Regulation of glutamine metabolism in dog kidney cortex: effect of pH and chronic acidosis

Abstract

To examine the interrelationships of proton compartmentation and ammoniagenesis, experiments were performed in tubules and mitochondria isolated from dog kidney cortex. Tubules were incubated in Krebs-Henseleit buffer at different pH (pHe), and cytosolic pH (pHi) was estimated with the fluorescent probe 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. Mitochondrial pH (pHm) was determined simultaneously in intact tubules by use of dimethyloxazolidine-2,4-dione. Over the pHe range 6.9-7.7, pHi was similar in control and acidotic dogs and linearly related to pHe. At pHe 7.4 in control tubules. pHm was 7.78 +/- 0.07, and varied little over the pHe range of 7.0-7.7. The pH gradient across the mitochondrial membrane rose at acid pHe. pHm was more alkaline when estimated in tubules from acidotic dogs compared with controls. Ammonium and glucose productions from glutamine were inversely related to pHe and pHi in tubules from both control and acidotic animals and were higher in acidosis. In contrast, ammonium production by isolated mitochondria did not vary as pHe was altered. Enzyme fluxes, calculated from metabolite changes, demonstrated that glutamate dehydrogenase (GDH) flux was altered. Enzyme fluxes, calculated from metabolite changes, demonstrated that glutamate dehydrogenase (GDH) flux was inversely and glutaminase (PDG) flux was linearly related to pHe. Ammonium production was significantly greater in mitochondria from acidotic dogs because of accelerated flux through PDG but not GDH. The present study demonstrates significant difference between proton compartmentation and regulation of ammoniagenesis in kidneys from acidotic dog compared with rat.