The Fanconi syndrome, a global renal tubule disorder, is an enigmatic problem which most commonly is associated with cystinosis in pediatrics. The biochemical hallmark of this is excessive intracellular storage of cystine, although the relationship between this and the renal tubule dysfunction is unknown. White blood cells can be loaded with cystine by exposing them to the methylester of it. Extending these studies, we have demonstrated that normal renal tubule cells can be loaded with cystine by incubating them with cystine dimethylester, which results in impaired solute uptake. Further, animals injected with cystine dimethyl-ester for short periods of time did have a number of the elements of the Fanconi syndrome, such as aminoaciduria, increased glucose excretion, and phosphaturia. The treated animals did not have an increase in intracellular cystine, but did have an increase in cysteine. This may have been because of the infrequency of the injections. The overall aim of this proposal is to characterize further this new model of the Fanconi syndrome. To examine whether prolonged and continous infusions will result in greater solute losses and the intracellular accumulation of cystine, chronic intravenous catheters will be placed in rats and cystine dimethylester will be continuously infused. Renal ATP levels will also be measured in these animals. Isolated renal tubules and brushborder membranes will be prepared from these animals to study whether an effect on transport in vitro can be demonstrated. The effect of cystine dimethylester on the transport characteristics of amino acids and sugar by isolated renal tubules will be examined. The effect of this ester on transport by tubules isolated from developing animals will be studied since immature tissue is resistant to other agents which induce the Fanconi syndrome. Because cystine dimethylester impairs transport in intact renal tubule cells, the effect of this compound on brushborder membrane uptake will also be examined to see if the site of this effect is in the membrane. Since the Fanconi syndrome is often associated with disorders of intermediary metabolism, the effect of cystine dimethylester on 02 consumption, substrate utilization, ATP levels, gluconeogenesis, and ammoniagenesis by isolated tubules will be studied. From these data, insights into the relationship of increased cystine and renal tubule dysfunction should be forthcoming.
