Kallikrein and prekallikrein in the basolateral membrane of rat kidney tubules. Hypertension

SUMMARY Basolateral membrane (BLM) enriched fraction was isolated from homogenized rat kidney cortex by differential centrifugation. We also obtained a fraction enriched in plasma membrane (PM). The morphology of the Isolated BLM fragments was studied by transmission and freeze fracture electron micros-copy. The relative specific activity of Na+-K+-ATPase was enriched 7-fold, while that of marker enzymes for PM, endoplasmic reticulum, and lysosomes was lower than In the crude bomogenate. There was a 10-fold difference in the ratios of activities of Na+-K+-ATPase to Mg*+-ATPase in the BLM and in the PM enriched fractions. Kallikrein activity was determined with S-2266 substrate and by radioimmunoassay of kinin re-leased. It was low In the BLM fraction prior to adding detergent, but Triton X-100 increased the activity 12 to 16-fold. Both free trypsin and Sepharose 4B-bound insoluble trypsin Increased kallikrein activity 2- to Mold in both the membrane-bound and soluble fractions, probably by activating a prekallikrein. The results were Inter-preted that the kallikrein studied originated from the distal tubular BLM. (Hypertension 3 (suppl II): II-59-II-64, 1981) KEY WORDS • kininogenase • kinlns • prekallikrein activation • kallikrein release • renal enzymes • Na+K+ATPase RENAL distribution of enzymes that releaseor inactivate kinins has been studied by anumber of investigators.1 ' * The glomerulu