AJP - Renal Physiology, Vol 260, Issue 3 410-F419, Copyright © 1991 by American Physiological Society
Relationships between intracellular amino acid levels and protection against injury to isolated proximal tubules
J. M. Weinberg, I. Nissim, N. F. Roeser, J. A. Davis, S. Schultz and I. Nissim
Department of Internal Medicine, University of Michigan, Ann Arbor.
Metabolism and cellular levels of glycine, alanine, and other relevant
amino acids in proximal tubules were studied during models of acute injury
and protection by glycine. Freeze-clamped, normal rabbit renal cortex was
very rich in glycine (66.8 nmol/mg protein) and glutamate and also had
substantial levels of taurine, alanine, glutamine, serine, and aspartate.
Isolated proximal tubules were severely depleted of all these amino acids
(glycine, 2.1 nmol/mg protein). During 37 degrees C incubation in presence
of alanine, tubules recovered only glutamate to a level approximating that
in vivo (38.8 nmol/mg protein, 15.2 mM). Glycine added to medium at levels
ranging from 0.25 to 2 mM was actively concentrated four- to sixfold by
tubule cells. Two millimolar glycine potently protected tubules from lethal
cell injury induced by hypoxia, antimycin A, or ouabain. Glycine levels of
injured tubules rapidly equilibrated with medium, irrespective of whether
glycine was loaded by preincubation or was added concomitantly with the
injury maneuver. Metabolism of glycine during protection, assessed by
changes in total levels, gas chromatography-mass spectroscopy determination
of the fate of [13C]glycine, and redistribution of label from [3H]glycine
was minimal. The data suggest that glycine plays an essential, constitutive
role in maintenance of tubule cell structural integrity independently of
common metabolic pathways. Intracellular amino acid content is sufficiently
labile for depletion of structurally essential amino acids to potentially
occur in a variety of settings, but, even with severe ATP depletion or Na+
pump inhibition, supplemental glycine is readily available to intracellular
sites of action.
