A quantitative histochemical approach to renal transport. I. Aspartate and glutamate.

Renal transport was studied by direct analysis of specific segments of the nephron for the substance transported. Rats were given inulin plus loads of glutamate or aspartate. Glomeruli, six different identified segments, and patches from thin-limb and papillary areas were dissected from individual nephrons in freeze-dried sections. Large amounts of the amino acid (up to 35 mmol/kg) accumulated in segments in which transport is believed to occur. With subthreshold loads, large amino acid increments were confined to earlier proximal segments. With loads above threshold, increases occurred throughout the proximal tubule. The early convoluted tubule probably has less transport activity than the rest of the proximal tubule. Both dicarboxylic amino acids accumulate in large amount when one is given. Aspartate is probably formed within the tubule after a glutamate load. This new histochemical approach may have general applicability for more precise localization of transport cells, for assessing changes in those cells during transport, and for study of structures inaccessible to micropuncture.