Intracellular Cystine Loading Causes Proximal Tubule Respiratory Dysfunction: Effect of Glycine

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Abstract
The present study examined proximal tubular respiration in control proximal tubules and proximal tubules loaded with cystine using 2 mmol/L cystine dimethyl ester. Basal oxygen consumption was significantly less in cystine-loaded tubules (20.6 ± 0.5 versus 12.1 ± 0.6 nmol O2·min-1·mg protein-1, p < 0.001). In the presence of 10-4 mol/L ouabain, an inhibitor of the NaK ATPase, oxygen consumption was 10.2 ± 0.7 nmol O2·min-1·mg protein-1 in control tubules and 11.4 ± 1.0 nmol O2·min-1·mg protein-1 in cystine-loaded tubules. Thus, proximal tubular intracellular cystine loading specifically inhibits oxygen metabolism directed toward transport. Compared with control proximal tubules, cystine-loaded proximal tubules also had a lower rate of O2 consumption when the cells were permeabilized to sodium with nystatin and when mitochondrial respiration was uncoupled. Glycine, an amino acid that is cytoprotective to hypoxic proximal tubule injury, ameliorated the repiratory dysfunction observed in cystine-loaded tubules.

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