Effect of insulin on the lysosomal function of rat aortic smooth muscle cells and subcutaneous fibroblasts in tissue culture.

Extracellular and intracellular activities of N-acetyl-beta-glucosaminidase (NAG), a representative lysosomal enzyme, in rat aortic smooth muscle cells and subcutaneous fibroblasts cultured for 6 days with an insulin-enriched (200 microU/ml of insulin) or an insulin-deprived medium were measured. The culture medium was changed every 2 days. The net release of NAG into the medium between the 4th and the 6th day was significantly inhibited in the insulin-enriched culture of both smooth muscle cells and fibroblasts. The inhibition was more marked in the fibroblasts series than in the smooth muscle cell series. On the other hand, the intracellular NAG activity of both cell series was almost similar in the insulin-enriched culture and in the insulin-deprived culture. The results indicate that insulin has an inhibitory effect on the net extracellular release of NAG and, therefore, regulates the lysosomal function in these mesenchymal cells.