TABLE 1.
Biochemical characterization of ASIC1a mutants
For pH dependence of activation, proton-activated currents were elicited by a drop in extracellular pH from 9.0 to solutions of lower pH. Currents were normalized to the signal obtained at pH 4.0. pH50 is the log of the concentration of protons yielding a current at half-maximum (n = 8–30). For pH dependence of desensitization, whole-cell currents were elicited by extracellular acidification to pH 5.0 from a solution of pH 9.0, 8.0, 7.8, 7.6, 7.4, 7.2, or 7.0. Currents were normalized to the signal obtained at pH 9.0. pHd is the log of the concentration of protons in the preconditioning solution yielding a current at half-maximum, and n is the Hill coefficient estimated for desensitization (n = 9–11). pH50 and pHd are expressed as the mean ± S.E. with a 95% confidence interval (CI). The time constants of desensitization (τd) were estimated by fitting experimental data to a single exponential function as described under “Experimental Procedures” (n = 9–26). Proton-activated currents were elicited by a drop in extracellular pH from 9.0 to 5.0. ND, not determined.
| Mutant | pH50 | CI pH50 | pHd | CI pHd | n | τd |
|---|---|---|---|---|---|---|
| s | ||||||
| C70L | 6.51 ± 0.07 | 6.37–6.56 | 7.39 ± 0.02 | 7.35–7.42 | 11.3 | 1.56 ± 0.17 |
| E79C | 5.51 ± 0.04 | 5.42–5.59 | 7.51 ± 0.02 | 7.47–7.52 | 8.3 | 0.60 ± 0.04 |
| E79C + MTSET | 5.60 ± 0.07 | 5.47–5.73 | ND | ND | ND | 9.75 ± 1.11 |
| E79K | 5.39 ± 0.04 | 5.30–5.48 | ND | ND | ND | 1.39 ± 0.06 |
| E79Q | 5.53 ± 0.07 | 5.39–5.67 | ND | ND | ND | 0.51 ± 0.03 |
| E79D | 6.03 ± 0.07 | 5.85–6.17 | ND | ND | ND | 0.43 ± 0.02 |
| Y282R | 5.64 ± 0.04 | 5.56–5.72 | ND | ND | ND | 1.55 ± 0.20 |
| E416C | 5.72 ± 0.05 | 5.63–5.81 | 7.50 ± 0.02 | 7.46–7.54 | 5.3 | 0.62 ± 0.03 |
| E416C + MTSET | 5.55 ± 0.08 | 5.39–5.70 | ND | ND | ND | 0.63 ± 0.04 |
| E416K | 5.84 ± 0.05 | 5.75–5.93 | 7.48 ± 0.02 | 7.44–7.51 | 9.2 | 1.45 ± 0.08 |
| E416Q | 5.56 ± 0.06 | 5.44–5.67 | ND | ND | ND | 1.04 ± 0.07 |
| E79Q/E416C | 5.51 ± 0.06 | 5.39–5.64 | ND | ND | ND | 0.75 ± 0.06 |
| E79C/E416Q | 5.36 ± 0.03 | 5.29–5.42 | ND | ND | ND | 0.42 ± 0.04 |