Transport activities involved in intracellular pH recovery following acid and alkali challenges in rat brain microvascular endothelial cells

Transport activities involved in intracellular pH (pHi) recovery after acid or alkali challenge were investigated in cultured rat brain microvascular endothelial cells by monitoring pHi using a pH-sensitive dye. Following relatively small acid loads with pHi ∼ 6.5, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{HCO}}_3^ - $$\end{document} influx accounted for most of the acid extrusion from the cell with both Cl−-independent and Cl−-dependent, Na+-dependent transporters involved. The Cl−-independent component has the same properties as the NBC-like transporter previously shown to account for most of the acid extrusion near the resting pHi. Following large acid loads with pHi < 6.5, most of the acid extrusion was mediated by Na+/H+ exchange, the rate of which was steeply dependent on pHi. Concanamycin A, an inhibitor of V-type ATPase, had no effect on the rates of acid extrusion. Following an alkali challenge, the major component of the acid loading leading to recovery of pHi occurred by \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{{\text{Cl}}^ - } \mathord{\left/ {\vphantom {{{\text{Cl}}^ - } {{\text{HCO}}_3^ - }}} \right. \kern-\nulldelimiterspace} {{\text{HCO}}_3^ - }}$$\end{document} exchange. This exchange had the same properties as the AE-like transporter previously identified as a major acid loader near resting pHi. These acid-loading and acid-extruding transport mechanisms together with the Na+, K+, ATPase may be sufficient to account not only for pHi regulation in brain endothelial cells but also for the net secretion of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{HCO}}_3^ - $$\end{document} across the blood–brain barrier.