Ca2+ Uptake Coupled to Glycogen Phosphorolysis in the Glycogenolytic-Sarcoplasmic Reticulum Complex from Rat Skeletal Muscle

Abstract

The glycogenolytic-sarcoplasmic reticulum complex from rat skeletal muscle accumulates Ca2+ upon stimulation of glycogen phosphorolysis in the absence of added ATR It is shown that an efficient Ca2+ uptake involves the sequential action of glycogen phosphorylase, phos-phoglucomutase and hexokinase, which generate low concentrations of ATP (approximately 1-2 μm) compartmentalized in the immediate vicinity of the sarcoplasmic reticulum Ca2+, Mg2+-ATPase (the Ca2+ pump). The Ca2+ uptake supported by glycogenolysis in this subcellular structure is strongly stimulated by micromolar concentrations of AMP. showing that the glycogen phosphorylase associated with this complex is in the dephosphorylated b form. The results point out that the flux through this compartmentalized metabolic pathway should be enhanced in physiological conditions leading to increased AMP concentrations in the sarcoplasm. such as long-lasting contractions and in ischemic muscle. © 1996, Verlag der Zeitschrift für Naturforschung. All rights reserved.