Role of a guanine nucleotide-binding regulatory protein in the hydrolysis of hepatocyte phosphatidylinositol 4,5-bisphosphate by calcium-mobilizing hormones and the control of cell calcium. Studies utilizing aluminum fluoride.
Treatment of isolated hepatocytes with NaF produced a concentration-dependent activation of phosphorylase, inactivation of glycogen synthase, efflux of Ca2+, rise in cytosolic free Ca2+ ([Ca2+]i), increase in myo-inositol-1,4,5,-P3 levels, decrease in phosphatidylinositol-4,5-P2 levels, and increase in 1,2-diacylglycerol levels. These changes were evident within 1 min and maximum at 2-5 min. Maximum effects on Ca2+ efflux, [Ca2+]i, glycogen synthase, and phosphorylase were observed with 15 mM NaF, whereas myo-inositol-1,4,5-P3 and 1,2-diacylglycerol levels were maximally stimulated by 50 mM NaF. The levels of intracellular cAMP were decreased by NaF (up to 10 mM) in the absence or presence of glucagon (0.1-1 nM) or forskolin (2 microM). The effects of low doses of NaF (2-15 mM) to inhibit basal or glucagon-stimulated cAMP accumulation, mobilize Ca2+, activate phosphorylase, and inactivate glycogen synthase were all potentiated by AlCl3. This potentiation was abolished by the Al3+ chelator deferoxamine. These results illustrate that AlF4- can mimic the effects of Ca2+-mobilizing hormones in hepatocytes and suggest that the coupling of the receptors for these hormones to the hydrolysis of phosphatidylinositol-4,5-P2 to myo-inositol 1,4,5-P3 is through a guanine nucleotide-binding regulatory protein. This is because AlF4- is known to modulate the activity of other guanine nucleotide regulatory proteins (Ni, Ns, and transducin).
D000535:Aluminum / Q000494:pharmacology*; D017607:Aluminum Compounds; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D004789:Enzyme Activation; D005459:Fluorides; D019204:GTP-Binding Proteins / Q000378:metabolism*; D005934:Glucagon / Q000494:pharmacology; D006006:Glycogen Synthase / Q000378:metabolism; D006868:Hydrolysis; D066298:In Vitro Techniques; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D019269:Phosphatidylinositol 4,5-Diphosphate; D010716:Phosphatidylinositols / Q000378:metabolism*; D010762:Phosphorylase a / Q000378:metabolism; D051381:Rats; D012969:Sodium Fluoride / Q000494:pharmacology; D014667:Vasopressins / Q000494:pharmacology*
D017607:Aluminum Compounds; D019269:Phosphatidylinositol 4,5-Diphosphate; D010716:Phosphatidylinositols; D014667:Vasopressins; D005576:Colforsin; D012969:Sodium Fluoride; D005934:Glucagon; D000535:Aluminum; D000242:Cyclic AMP; D010762:Phosphorylase a; D006006:Glycogen Synthase; D019204:GTP-Binding Proteins; D005459:Fluorides; D002118:Calcium; C032311:aluminum fluoride