Insulin receptor autophosphorylation in cultured myoblasts correlates to glucose disposal in Pima Indians

In a previous study [Youngren, J. F., I. D. Goldfire, and R. E. Pratley. Am . J. Physiol. 273 (Endocrinol. Metab. 36): E276-E283, 1997] of skeletal mus cle biopsies from insulin-resistant, nondiabetic Pima Indians, we demonstra ted that diminished insulin receptor (IR) autophosphorylation correlated wi th in vivo insulin resistance. In the present study, to determine whether d ecreased IR function is a primary trait of muscle, and not secondary to an altered in vivo environment, we cultured myoblasts from 17 nondiabetic Pima Indians in whom insulin-stimulated glucose disposal (M) was measured durin g hyperinsulinemic-euglycemic glucose clamps. Myoblast IR autophosphorylati on was determined by a highly sensitive ELISA. IR autophosphorylation direc tly correlated with M (r = 0.56, P = 0.02) and inversely correlated with th e fasting plasma insulin (r = -0.58, P < 0.05). The relationship between M and IR autophosphorylation remained significant after M was adjusted for th e effects of percent body fat (partial r = 0.53, P < 0.04). The relationshi p between insulin resistance and the capacity for myoblast IR autophosphory lation in nondiabetic Pima Indians suggests that variations in IR-signaling capacity may be intrinsic characteristics of muscle that contribute to the genetic component determining insulin action in this population.