SPHINGOMYELINASE HAS AN INSULIN-LIKE EFFECT ON GLUCOSE-TRANSPORTER TRANSLOCATION IN ADIPOCYTES

Rat epididymal adipocytes were incubated with 0, 0.1, and 1 mU sphingo myelinase/ml for 30 or 69 min, and glucose uptake and GLUT-1 and GLUT- 4 translocation were assessed. Adipocytes exposed to 1 mU sphingomyeli nase/ml exhibited a 173% increase in glucose uptake. Sphingomyelinase had no effect on the abundance of GLUT-1 in the plasma membrane of adi pocytes. In contrast, 1 mU sphingomyelinase/ml increased plasma membra ne content of GLUT-4 by 120% and produced a simultaneous decrease in G LUT-4 abundance in the low-density microsomal fraction. Sphingomyelina se had no effect on tyrosine phosphorylation of either the insulin rec eptor beta-subunit or the insulin receptor substrate-1, a signaling mo lecule in the insulin signaling pathway. It is concluded that the incu bation of adipocytes with sphingomyelinase results in insulin-like tra nslocation of GLUT-4 to the plasma membrane and that this translocatio n does not occur via the activation of the initial components of the i nsulin signaling pathway.