Ca2+-dependent activation of oxoglutarate dehydrogenase by vasopressin in isolated hepatocytes.
Vasopressin stimulated gluconeogenesis from proline in hepatocytes from starved rats; this was attributed to an activation of oxoglutarate dehydrogenase (EC 1.2.4.2) [Staddon & McGivan (1984) Biochem. J. 217, 477-483]. The role of Ca2+ in the activation mechanism was investigated. (1) In the absence of extracellular Ca2+, vasopressin caused a stimulation of gluconeogenesis and a decrease in cell oxoglutarate content that were markedly transient when compared with the effects in the presence of Ca2+. (2) Ca2+ added to cells stimulated for 2 min by vasopressin in the absence of extracellular Ca2+ sustained the initial effects of vasopressin. Ca2+ added 15 min after vasopressin, a time at which both the rate of gluconeogenesis and the cell oxoglutarate content were close to the control values, caused a stimulation of gluconeogenesis and a decrease in cell oxoglutarate content. (3) Under conditions of cell-Ca2+ depletion, vasopressin had no effect on gluconeogenesis or cell oxoglutarate content. (4) Ionophore A23187 stimulated gluconeogenesis and caused a decrease in cell oxoglutarate content, but the phorbol ester 4 beta-phorbol 12-myristate 13-acetate had no effects. (5) These data suggest that the initial activation of oxoglutarate dehydrogenase by vasopressin is dependent on an intracellular Ca2+ pool and independent of extracellular Ca2+. For activation of a greater duration, a requirement for extracellular Ca2+ occurs. The activation of oxoglutarate dehydrogenase by A23187 is consistent with a mechanism involving Ca2+, but the lack of effect of 4 beta-phorbol 12-myristate 13-acetate indicates that protein kinase C is not involved in the mechanism of activation by vasopressin.
D000818:Animals; D001127:Arginine Vasopressin / Q000494:pharmacology*; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects; D005943:Gluconeogenesis / Q000187:drug effects; D066298:In Vitro Techniques; D007655:Ketoglutarate Dehydrogenase Complex / Q000378:metabolism*; D007658:Ketone Oxidoreductases / Q000378:metabolism*; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D001127:Arginine Vasopressin; D000001:Calcimycin; D007658:Ketone Oxidoreductases; D007655:Ketoglutarate Dehydrogenase Complex; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium