EVIDENCE FOR CHROMIUM ACTING AS AN ESSENTIAL TRACE-ELEMENT IN INSULIN-DEPENDENT GLUCOSE-UPTAKE IN CULTURED MOUSE MYOTUBES

Previous work from this and other laboratories has suggested that the trace element chromium plays some role in glucose homeostasis. In this study, we sought to characterise an in vitro cell culture model in which the effects of chromium on insulin-dependent glucose uptake could be studied. Mouse C2C12 myoblasts were differentiated to form myotubes in culture in chromium-replete or chromium-poor media. Chromium levels in standard media were 0.56+/-0.01 mu g/l (mean+/-S.E.M.) compared with 0.09+/-0.01 mu g/l in chromium-poor media. In chromium-poor media, insulin-stimulated uptake of radiolabelled glucose was reduced by almost 50% compared with that found in chromium-replete media. This decreased response could be restored by the addition of physiologically relevant (0.3 mu g/l) concentrations of inorganic chromium (P<0.001). The sensitivity of these cells to insulin was reduced dramatically by a reduction in the chromium content of the medium and was again increased (P<0.001) by chromium addition. The concentrations of chromium required to restore the sensitivity to insulin were of the same order as those found physiologically; much higher concentrations of chromium could also stimulate glucose uptake in the absence of insulin but such concentrations were supra-physiological.