Localization of kallikrein-like activity along a single nephron in rabbits

In order to investigate the presence of renal kallikrein, the localization of kallikrein-like proteolytic activity along a single nephron was determined in rabbits. Single nephrons were dissected into 8 segments under a microscope. Activity was fluorometrically measured with two different substrates (benzoyl-L-arginine ethyl ester: BAEE and prolyl-phenylalanyl-arginine-methylcoumarin amide: MCA). Proteolytic activity could be detected in the early (S1), the middle (S2), and the terminal (S3) portions of the proximal tubule and in the granular portion of the distal tubule (DCTg). With MCA, the specific activity in S1, S2, S3 and DCTg was 0.77 +/- 0.08, 0.28 +/- 0.10, 0.13 +/- 0.05, and 0.27 +/- 0.05 pmoles/microgram/min, respectively. The activity in DCTg was inhibited by aprotinin but that in the proximal tubules was not inhibited. No activity was found in the glomerulus, the thick ascending limb of Henle's loop, the bright portion of the distal tubule, and the light portion of the cortical collecting tubule. The inhibition of the activity by aprotinin in DCTg suggests that intrarenal kallikrein could be localized only in DCTg.