Glutamic acid decarboxylase in tubules and glomeruli isolated from rat kidney cortex

4-Aminobutyric acid (GABA) synthesis was examined in purified glomeruli and tubules of rat kidney cortex that were incubated in the presence of [2,3-3H2]glutamate. The GABA that was formed was separated from glutamate using anion-exchange resin, and identified by means of an automatic amino acid analyser. In the renal cortex only the tubules were able to form GABA (35.0 nmol mg-1 h-1); the remaining GABA synthesis found in the glomerular preparations can most probably be attributed to a contamination by cortical tubules (9%), as shown by determination of a known tubular marker enzyme (L-gamma-glutamyltransferase). Hydroxylamine (1 mM) and ethanolamine-O-sulfate (10 mM), well-known inhibitors of cerebral GABA formation and GABA catabolism respectively, inhibited renal tubular GABA formation at 100% and 44% respectively.