Impaired insulin-induced erythrocyte magnesium accumulation is correlated to impaired insulin-mediated glucose disposal in Type 2 (non-insulin-dependent) diabetic patients

Summary Plasma and erythrocyte magnesium levels were measured by atomic absorption spectrometry in 12 healthy subjects and 12 moderately obese patients with Type 2 (non-insulin-dependent) diabetes mellitus. Basal plasma and erythrocyte magnesium levels were significantly lower in diabetic patients than in control subjects. In vitro incubation in the presence of 100 mU/l insulin significantly increased magnesium erythrocyte levels in both control subjects (p<0.001) and patients with diabetes (p<0.001). However, even in the presence of 100mU/l insulin, the erythrocyte magnesium content of patients with Type 2 diabetes was lower than that of control subjects. The in vitro dose-response curve of the effect of insulin on magnesium erythrocyte accumulation was shifted to the right when red cells of diabetic patients were used, with a highly significant reduction of the maximal effect. Such reduction of the maximal effect of insulin suggests that the impairment of insulin-induced erythrocyte magnesium accumulation observed in Type 2 diabetic patients results essentially from a post-receptor defect. In the diabetic patients, the increase in erythrocyte magnesium levels (calculated as the net increase between basal and 100 mU/l insulin-induced erythrocyte magnesium levels) was negatively correlated with plasma insulin levels (r=–0.86; p<0.001) and with body mass index (r=–0.90; p<0.001); it was positively correlated with the glucose disappearance constant K_g after intravenous glucose injection (r=0.79; p<0.01), with the amount of glucose required to keep euglycaemia despite hyperinsulinaemia in a glucose clamp (r=0.88; p<0.001), and with the metabolic clearance rate of glucose during the clamp (r=0.82; p<0.001). These results demonstrate that insulin-induced erythrocyte magnesium accumulation is impaired in patients with Type 2 diabetes and that such defect is correlated to impaired insulin-mediated glucose disposal in these patients.