Potential role for gluconeogenesis in pyruvate stimulation of H+ transport by turtle urinary bladder

Abstract

The rate of H+ transport (JH) by turtle bladder is coupled to glucose metabolism by the pentose shunt and can be stimulated in bladders depleted of endogenous substrate by pyruvate. In order to define the pathway of pyruvate metabolism that results in an increment in JH, the effect of an inhibitor of gluconeogenesis, 3-mercaptopicolinic acid (MPL), was examined on pyruvate stimulation of JH, glucose formation, and the rate of pyruvate metabolism. Bladders were incubated in substrate-free media for 18 h. Then either pyruvate or glucose was added to the medium in the presence or absence of 10 μM MPL. The rate of JH was determined by the pH stat technique, Na+ transport from the short-circuit current, and pyruvate metabolism was determined from the rate of 14CO2 production from [14C]pyruvate. The increase in JH in control bladders after pyruvate addition, 155.8 ± 13.6 μmol·h-·g dry wt-, was greater than in MPL-treated bladders, 59.7 ± 13.1 μmol·h-·g dry wt- (P < 0.01). Glucose appearance in the incubation medium was also greater in controls, 0.83 ± 0.16 vs. 0.22 ± 0.07 μmol·h-1·g dry wt- (P < 0.01). MPL had no effect on JH stimulation by glucose. Pyruvate stimulation of Na+ transport, which does not require gluconeogenesis, was not affected by MPL. MPL reduced only that moiety of pyruvate metabolism associated with H+ transport. MPL probably does not inhibit nongluconeogenic pathways of pyruvate metabolism or glucose metabolism itself. From these studies it is suggested that pyruvate stimulation of JH requires gluconeogenesis, and that in part it is the metabolism of glucose that is required for increased rates of JH. 3-mercaptopicolinic acid; acetazolamide; pyruvate metabolism; short-circuit current Submitted on November 13, 1979 Accepted on April 29, 1980