Stimulation of glycogenolysis by beta adrenergic agonists in skeletal muscle of mice with the phosphorylase kinase deficiency mutation (i strain)

Gross, S.R.; Mayer, S.E.; Longshore, M.A.

Journal of Pharmacology and Experimental Therapeutics 198(3): 526-538


ISSN/ISBN: 0022-3565
PMID: 978457
Accession: 006481753

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The mechanism by which beta adrenergic agonist stimulate glycogenolysis in intact skeletal muscle was investigated in mice with the phosphorylase kinase deficiency mutation (I strain). Although extracts of I strain diaphragm muscle had only 3.7% of the phosphorylase kinase activity found in extracts of the control strain (C57BL), incubation of I strain hemidiaphragms in Krebs-Ringer bicarbonate buffer with either isoproterenol or epinephrine resulted in a stimulation of the rate of glycogenolysis. In C57BL diaphragms, the EC50 values for isoproterenol and epinephrine were 2 and 14 nM, respectively. With I strain diaphragms, dl-isoproterenol or l-epinephrine stimulated glycogenolysis as a linear function of the log of the drug concentration with no apparent plateau of response up to concentrations of 30 to 40 mugM. For each 10-fold increase in drug concentration, isoproterenol and epinephrine stimulated glycogenolysis in I strain muscles an additional 0.37 to 0.42 mg/g/hr, a slope in the concentration-response relationship of 0.17 and 0.37, respectively, of that measured in C57BL diaphragms at concentrations around the EC50. The highest glycogenolytic response measured in I strain hemidiaphragms (at 40 mugM isoproterenol) was 80% of the maximal catecholamine-stimulated glycogenolysis in C57BL diaphragms. Both 4 nM and 4 mugM isoproterenol, in a concentration-dependent manner, stimulated phosphorylase b to a conversion in I and C57BL diaphragms and increased cyclic adenosine 3':5'-monophosphate (cyclic AMP) concentrations. The glycogenolytic response to 10.1 nM dl-isoproterenol in both I and C57BL diaphragms was blocked by 34 nM l-propranolol but not by 34 nM d-propranolol. The response to 4 mugM isoproterenol was enhanced by the cyclic nucleotide phosphodiesterase inhibitors papaverine (27 mugM) or dl-4-(3-butoxy-4-methoxybenzyl)-2-imidazolidinone (Ro 20-1724, 3 mugM). From the results of these studies, we conclude: 1) Catecholamines stimulate glycogenolysis in skeletal muscle of I mice, as in C57BL mice, by interacting with the beta adrenergic receptor, thereby increasing tissue cyclic AMP concentrations and stimulating phosphorylase b to a conversion. 2) alternative hypotheses for the mechanism of the catecholamine-stimulated decrease in glycogen concentration in I skeletal muscle-inhibition of glycogen synthesis, hyposia and 5'-AMP stimulation of phosphorylase b activity-have been ruled out. 3) the activity of the mutant phosphorylase kinase, although it is only 3.7% of that in extracts of C57BL muscle, is sufficient to produce phosphorylase b to a conversion and thereby account for the glycogenolytic response of I strain muscle to catecholamines.