Activation of glycolysis by zinc is diminished in hepatocytes from metallothionein-null mice

The influence of hepatic metallothionein (MT) and zinc (Zn) on glycolysis w as investigated in primary cultures of mouse hepatocytes prepared from MT-n ormal (+/+) and MT-null (-/-) mice. Ln MT +/+ mice, a close relationship wa s observed between the Zn concentration in the incubation medium (10-150 mu M), increased MT levels in the cells, and increased glycolysis (accumulati on of lactate + pyruvate) over 24 h, with significant effects seen at physi ological levels of Zn (10-25 mu M). Hepatocytes from MT -/- mice had signif icantly lower basal rates of glycolysis and demonstrated increased glycolys is only at Zn concentrations of 50 mu M or greater. The lactate:pyruvate ra tio was higher in the MT +/+ hepatocytes. The oxidation of endogenous fatty acid (accumulation of the ketone bodies, 3-hydroxybutyrate and acetoacetat e) was initially greater in the MT +/+ hepatocytes, although only MT -/- he patocytes showed increased ketone body production in response to Zn. The S- hydroxybutyrate: acetoacetate ratio was higher in the MT +/+ hepatocytes an d increased with increasing Zn concentrations. Intracellular Zn accumulatio n was 60% greater in the MT +/+ hepatocytes, with approximately 80% of the extra Zn associated with MT. The results implicate MT-associated Zn rather than increased intracellular Zn per se in the regulation of hepatic carbohy drate metabolism.