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Regulation of hepatic glycogenolysis by glucagon in male and female rats. Role of cAMP and Ca2+ and interactions between epinephrine and glucagon.

1984; Elsevier BV; Volume: 259; Issue: 6 Linguagem: Inglês

10.1016/s0021-9258(17)43135-8

1083-351X

R. Studer, K. W. Snowdowne, A. B. Borle,

Glycogen Storage Diseases and Myoclonus

The effects of 10"O to lo-? M glucagon on CAMP, phosphorylase a, cell calcium, and glucose production, and glucagon interactions with epinephrine were studied in isolated hepatocytes from adult male and female rats.At physiological concentrations ( 10"10-10-9 M), glucagon activated phosphorylase by increasing cAMP and not by raising the cytosolic free calcium.At supraphysiologic concentrations (and in the male only), glucagon slightly increased the cytosolic free calcium, the fractional efflux of calcium, and, after 2 h, decreased the cell calcium content.Exposure of hepatocytes to the simultaneous administration of lo-' M glucagon and lo-? M epinephrine resulted in a prolongation of the activation of phosphorylase a and a greater release of glucose from glycogen stores than exposure to either agonist alone.In the male, the effects of low concentrations of the two hormones on phosphorylase a activity were additive.Cytosolic free calcium was increased by M epinephrine from 280 to 500 nM while physiological concentrations of glucagon did not change it.In these intact cells, there was no evidence of an a2- adrenergic inhibition of adenyl cyclase and no indication that cAMP depresses the rise in cell calcium induced by a-adrenergic stimuli.