K depletion stimulates in vivo HCO3 reabsorption in surviving rat distal tubules.

To evaluate whether K depletion enhances in vivo bicarbonate reabsorption (JtCO2) in surviving distal tubules (DT), we compared DT JtCO2 in five-sixths nephrectomized rats (Nx) with and without dietary K depletion (Nx-K). Furthermore, to identify possible mechanisms of increased JtCO2, we perfused inhibitors of proton secretion in both Nx and Nx-K rats. JtCO2 (102 +/- 8 pmol.min-1.mm-1) was significantly increased in Nx-K vs. Nx rats (65 +/- 7 pmol.min-1.mm-1, P < 0.05) but unaffected by 10(-6) M losartan perfusion (94 +/- 6 pmol.min-1.mm-1, P = not significant). Although 10(-5) M Sch-28080 also had no significant effect, 5 x 10(-9) M concanamycin A perfusion significantly decreased JtCO2 in Nx-K rats to 65 +/- 8 pmol.min-1. mm-1 (P < 0.05). Morphometric evaluation and H(+)-ATPase immunogold labeling of Nx-K A-type intercalated cells revealed cellular hypertrophy, elaborated apical microplicae, and enhanced H(+)-ATPase apical polarization. Accordingly, these combined studies confirm that K depletion enhances JtCO2 in surviving DT by stimulating H(+)-ATPase activity, independent of the AT1 receptor.