Effects of insulin on acetyl-CoA carboxylase in bovine mammary secretory cells

Objectives of this study were to determine effects of insulin on acetyl-CoA carboxylase (ACC) activity and correlate this activity with relative amounts of ACC in MAC-T cells. MAC-T cells were grown in Medium 199 supplemented with fetal bovine serum (5%), cortisol (1 mu g/ml), and insulin (1 mu g/ml). At confuluence, the cells were transferred to 100 mm(2) culture dishes coated with the extracelluar matrix. After 10 h of incubation, the media were replaced with media without fetal bovine serum and the concentration of insulin was lowered to 5 ng/ml. After 24 h, the media were changed to contain the varying concentrations of insulin and incubations continued for 48 h. The addition of insulin resulted in increases in the specific activity of ACC. The maximal effects of insulin on the ACC activity occurred at concentrations of insulin, 1,000 ng/ml. In contrast, the relative change in lactate dehydrogenase (LDH) activity in response to increasing insulin concentrations was minimal as compared to the effects of insulin on ACC. Transblot and enhanced chemiluminescence (ECL) analysis indicated that the increases in ACC activity in MAC-T cells caused by insulin were due to actual increases in amounts of enzyme.