We examined whether
H(+)-ATPase, H(+)-K(+)-
ATPase, and or Na+/H+ exchange mediates increased distal tubule acidification in animals with chronic metabolic
alkalosis using pharmacological inhibitors of these H+ transporters in in vivo-perfused tubules of anesthetized rats. Chronic metabolic
alkalosis was induced with
furosemide followed by minimum
electrolyte diet and HCO3
drinking water. The reduction in net HCO3 reabsorption was greater in distal tubules of alkalotic compared to control animals perfused with Schering 28080 to inhibit H(+)-K(+)-
ATPase (-6.4 +/- 0.9 vs. -1.4 +/- 0.5 pmol/mm.min-1, P < 0.02) and with
EIPA to inhibit Na+/H+ exchange (-11.1 +/- 1.7 vs. -6.6 +/- 0.9 pmol/mm.min-1, P < 0.01) but was similar in distal tubules of alkalotic and control animals perfused with bafilomycin to inhibit
H(+)-ATPase. The greater reduction of distal tubule net HCO3 reabsorption in alkalotic compared to control animals induced by
EIPA was eliminated by systemic infusion of the
endothelin receptor antagonist bosentan (-4.6 +/- 0.7 vs. -4.4 +/- 0.7 pmol/mm.min-1, P = NS) but the greater reduction induced by Schering 28080 persisted. Urine
endothelin-1 (ET-1) excretion was higher in animals with maintained
alkalosis (164.5 +/- 23.7 vs. 76.6 +/- 10.8 fmol/day, P < 0.03), but decreased following KCl repletion to a value (86.7 +/- 10.0 fmol/day, P < 0.02 vs. respective before-KCl value) that was not different from that for KCl-repleted control animals (79.9 +/- 8.7 fmol/day, P = NS vs. KCl-repleted alkalotic animals). The data support that augmented distal tubule acidification in alkalotic animals is due to increased H(+)-K(+)-
ATPase and Na+/H+ exchange activity, the latter stimulated by endogenous
endothelins.