Specific and nonspecific effects of nucleotides on hormone-induced phosphoinositide turnover in permeabilized human pituitary tumour cells (Flow 9000).
Previous studies have shown that agonist-induced inositol phosphate formation in the human embryonic pituitary cell line Flow 9000 is regulated by guanine nucleotides, and it is likely that a guanine nucleotide-binding protein is involved in coupling receptors to phosphoinositidase C (PIC) [(1986) Biochem.Soc.Trans. 14, 1135-1136]. We have now tested the specificity of various nucleotides in regulating PIC activity in the absence or presence of the hormone cholecystokinin (CCK-8) in saponin-permeabilized [3H]inositol-labelled Flow 9000 cells. We found that all nucleotides tested (i.e. CTP, UTP, ITP, TTP, GTP, GppNHp, GTP[S], ATP, AppNHp and ATP[S]) stimulated total [3H]inositol phosphate ([3H]IP) formation in a dose-dependent manner with similar potency and efficacy. However, only guanine nucleotides significantly enhanced CCK-8 stimulation of [3H]IP production. These results indicate a physiological role for guanine nucleotides in regulating hormone-induced phosphoinositide turnover. In addition, the effects of nucleotides on calcium-dependent PIC activity are discussed.
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Parke-Davis Research Unit, Addenbrookes Hospital Site, Cambridge, England.
Hughes
J
J
D002118:Calcium / Q000494:pharmacology; D002460:Cell Line; D002463:Cell Membrane Permeability; D006801:Humans; D007700:Kinetics; D010716:Phosphatidylinositols / Q000096:biosynthesis / Q000378:metabolism*; D010911:Pituitary Neoplasms / Q000378:metabolism*; D012265:Ribonucleotides / Q000494:pharmacology*; D012503:Saponins
D010716:Phosphatidylinositols; D012265:Ribonucleotides; D012503:Saponins; D002118:Calcium