CO2-stimulated NaCl absorption in the mouse renal cortical thick ascending limb of Henle. Evidence for synchronous Na +/H+ and Cl-/HCO3- exchange in apical plasma membranes.

Abstract

Salt transport processes were evaluated in isolated cortical thick limbs of Henle (cTALH) obtained from mouse kidney. When the external solutions consisted of Krebs-ringer bicarbonate (KRB), pH 7.4, and a 95% O2-5% CO2 gas phase, the spontaneous transepithelial voltage (Ve, mV, lumen-to-bath) was .apprx. 8 mV; the net rate of Cl- absorption .**GRAPHIC**. was .apprx. 3600 pmol s-1 cm-2; the net rate of osmotic solute absorption .**GRAPHIC**. was twice .**GRAPHIC**. and the net rate of total CO2 transport .**GRAPHIC**. was indistinguishable from zero. Net Cl- absorption was accompanied by the net absorption of a monovalent cation, presumably Na+, and net HCO3- absorption was negligible. This salt transport process was stimulated by (CO2 + HCO3-): omission of CO2 from the gas phase and HCO3- from external solutions reduced .**GRAPHIC**. .**GRAPHIC**. and Ve by 50%. Luminal furosemide 10-4 M abolished .**GRAPHIC**. and Ve entirely. The lipophilic carbonic anhydrase inhibitor ethoxyzolamide (10-4 M, either luminal or peritubular) inhibited (CO2 + HCO3-)-stimulated .**GRAPHIC**. .**GRAPHIC**. and Ve by .apprx. 50%; when the combination (CO2 + HCO3-) was absent, ethoxyzolamide had no detectable effect on salt transport. Ve was reduced or abolished entirely by omission of either Na+ or Cl- from external solutions, by peritubular K+ removal, by 10-3 M peritubular ouabain, and by 10-4 M luminal SITS [4-acetamido-4''-isothiocyanatostilbene-2,2''-disulfonic acid]. Ve was unaffected by 10-3 M peritubular SITS or by the hydrophilic carbonic anhydrase inhibitor acetazolamide (2.2 .times. 10-4 M, lumen plus bath). Apparently, CO2 + HCO3--stimulated NaCl absorption in the cTALH involved 2 synchronous apical membrane antiport processes: one exchanging luminal Na+ for cellular H+ and the other exchanging luminal Cl- for cellular HCO3- or OH-, operating in parallel with a (CO2 + HCO3--independent apical membrane NaCl cotransport mechanism.