Table 1.
Comparison of the effects of α2δ-1 and α2δ-3 subunits on IBa through α1C or α1E-type calcium channels
| α1Cβ2a | α1Cβ2aα2δ-1 | α1Cβ2aα2δ-3 | α1Eβ3 | α1Eβ3α2δ-1 | α1Eβ3α2δ-3 | |
|---|---|---|---|---|---|---|
| IBa density (pA/pF) | 13.8 ± 1.4 (16) | 30.3 ± 6.6* (15) | 28.6 ± 4.9* (21) | 24.4 ± 5.4 (12) | 98.1 ± 20.0*** (10) | 95.4 ± 15.6*** (10) |
| V0.5 activ. (mV) | +5.2 ± 0.1 (16) | −5.0 ± 0.6*** (13) | −3.5 ± 0.5*** (11) | −13.0 ± 1.1 (10) | −14.5 ± 0.2 (9) | −20.1 ± 0.7***, aaa (11) |
| kactiv | 5.4 ± 0.1 | 5.1 ± 0.4 | 5.1 ± 0.4 | 5.6 ± 0.9 | 3.7 ± 0.1 | 4.6 ± 0.6 |
| V0.5 inact. (mV) | −12.5 ± 0.9 (9) | −19.6 ± .3*** (14) | −20.5 ± 0.4*** (8) | −64.4 ± 0.4 (9) | −69.7 ± 0.4*** (11) | −76.2 ± 0.5***, aaa (9) |
| kinact | 11.1 ± 0.7 | 8.5 ± 0.2*** | 8.0 ± 0.3** | 7.1 ± 0.4 | 8.4 ± 0.4* | 9.5 ± 0.4*** |
| A1 (%) | 61.1 ± 3.9 (12) | 73.7 ± 4.5* (11) | 78.1 ± 2.6** (9) | 93.0 ± 2.1 (8) | 97.3 ± 0.5* (10) | 98.5 ± 0.5** (10) |
| τ1 (msec) | 273 ± 24 | 260 ± 19 | 156 ± 10***, aaa | 31.9 ± 5.7 | 23.6 ± 0.9 | 24.1 ± 1.7 |
| τ2 (sec) | 1.16 ± 0.08 | 3.54 ± 0.46*** | 0.90 ± 0.10aaa |
The data are the means ± SEM. The number of experiments performed is indicated in parentheses. The first row compares the average current density for each channel. The second row compares voltage dependence of current activation of different subunit combinations. The ascending part of the I–Vcurve, which is shown in panel a of Figures 4 and 5 was fitted to the Boltzmann function. V0.5 activ and kactiv are the parameters of these fits. The fourth row compares voltage dependence of current inactivation. The steady-state inactivation curves shown in panel b of Figures 4 and 5 were fitted to the Boltzmann function. V0.5 inact and kinact are parameters of Boltzmann fits. The last three rows show the results of fitting the time course of inactivation ofIBa during a 5-sec-long (α1C-derived channels, traces shown in Figure4b) or 300-msec-long (α1E-derived channels, traces shown in Figure 5b) depolarizing pulse to +20 mV. Currents through α1C-derived channels were fitted to a sum of two exponentials. A1 represents the relative amplitude of the current inactivating with the fast time constant τ1. α1E-derived channels were found to inactivate with single time constant. For these channels, 100-A1 represents the relative amplitude of the noninactivating component of the current remaining at the end of the depolarizing pulse (see also Fig. 5b). The significance of the difference was tested using the unpaired Student’st test. Asterisks (*) indicate the statistical significance between α1Cβ2a and α1Cβ2aα2δ-1 or α1Cβ2aα2δ-3 and between α1Eβ3 and α1Eβ3α2δ-1 or α1Eβ3α2δ-3. Significant difference between α1Cβ2aα2δ-1 and α1Cβ2aα2δ-3 and between α1Eβ3α2δ-1 and α1Eβ3α2δ-3 is marked by (a).
*p < 0.05; **p < 0.01; ***p < 0.001; aaap < 0.001.