Insulin binding to myotonic dystrophy fibroblasts

Insulin receptor binding was examined in cultured skin fibroblasts from 10 myotonic dystrophy patients and 10 age- and sex-matched control subjects. The conditions for insulin binding to fibroblasts were optimal and employed HEPES binding buffer, pH 8.0 at 15 °C for 5 h. These conditions correspond to those previously employed with monocytes from MyD subjects. The normalized initial insulin binding capacity showed a decrease of 62% from 5.04 ± 0.28% of the total labeled insulin added/mg protein in the control to 1.93 ± 0.13% in the myotonic dystrophy group ( P < 0.01) due mainly to a marked reduction in high affinity receptors or in receptor affinity. The addition of 1.0 ng/ml of unlabeled insulin produced significant decreases to 3.80 ± 0.25% in the control group and 1.24 ± 0.09% in the MyD group. The results are similar to previously reported findings with monocytes from myotonic dystrophy patients and suggest that a surface membrane defect exists in this disease. However, the conditions that have been employed in the binding procedures in all of the studies, while optimal, are performed at a high pH and low temperature and could have an important bearing on the interpretation of a membrane disorder.