[Role of calcium in the metabolism of carbohydrates].

The role of calcium in the metabolism of carbohydrates is rather complex. It has been shown particularly "in vitro" but also "in vivo", to act on beta cells and peripheral effectors. Cytosolic calcium is determinant for insulin secretion in beta cells. It may be increased by a transfer of extracellular calcium into the intra cellular medium or by a transfer of cytoplasmic organelles into the cytosol. The former is due to the action of glucose or its metabolites. The latter is dependent on the CAMP, probably modulated by the glucose or its metabolites. The action of calcium causes the calmodulin to push on the phosphorylated proteins as does the action of CAMP on the protein kinases. The phosphorylated proteins act on the microtubular and microfilamentous systems; they are responsible for the insulin exocytosis. Calcium interposes a large number of insulin agonists and antagonists. These effects have been proved "in vivo" pathology (hypocalcemia, hyperparathyroidism or hypoparathyroidism) and during intravenous calcium infusion or during administration of products which modify calcium repartition. Calcium on peripheral effectors is considered as a second insulin messenger. But the role of calcium is, in fact, more complex, acting on the affinity of the insulin receptors. Its action on the enzymes could either be agonistic or antagonistic of insulin. The "in vitro" results are also variable.