Short-term regulation of glycolysis by insulin and dexamethasone in cultured rat hepatocytes

Abstract

Evidence for a direct metabolic effect of insulin in isolated liver preparations is scarce. The stimulation of glycolysis by insulin previously demonstrated in monolayer cultures of adult rat hepatocytes [(1982) Eur. J. Biochem. 126, 271-278] was further investigated. The degree of stimulation varied with the age of the culture and amounted to 250%, 200%, 500% and 200% of the control value using cells at the culture age of 2 h, 24 h, 48 h, and 72 h, respectively. Half-maximal dose of insulin was 0.1 nM. Maximal stimulation was reached within 5 min and lasted for at least 4 h. Dexamethasone acted both as a long-term and short-term modulator. Long-term pretreatment of the cells with dexamethasone proved necessary to permit insulin action. In addition to this permissive action, pretreatment with dexamethasone reduced the insulin-independent basal glycolytic rate. In short-term experiments dexamethasone decreased the basal glycolytic flux, however, it did not affect the absolute increase in glycolysis brought about by insulin. The half-maximal dose of dexamethasone was 10 nM. The stimulatory effects of insulin may in part be attributed to the activation of pyruvate kinase. Insulin produced a left-shift of the substrate saturation curve, decreasing the K0.5 value for phosphoenolpyruvate.