The convoluted (CPT) and straight (SPT) portions of the renal proximal tubule are susceptible to injury by a wide variety of chemical agents. These agents often affect the CPT or SPT selectively by proposed mechanisms usually attributed to tubular concentration, blood flow delivery patterns and tubuloglomerular feedback responses within the intact kidney. The innate cellular responses to chemical exposures remain virtually unexplored. Hence, the basic goal of this research was to develop an in vitro system that was conducive to examining the innate cellular differences in susceptibility between the CPT and SPT following in vitro exposure to mercuric chloride (HgCl₂), potassium dichromate (K₂Cr₂O₇)$ or hypoxic conditions. A renal cortical slicing technique was developed for these studies to position the CPT and SPT within discrete regions of slices made perpendicular to the cortical-papillary axis. An incubation vessel that could maintain the morophological and biochemical viability of slices for at least 12 hr was also developed. The selective necrosis of CPT induced by K₂Cr₂O₇ or hypoxic exposure, and SPT induced by HgCl₂, observed in vivo was reproduced in renal cortical slices exposed in vitro. Innate cellular uptake mechanisms were then investigated since the tissue distribution of each metal was found to be most concentrated within their respective injured cell type. The transport of PAH, TEA, phosphate, sulfate, glutathione and cysteine were examined as potential mechanisms for selective accumulation of these metals. K₂Cr₂O₇ caused a dose-dependent reduction in the uptake rate of sulfate by cortical slices, while phosphate, PAH, and TEA uptake were unaffected. Although HgCl₂ has a high affinity for sulfhydryl groups its uptake as a complex to glutathione or cysteine was not enhanced. HgCl₂ also had no affect on the uptake rate of PAH or TEA even though both HgCl₂ and K₂Cr₂O₇ were able to reduce the steady state accumulation of these organic substrates.

It is well known that a variety of toxicants can cause damage to the renal proximal tubule. However, the early pathogenesis of these deleterious interactions between a toxicant and this region of the nephron remain poorly understood. Thus, the purpose of this research was to attempt to answer three interrelated questions. First, what are the earliest changes in kidney function and structure after administration of tubule toxicants in vivo? Secondly, how do these structural/functional alterations change over time? Finally, are certain indicators of renal "dysfunction" more sensitive then others to the early stages of proximal tubule injury? The basic experimental approach consisted of injecting laboratory animals with a selective proximal tubule toxicant, and then collecting blood and/or urine at several timepoints after dosing; a variety of renal function indicators were evaluated at each of these timepoints. These included blood urea nitrogen (BUN), the glomerular filtration rate (GFR), and the excretion of glucose, protein, salts, glutathione, enzymes, and other endogenous molecules into the urine. At the termination of the exposure period the kidneys were evaluated histopathologically, and were also assayed for levels of specific enzymes and glutathione. Enzyme histochemistry was used to visualize changes in renal enzyme distribution, and protein electrophoretic methods permitted quantification of urinary proteins. These studies showed that specific markers of renal dysfunction were more sensitive to acute proximal tubule injury than other indicators. Specifically, the urinary excretion of proteins and the brush border membrane marker γ-glutamyl transpeptidase (GGT) were the best indicators of proximal tubule injury. Glucosuria, lysozymuria, and glutathionuria were all less sensitive markers, and changes in BUN or GFR were the poorest indicators of acute proximal tubule injury. These results indicated that the brush border membrane is one of the most susceptible regions of the proximal tubule to acute renal injury. Analysis of urinary protein electrophoresis patterns and kidney histopathology confirmed this hypothesis. This research also demonstrated the progression of the toxicant-tubule interaction over time, and showed that both tubule structure and function may be altered within minutes of administering a nephro-toxicant.