EFFECT OF GLANDULAR KALLIKREIN ON DISTAL NEPHRON HCO3- SECRETION IN RATS AND ON HCO3- SECRETION IN MDCK CELLS

Renal kallikrein is localized in the connecting tubule cells and secre ted into the tubular fluid at late distal nephron segments. The presen t experiments were performed to further test the hypothesis that renal kallikrein reduces bicarbonate secretion of cortical collecting duct (CCD). The effect of orthograde injections of pig pancreatic kallikrei n (1 or 3 mu g/ml) into the renal tubular system was investigated. Uri ne fractions (Fr) were collected after a 2-min stop flow. Changes in t he urine fraction with respect to those in free-flow urine samples (Ff ) were related to the respective polyfructosan (Inutest) ratio. Renal kallikrein activity (Fr:Ff kallikrein/ Fr:Ff polyfructosan) increased significantly in the first two urine fractions collected after glandul ar kallikrein administration (kallikrein, 1 mu g/ml, P < 0.05; kallikr ein, 3 mu g/ml, P < 0.01). HCO3- secretion of collecting ducts was sig nificantly reduced dose dependently by orthograde and also reduced by retrograde pig pancreatic kallikrein administration. Release of kinins into the fractions was not affected by the retrograde kallikrein inje ction, even though the kallikrein activity increased considerably (2.2 6 +/- 0.2 vs. 1.55 +/- 0.2, P < 0.05). Adequacy of retrograde injectio ns for delivering substances to the CCD was demonstrated by injecting colloidal mercury and detecting the appearance of this mercury in the renal cortex by transmission electron microscopy. The integrity of the renal tissue after a retrograde ureteral injection was confirmed by s canning electron microscopy. These results confirm and extend previous data (M. Marin-Grez and P. Valles. Renal Physiol. Biochem. 17: 301-30 6, 1994; and M. Marin-Grez, P. Valles, and P. Odigie. J. Physiol. 488: 163-170, 1995) showing that renal kallikrein reduces bicarbonate secr etion at the CCD, probably by inhibiting HCO3- transported by a mechan ism unrelated to its kininogenase activity. Support for this assessmen t was obtained in experiments testing the effect of kallikrein on the luminal bicarbonate secretion of a subpopulation of Madin-Darby canine kidney cells capable of extruding the anion. Kallikrein inhibited HCO 3-/Cl- exchange, and the degree of inhibition was dose dependent. This inhibition occurred in the absence of kininogen in the bathing soluti on.