Localization of active and inactive kallikrein (kininogenase activity) in the microdissected rabbit nephron

Active and total (trypsin-activated) kallikrein were measured in discrete segments of the nephron by their kininogenase activity. The kinins generated were measured by radioimmunoassay and the amount of inactive kallikrein was calculated as the difference between total and active kallikrein. Single nephrons from collagenase-treated rabbit kidneys (N = 12) were microdissected and divided into eight segments: (1) glomerulus; (2) proximal convoluted tubule; (3) cortical thick ascending limb; (4) bright portion of distal convoluted tubule; (5) granular portion of distal convoluted tubule; (6) granular portion of cortical collecting tubule; (7) light portion of cortical collecting tubule; and (8) medullary collecting tubules. After pooled segments (approximately 50 nephron segments in each assay) were homogenized and treated with deoxycholic acid, active and total kallikrein were measured and inactive kallikrein was calculated. Active and inactive kallikrein were localized in granular portions of the distal and cortical collecting tubule, which contains more than 85% of the active and inactive kallikrein found in the total microdissected nephron. Little or no kallikrein was detected in other segments, including the bright portion of the distal segment which has the macula densa. The discrete localization of active and inactive kallikrein suggests a specific role for renal kallikrein in these nephron segments.