Insulin binding and internalization in cultured fibroblasts from myotonic muscular dystrophy.

The binding and internalization of insulin receptors were investigated in 8 adult form and 6 early-onset myotonic muscular dystrophy (MMD) patients and in age- and sex-matched controls, using cultured skin fibroblasts to avoid the in vivo milieu of donors. The specific insulin binding in the presence of [125I]insulin alone at pH 7.4 and pH 8.0 in MMD patients was not significantly different from that of the controls. The competition curves of insulin binding and the Scatchard plots in MMD and control fibroblasts were similar. Insulin receptor affinity in MMD patients was not different from that in the controls. In the presence of chloroquine, a lysosomotropic agent, the rate of increase in cell-associated radioactivity was similar in both MMD groups and controls. Thus, the normal binding and internalization of the insulin receptors in cultured skin fibroblasts from MMD patients suggest that the insulin receptors are not determined by the pathological genetic factors in MMD. Furthermore, the abnormal insulin binding to freshly isolated cells, reported previously, may be a reflection of environmental factors rather than a genetically determined cellular abnormality in MMD.