Glycogen metabolism Calcium

H, receptors in brain slices can also stimulate glycogen metabolism [5] and can positively modulate receptor-linked stimulation of cAMP synthesis. The activation of brain cAMP synthesis by histamine is a well studied phenomenon that reveals a positive interaction between histamine receptors [35]. When studied in cell-free preparations, this response shows characteristics of H2, but not H receptors. When similar experiments are performed in brain slices, however, both receptors appear to participate in the response. Subsequent work showed that H receptors do not directly stimulate adenylyl cyclase but enhance the H2 stimulation, probably through the effects of calcium and PKC activation on sensitive adenylyl cyclase iso forms (see Ch. 21). 

Possible mechanism for regulation of glycogen metabolism in skeletal muscle by changes in cytosolic calcium. Increased glycogen breakdown may be coordinated with muscle contractions, as indicated here. The actual control scheme is probably more complicated, since phosphoprotein phosphatases are also involved. Interactions with cAMP-activated reactions, which also may complicate regulation, are not included. 

When bound to calcium, calmodulin plays a special role as an integral subunit of the glycogen metabolism enzyme, phosphorylase b kinase. Hence, the glycogenolysis cascade depends on intracellular calcium concentration as well as on cyclic AMP levels. This dependence is particularly... 

Kuhla, B., D. Albrecht, S. Kuhla and C.C. Metges, 2009. Proteome analysis of fatty liver in feed deprived dairy cows reveals interaction of fuel sensing, calcium, fatty acid and glycogen metabolism. Physiol Genomics 37, 88-98. Eymann, C., D. Becher, J. Bernhardt, K. Gronau, A Klutzny and M. flecker, 2007. Dynamics of protein phosphorylation on Ser/Thr/Tyr in Bacillus subtilis. Proteomics 7, 3509-3526. 

As is often the case, tissue-specific control mechanisms operate to optimise adaptation to particular conditions. For example, muscle contraction requires an increase in cytosolic calcium ion concentration (see Section 7.2.1, Figure 7.4). During exercise when energy generation needs to be increased, or from a more accurate metabolic point of view, when the ATP-to-ADP ratio falls rapidly, and the accompanying rise in [Ca2 + ] activate (i) glycogen phosphorylase which initates catabolism of... 

Longer lasting control of mineral metabolism is achieved by steroid hormones elaborated by the adrenal cortex and by synthetic analogues. Besides their actions on gluconeogenesis, glycogen deposition, protein metabolism and sexual characteristics, the corticosteriods influence calcium metabolism and the control of water and electrolyte equilibria, so that profound changes accompany their administration. 

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