Table 1. Biophysical properties of ASIC currents in DRG neurones
| Type 1 | Type 2 | Type 3 | |
|---|---|---|---|
| The pH dependence of steady-state inactivation was determined as described in Results, with different conditioning pH and stimulating pH 6. Recovery from inactivation was determined with test pulses to pH 6, separated by intervals of increasing duration at pH 7.4. *Fitting of the type 2 and 3 pH dependence of activation yielded two components. The component with the higher H+ affinity is indicated. For type 2, there was a further current increase at pH < 4; therefore only the fit to the first, most pH-sensitive component is indicated. For type 3, the parameters of the second component are 5.29 ± 0.01 (pH0.5,2), 3.4 ± 0.1 (Hn) and 0.42 (fraction). For comparison, pH0.5 and Hn of activation of recombinant channels were 6.7 ± 0.0 and 2.4 ± 0.1 for ASIC1a, 6.3 ± 0.0 and 3.4 ± 0.5 for ASIC1b, 4.7 ± 0.1 and 1.3 ± 0.5 for ASIC2a, 6.5 ± 0.0 and 2.6 ± 0.6 for ASIC3. pHIn0.5 (pH for half-maximal steady-state inactivation) and Hn were 7.28 ± 0.01 and 5.3 ± 0.6 for ASIC1a, 6.69 ± 0.01 and 5.7 ± 0.6 for ASIC1b, 6.99 ± 0.02 and 4.48 ± 0.71 for ASIC3. The time constant τ of recovery from inactivation was 8.3 ± 1.4 s (ASIC1a), 2.81 ± 0.11s (ASIC1b) and 0.67 ± 0.04s (ASIC3). | |||
| Diameter (μm) | 22 ± 0 | 23 ± 1 | 22 ± 0 |
| Capacitance (pF) | 23.3 ± 1.0 | 25.8 ± 1.8 | 24.2 ± 1.3 |
| IpH6 density (pA pF−1) | 280 ± 38.8 | 44.5 ± 9.4 | 394.9 ± 52.3 |
| Time constant τ of open-channel inactivation pH 6 (s) | 1.54 ± 0.07 | 0.17 ± 0.02 | 0.13 ± 0.01 |
| IpH4/IpH6 | 1.07 ± 0.06 | 4.85 ± 0.78 | 1.68 ± 0.16 |
| pH dependence of activation pH0.5,1 | 6.61 ± 0.01 | 6.02 ± 0.09* | 6.48 ± 0.00* |
| Hn1 | 2.5 ± 0.2 | 2.0 ± 0.3* | 3.1 ± 0.2* |
| pH dependence of steady-state inactivation pHIn0.5 | 7.29 ± 0.01 | 7.26 ± 0.00 | 7.27 ± 0.00 |
| Hn | 4.9 ± 0.5 | 7.2 ± 0.5 | 5.5 ± 0.3 |
| Time constant τ of recovery from inactivation(s) | 10.91 ± 0.00 | 1.44 ± 0.15 | 1.33 ± 0.05 |
| n | 77 | 20 | 34 |