Evidence from renal proximal tubules that \documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy}\usepackage{mathrsfs}\setlength{\oddsidemargin}{-69pt}\begin{document}\begin{equation*}{\mathrm{HCO}}_{3}^{-}\end{equation*}\end{document} and solute reabsorption are acutely regulated not by pH but by basolateral \documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy}\usepackage{mathrsfs}\setlength{\oddsidemargin}{-69pt}\begin{document}\begin{equation*}{\mathrm{HCO}}_{3}^{-}\end{equation*}\end{document} and CO ₂

Abstract

Respiratory acidosis, a decrease in blood pH caused by a rise in [CO 2 ], rapidly triggers a compensatory response in which the kidney markedly increases its secretion of H + from blood to urine. However, in this and other acid-base disturbances, the equilibrium CO 2 + H 2 O ⇄ \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}{\mathrm{HCO}}_{3}^{-}\end{equation*}\end{document} + H + makes it impossible to determine whether the critical parameter is [CO 2 ], \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}[{\mathrm{HCO}}_{3}^{-}]\end{equation*}\end{document} , and/or pH. Here, we used out-of-equilibrium \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}{\mathrm{CO}}_{2}/{\mathrm{HCO}}_{3}^{-}\end{equation*}\end{document} solutions to alter basolateral (BL) \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}[{\mathrm{HCO}}_{3}^{-}]\end{equation*}\end{document} , [CO 2 ], or pH, systematically and one at a time, on isolated perfused S2 rabbit proximal tubules. We found that increasing \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}[{\mathrm{HCO}}_{3}^{-}]_{{\mathrm{BL}}}\end{equation*}\end{document} from 0 to 44 mM, at a fixed [CO 2 ] BL of 5% and a fixed pH BL of 7.40, caused \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}{\mathrm{HCO}}_{3}^{-}\end{equation*}\end{document} reabsorption ( J HCO 3 ) to fall by half but did not significantly affect volume reabsorption ( J V ). Increasing [CO 2 ] BL from 0% to 20%, at a fixed \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}[{\mathrm{HCO}}_{3}^{-}]_{{\mathrm{BL}}}\end{equation*}\end{document} of 22 mM and pH BL of 7.40, caused J HCO 3 to rise 2.5-fold but did not significantly affect J V . Finally, increasing pH BL from 6.80 to 8.00, at a fixed \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}[{\mathrm{HCO}}_{3}^{-}]_{{\mathrm{BL}}}\end{equation*}\end{document} of 22 mM and [CO 2 ] BL of 5%, did not affect either J HCO 3 or J V . Analysis of the J HCO 3 and J V data implies that, as the tubule alters J HCO 3 , it compensates the reabsorption of other solutes to keep J V approximately constant. Because the cells cannot respond acutely to pH changes, we propose that the responses of J HCO 3 and the reabsorption of other solutes to changes in \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}[{\mathrm{HCO}}_{3}^{-}]_{{\mathrm{BL}}}\end{equation*}\end{document} or [CO 2 ] BL involve sensors for basolateral \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}{\mathrm{HCO}}_{3}^{-}\end{equation*}\end{document} and CO 2 .