Reciprocal effects of the protein kinase C inhibitors staurosporine and H-7 on the regulation of glycogen synthase and phosphorylase in the primary culture of hepatocytes.
The effects of the protein kinase C inhibitors staurosporine and H-7 [1-(5-isoquinolinylsulfonyl)-2-methylpiperazine] on glucose-induced regulation of glycogen synthase and phosphorylase activities were investigated in the primary culture of hepatocytes. Glycogen synthesis as measured by the incorporation of [14C]glucose into glycogen was enhanced up to 78% (P < .001) by 100 nmol/L staurosporine. In contrast, H-7 inhibited glycogen synthesis in a dose-dependent manner, with an IC50 value of 70 mumol/L. Activation of glycogen synthase by 30 mmol/L glucose was enhanced significantly (P < .02 and less) by staurosporine at 20 nmol/L and higher concentrations whereas the activity of this enzyme was inhibited by H-7 (IC50 = 50 mumol/L). The inactivation of phosphorylase by glucose was significantly greater when staurosporine was included in the medium. However, H-7 increased the phosphorylase activity ratio by 1.5- to 2.5-fold at concentrations of 20 to 100 mumol/L. The time course of synthase activation and phosphorylase inactivation showed that the effect of glucose was enhanced by staurosporine and inhibited by H-7. These novel reciprocal effects of protein kinase C inhibitors were also observed at different concentrations of glucose. The effects of H-8, a compound with structural resemblance to H-7 and an inhibitor of protein kinase A, were similar to those of staurosporine but not to those of H-7. Staurosporine blocked the effects of vasopressin and 4 beta-phorbol 12 beta-myristate 13 alpha-acetate (PMA), whereas H-7 in combination with these protein kinase C activators acted in the same direction. The effects of staurosporine, a relatively more specific inhibitor of protein kinase C, indicated that this enzyme plays a role in the regulation of glycogen metabolism in liver. However, H-7, which is known to have protein kinase C-independent effects in intact cells, seems to alter the activities of glycogen synthase and phosphorylase by a different mechanism.
Gali
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Department of Biochemistry, University of Saskatchewan, Saskatoon, Canada.
Pugazhenthi
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Khandelwal
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D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D000470:Alkaloids / Q000494:pharmacology*; D000818:Animals; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D005947:Glucose / Q000378:metabolism; D006003:Glycogen / Q000096:biosynthesis; D006006:Glycogen Synthase / Q000096:biosynthesis*; D007546:Isoquinolines / Q000494:pharmacology*; D008099:Liver / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D006005:Phosphorylases / Q000096:biosynthesis*; D010879:Piperazines / Q000494:pharmacology*; D047428:Protein Kinase Inhibitors; D051381:Rats; D017207:Rats, Sprague-Dawley; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013997:Time Factors; D014667:Vasopressins / Q000037:antagonists & inhibitors / Q000494:pharmacology
D000470:Alkaloids; D007546:Isoquinolines; D010879:Piperazines; D047428:Protein Kinase Inhibitors; D014667:Vasopressins; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D006003:Glycogen; D006005:Phosphorylases; D006006:Glycogen Synthase; D019311:Staurosporine; D005947:Glucose; D013755:Tetradecanoylphorbol Acetate