracellular compartment, 1 mol of IP 3 induced release of between 5 and 30 mol of Ca 2+ .