Glucose stimulation of heart phosphorylase phosphatase activity in vitro and in vivo |
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Authors: | Frank Q PJuttall MD PhD Mary C Gannon |
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Institution: | (1) Department of Medicine and the Section of Endocrinology and Metabolism, Minneapolis VA Medical Center and the University of Minnesota, 55417 MN, USA;(2) Chief, Metabolic-Endocrine Section (IIIG), Minneapolis VA Medical Center, 55417 Minneapolis, MI, USA |
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Abstract: | Summary To determine the mechanism of the glucose stimulation, glucose or glucose-6-phospate was added to dilute heart extracts in the presence or absence of AMP. The intracellular glucose, tissue glucose-6-phosphate, and tissue AMP concentrations were also determined in 24-h starved animals given glucose; 24-h starved animals given insulin as well as diabetic starved and diabetic starved insulin-treated animals were also studied.The A0.5 for glucose stimulation of cardiac phosphorylase phosphatase activity was approximately 1 .2 mM. The A0.5 for glucose-6-phosphate was approximately 0.02 mM. The glucose-6-phosphate concentration in all animals exceeded the Ao.5 by 10-fold. However, the intracellular glucose concentration in the glucose-treated, insulin-treated, diabetic, and diabetic insulin-treated rats was in the range of the A0.5 for stimulation of phosphorylase phosphatase activity. AMP completely inhibited phosphorylase phosphatase activity at a concentration of 0.2 mM. Physiological concentrations of glucose and glucose-6-phosphate partially reversed this inhibition. Administration of glucose or insulin resulted in an increase in intracellular glucose concentration, an increase in tissue glucose-6-phosphate and a decrease in tissue AMP concentrations. These data suggest that glucose may be a physiological regulator of phosphorylase phosphatase in heart muscle as it is in liver.Recipient ofaMedical InvestigatorshipAward from theVeterans Administration. |
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Keywords: | adenosine monophosphate glucose glucose-6-phospate intracellular glucose phosphorylase phosphatase |
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