FIGURE 1.

Extracellular Cl⁻ does not affect pH sensitivity or selectivity of ASIC1a. A, representative currents evoked by stepping from pH 8 to the indicated pH test solutions in CHO cells transfected with ASIC1a. Solutions consisted of high (131–148 mm) or low (11 mm) Cl⁻ (Cl⁻ was replaced with MeSO₃⁻). Plot at right is the mean current density evoked by pH 5 for groups of cells (n = 42–49). B, pH dose-response curves for activation in the above solutions. Data are acquired by stepping from pH 8 to the indicated test solutions and are normalized to the peak currents evoked by pH 5 (n ≥ 10). A similar result was obtained in solutions containing 0 mm Cl⁻ (data not shown). Note the asymmetry of the curves; thus they did not fit well to the Hill equation. C, pH dose-response curves for steady-state desensitization in the above solutions. Data are acquired by varying the conditioning pH and then stepping to pH 5 test solutions and are normalized to the currents evoked by stepping from pH 8 to pH 5 (n ≥ 5). Lines are fits of the Hill equation. D, overlay of currents evoked by pH 6 during steps to various membrane potentials in extracellular NaCl or NaMeSO₃ solutions. The internal solution was KCl. E, current versus voltage curves for the data in D. Data obtained in MeSO₃⁻ lie on top of those obtained in Cl⁻. The reversal potential for both curves is ∼50 mV, indicating Na⁺ selective permeability over K⁺ (n = 4).