Effects of metal ions on the utilization of glucose and on the influence of insulin on it by the isolated rat diaphragm

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Abstract
Insulin increases the uptake of glucose by the isolated rat diaphragm only in the presence of certain metal ions in the added medium. It appears that simultaneous participation of Mg2+ ions and an alkali-metal ion such as Na+ is required for the maximum effect of insulin. Mg2+ ions seem to be essential for maintaining the tissue sensi-tive to insulin. Mg possibly exerts this effect by preserving the integrity of some components of the cell surface by controlling the activity of some enzyme in the system. Ca antagonizes Mg in this respect. The alkali-metal ions have a striking regulatory effect on the basal uptake of glucose by the diaphragm of the rat. In the presence of equivalent amounts of the ions the uptake is highest with Li+ ions and follows the order[image] Li+ > Na+ > K+ = Rb+ > Cs+ In the presence of appropriate amounts of li+ ions the uptake is almost as high as that due to insulin from Gey''s buffer. The ions exert their regulatory effect even when the tissue has permanently lost its ability to respond to insulin. Preincubation of the diaphragm with the alkali-metal ions leads to the uptake of different amounts of glucose when the tissue is subsequently incubated in Geys medium, and the uptake follows the order mentioned above. In the presence of equivalent amounts of the alkali-metal ions, the xylose-space of the diaphragm followed the order Ii+ > Na+ > K+. This suggests that the regulation of the utilization of glucose by the alkali-metal ions is possibly brought about by a regula-tion of the rate of entry of the sugar from the extracellular fluid to the interior of the cell. It is suggested that 2 separate and distinct processes (one, insulin-independent and the other, insulin-dependent) are possibly involved in the utilization of glucose by the rat diaphragm.