AJP - Renal Physiology, Vol 262, Issue 6 1007-F1014, Copyright © 1992 by American Physiological Society
Regulation of glutamine metabolism in dog kidney cortex: effect of pH and chronic acidosis
A. C. Schoolwerth, B. C. Smith and K. Drewnowska
Department of Internal Medicine, Medical College of Virginia, Richmond 23298.
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.
