METABOLIC STUDIES OF RAT RENAL TUBULE CELLS LOADED WITH CYSTINE - THECYSTINE DIMETHYLESTER MODEL OF CYSTINOSIS

The cause of Fanconi syndrome in cystinosis is enigmatic. It has previ ously been shown that renal tubules could be loaded with cystine by in cubating them with cystine dimethylester (CDE), mimicking the biochemi cal hallmark of cystinosis. Such tubules have impaired transport, decr eased whole-cell O-2 consumption, and substrate utilization. In this s tudy, the metabolic disturbances in cystine-loaded renal tubule cells were further characterized, Isolated rat renal tubules were loaded wit h cystine by incubating them with 2 mM CDE for 10 min, This had no sig nificant effect on total ATPase, Na+-K+-ATPase, or the ouabain-insensi tive ATPase activity of renal tissue homogenates from these cystine-lo aded tubules. Intracellular K was significantly lower in the cystine-l oaded tubules (37 +/- 2 versus 47 +/- 3 nEq/mg; P < 0.008). Intracellu lar ATP was reduced by 39% in the cystine-loaded tubules (23.7 +/- 2.4 versus 38.1 +/- 3.3 nmol/mg of protein; P < 0.0025), CDE (2 mM) reduc ed isolated mitochondrial O-2 consumption with glutamate as the substr ate by 66% (4.7 +/- 0.7 versus 13.9 +/- 0.8 nm/min per mg of protein, P < 0.001) but had no effect on mitochondrial O-2 consumption with suc cinate as the substrate. It was speculated that the impaired transport from cystine loading with CDE is secondary to a decrease in energy ge neration.