Fig. 5.

Effect of anion substitution on the whole cell current-voltage (I-V) relationship of Slc26a7 knockout (KO) mouse retinal pigment epithelium (RPE) cells. Cells were dialyzed with N-methyl-d-glucamine (NMDG)-Cl-based internal solution. A–D: currents were recorded before and after replacing 140 mM external NaCl with 140 mM sodium thiocyanate (NaSCN; A, n = 12 cells from 8 mice of both sexes, 4.6–19 wk old), NaNO₃ (B, n = 10 cells from 6 mice of both sexes, 4.6–19 wk old), NaI (C, n = 9 cells from 6 mice of both sexes, 4.6–19 wk old), or Na-isethionate (D, n = 8 cells from 2 mice of both sexes, 8.6–9.2 wk old). Currents were generated by 1-s voltage ramps from −120 mV to +60 mV from a holding potential of −60 mV. Symbols represent means, and bidirectional error bars represent SE. Where not visible, error bars are smaller than the symbol. Ise⁻, isethionate. E: comparison of normalized outward conductance of isolated Slc26a7 KO (open circles) and wild-type (WT; gray squares) mouse RPE cells in the presence of 140 mM external thiocyanate (SCN⁻; KO: n = 12 cells from 8 mice of both sexes, 4.6–19 wk old; WT: n = 8 cells from 3 mice of both sexes, 7–10 wk old), $\text{N}{\text{O}}_3^{-}$ (KO: n = 9 cells from 6 mice of both sexes, 4.6–19 wk old; WT: n = 20 cells from 12 mice of both sexes, 8.7–32.7 wk old), I⁻ (KO: n = 9 cells from 6 mice of both sexes, 4.6–18.9 wk old; WT: n = 8 cells from 4 mice of both sexes, 8.7–32.7 wk old), or Cl⁻ (KO: n = 24 cells from 11 mice of both sexes, 4.6–19.3 wk old; WT: n = 34 cells from 17 mice of both sexes, 7–32.7 wk old). Horizontal lines and error bars represent means ± SD. The difference in conductance between Slc26a7 KO and WT mouse RPE cells was significant in external SCN⁻ (P < 0.0001, 2-way unpaired t test) but not in any of the other anions tested (P > 0.1; ns, not significant). Data for WT mouse RPE cells are from our previously published study on Slc26a7^+/+ mice (10). F: comparison of relative permeabilities for SCN⁻, $\text{N}{\text{O}}_3^{-}$, and I⁻ in isolated Slc26a7 KO (open circles) and WT (gray squares) mouse RPE cells. Permeability ratios (P_A/P_Cl) were calculated from the change in reversal potential (ΔE_rev) produced by replacing 140 mM external Cl⁻ with substitute anions (A) using the Goldman–Hodgkin–Katz equation (Eq. 3). Differences in relative permeability between Slc26a7 KO and WT mouse RPE cells were significant for $\text{N}{\text{O}}_3^{-}$ [KO: 3.8 ± 0.5 (SE), n = 10 cells from 6 mice of both sexes, 4.6–18.9 wk old; WT: 6.3 ± 0.3 (SE), n = 20 cells from 12 mice of both sexes, 8.7–32.7 wk old; P < 0.0002, 2-way unpaired t test] but not for the other anions tested (SCN⁻: KO, n = 12 cells from 8 mice of both sexes, 4.6–19.2 wk old; WT, n = 8 cells from 3 mice of both sexes, 7–10 wk old; I⁻: KO, n = 9 cells from 6 mice of both sexes, 4.6–18.9 wk old; WT, n = 8 cells from 4 mice of both sexes, 8.7–32.7 wk old; P > 0.2, 2-way unpaired t tests). Horizontal lines and error bars represent means ± SD. Data for WT mouse RPE cells are from our previously published study on Slc26a7^+/+ mice (10).