Oxygen dependence of cellular metabolism: The effect of O2 tension on gluconeogenesis and urea synthesis in isolated rat hepatocytes

Abstract

The dependencies of gluconeogenesis and urea synthesis on oxygen concentration were measured in suspensions of isolated rat hepatocytes and compared with the O₂ dependence of cellular energy supply (reduction of cytochrome c, respiratory rate, mitochondrial [NAD⁺]/[NADH], lactate production, and [ATP]/[ADP][Pi]). As the oxygen concentration was decreased, production of both glucose and urea declined; the changes were observable at 20 μM oxygen and below, with the apparent K_m values for both processes of near 5 μM. The similar dependence of gluconeogenesis and urea synthesis on oxygen concentration indicates that the two pathways have equal access to the cellular ATP supply, i.e., there is no evidence that either pathway is preferentially turned off to spare ATP for the other. The cellular energy state had an oxygen dependence similar to that of glucose and urea synthesis. It is suggested that the behavior of gluconeogenesis and urea production is a reflection of homeostatic regulation of cellular metabolism which is designed to respond to changes in [ATP]/[ADP][Pi].