Direct quantitation of amino acid transport and metabolism in segments of individual nephrons.

A new approach to amino acid transport in kidney is described which may be useful for study of renal transport in general. The amino acid is given in threshold and above threshold loads along with inulin as a glomerular filtrate marker. The kidney is quickly frozen at --60 degrees. Frozen 16 mum sections are dried at --40 degrees, and identified parts of single nephrons are analyzed for amino acid given, certain metabolites and inulin. The relationship of amino acid to inulin along the tubule is used to indicate changes relative to the glomerular filtrate. With either aspartate or glutamate loads, both amino acids accumulate to high levels in segments in which transport is believed to take place (proximal convoluted and straight tubules). Glutamine also accumulates to a high degree, but only in the proximal straight tubule.