P2-purinergic control of liver glycogenolysis

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Abstract
Purinergic agonists cause a dose-dependent activation of glycogen phosphorylase in isolated rat hepatocytes. Half-maximally effective concentrations are 5 .times. 10-7 M for ATP, 2 .times. 10-6 M for ADP, and about 5 .times. 10-5 M for AMP and adenosine. This potency series indicates the presence of P2-purinergic receptors. The mode of action of ATP appears to be identical with that of the Ca2+-dependent glycogenolytic hormones angiotensin, vasopressin and .alpha.1-adrenergic agonists. (1) They all require Ca2+ for phosphorylase activation; (2) they do not increase cyclic AMP levels; (3) they are susceptible to heterologous desensitization by vasopressin and phenylephrine; (4) they lower cyclic AMP concentrations in hepatocytes stimulated by glucagon, most probably mediated by an enhanced phosphodiesterase activity.

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