Effect of inositol 1,4,5-trisphosphate and GTP on calcium release from pituitary microsomes |
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| Authors: | L Kiesel G L Lukács I Eberhardt B Runnebaum A Sp?t |
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| Affiliation: | 1. Department of Gynecology and Obstetrics, University of Heidelberg, D-6900 Heidelberg, FRG;2. Department of Physiology, Semmelweis University Medical School, PO Box 259, H-1444 Budapest, Hungary |
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| Abstract: | Microsomal vesicles from bovine anterior pituitary accumulate Ca2+ and maintain a steady-state ambient Ca2+ level of 200 nM. IP3 and GTP both induce calcium release from the microsomal vesicles. The effect of IP3 is inhibited by polyethylene glycol (PEG), and the effect of GTP is absolutely dependent on PEG. Half-maximal effect of IP3 (without PEG) is 0.26 micron, the maximal calcium release attaining 7% of the A23187-releasable pool. The same values for GTP (in the presence of PEG) are 80 microM and 10%, respectively. GTP potentiates the effect of IP3. This potentiation is not mediated by protein phosphorylation. |
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