FIGURE 9.

Effects of low pH on paracellular ion selectivity in MDCK II cells. (A) Current-clamp of a cell monolayer showed increased transepithelial electrical resistance at apical pH 4. (B) Monovalent ion selectivity was disrupted at pH 5, which was readily reversible upon replacement to pH 7 solutions (inset). A representative monolayer is shown. (C) Tetraionic permeability profile at apical pH 4 (n = 3). (D) Tracer fluxes of ¹⁴C-mannitol and ¹⁴C-ethanolamine at apical pH 4. For each tracer, n = 4.