ISSN:
1471-4159
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Medicine
Notes:
Abstract: Using mouse brain cortical slices, we investigated the relative roles of cyclic AMP and of calcium ions as the intracellular messengers for the activation of glycogen phosphorylase (EC 2.4.1.1; α-1,4-glucan:orthophosphate glucosyltransferase) induced by noradrenaline and by depolarization. Activation of phosphorylase by 100 μM noradrenaline is mediated by β-adrenergic receptors and does not require the copresence of adenosine. The role of the concomitant small increase in cyclic AMP is questioned. Short-term treatment with EGTA or LaCl3 abolishes the noradrenaline activation of phosphorylase, pointing to a critical role of extracellular calcium. Depolarization by 25 mM K+ or 100 μM veratridine produces a rapid and large (fourfold) activation of phosphorylase. Only veratridine increases the cyclic AMP levels; exogenous adenosine deaminase essentially blocks this cyclic AMP accumulation but not the phosphorylase activation. A halfmaximal activation of phosphorylase occurs at about 12 mM K+. Addition of EGTA or LaCl3, reduces the effect of both depolarizations to a slight and transient activation of phosphorylase. These results indicate that activation of glycogen phosphorylase by K+ or veratridine occurs by a cyclic AMP-independent and calcium-dependent mechanism. The calcium dependency of brain phosphorylase kinase renders this kinase the prime target enzyme for regulation of glycogenolysis by calcium ions.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1471-4159.1982.tb07903.x
Permalink
