Transmural gradient of glycogen metabolism in the normal rat left ventricle.

The changes of glycogen metabolism with the location of tissue within the ventricle wall have been explored in the rat myocardium. The hearts were cut in 100 microns thick serial sections and all sections were analyzed for their content in glycogen, glucose-6-phosphate, UDPG and glycogen enzymes and for glucose incorporation into glycogen and for the 2-deoxyglucose uptake after the intravenous injection of the 14C-labelled sugars. The rate of glycogen turnover was significantly higher in the subendocardial myocardium (P less than 0.01) and the levels of glucose-6-phosphate and the total (i.e. a + b) activity of glycogen phosphorylase were significantly higher in the subepicardial tissue (P less than 0.01 in both instances). No significant transmural gradient of UDPG was found and transmural changes of total (i.e. I + D) synthase activity were barely significant. These changes in glycogen metabolism may be related to regional differences in the cardiac work load and to a differentiation of the subendocardial and subepicardial heart fibers

The accumulation of 2-deoxyglucose-6-phosphate activates glycogen synthase (and inactivates glycogen phosphorylase) in rat skeletal muscle

In the muscle loaded with 2-dGlc "in vitro" (this sugar is accumulated as hexosephosphate) glycogen synthase I levels are changed by a mechanism which is additive to those of hormones such as insulinor epinephrine. The levels of glycogen phosphorylase are decreased only at the highest 2-dGlc-6-P concentration. The role of this effect of sugar phosphate - which has been attributed to the activation of muscle phosphatase (6) - is discussed with regard to glycogen metabolism during muscle function