Biophysical properties and G-protein modulation of calcium channel α1 subunits
| System | α1B | α1E(rbEII) | α1Elong | α1bEEEE | α1BΔN1–55 | |
|---|---|---|---|---|---|---|
| IBa slope conductance (μS) | Oocytes | 36.6 ± 3.3 (7) | 17.6 ± 3.4 (8) | 15.6 ± 3.9 (7) | 10.7 ± 1.1 (7) | 28.1 ± 3.1 (15) |
| V50 for control IBa activation (mV) | Oocytes | −8.5 ± 1.3 (7) | −1.2 ± 1.7 (8) | 0.2 ± 1.4 (7) | 2.8 ± 0.7 (7) | −5.3 ± 1.8 (7) |
| V50 forIBa activation plus quinpirole (mV) | Oocytes | −1.0 ± 1.7* (7) | −0.8 ± 1.5 (8) | 3.8 ± 1.3* (7) | 7.0 ± 0.9* (7) | −6.2 ± 1.8 (7) |
| % inhibition by quinpirole at 0 mV | Oocytes | 49.6 ± 3.0 (13) | −3.7 ± 1.5** (11) | 25.8 ± 1.5** (14) | 30.2 ± 3.6** (9) | −1.1 ± 0.9** (18) |
| Maximum controlIBa (+GDPβS) (pA.pF−1) | COS-7 | 24.4 ± 4.3 (5) | 26.1 ± 5.2 (5) | 17.9 ± 3.4 (7) | 22.3 ± 3.7 (7) | 26.5 ± 6.1 (15) |
| τact in control cells (+GDPβS) at −10 mV (msec) | COS-7 | 7.9 ± 1.9 (5) | 4.6 ± 0.6 (5) | 3.3 ± 0.4 (7) | 6.5 ± 1.2 (7) | 7.7 ± 1.3 (15) |
| τact with Gβ1γ2 at −10 mV (msec) | COS-7 | 33.6 ± 4.6 (9) | 7.0 ± 1.1** (6) | 16.7 ± 1.6** (10) | 18.4 ± 1.8** (10) | 6.3 ± 0.7** (5) |
| Facilitation by depolarizing prepulse (P2/P1 at −10 mV) | COS-7 | 5.3 ± 2.0 (8) | 1.0 ± 0.1** (8) | 1.8 ± 0.6** (7) | 1.9 ± 0.3** (8) | 1.1 ± 0.03** (5) |
The parameters determined for the different α1 constructs (co-transfected with β2a and α2-δ) were measured as described in Materials and Methods, and in the legends to Figures 2 and 3. The statistical significances of the differences between the V50 data for the I–V plots in the presence and absence of quinpirole were determined by paired t test, *p < 0.005. The data for quinpirole inhibition ofIBa were determined from time course studies at 0 mV. The statistical significance of the differences in % inhibition by quinpirole, τact in the presence of Gβ1γ2, and facilitation ratio in the presence of Gβ1γ2, for all the constructs compared with α1B, is indicated by **p < 0.01 (Student’s t test). There are no statistically significant differences between α1Elong and α1bEEEE for these parameters (p > 0.05). The differences between other parameters, not relating to G-protein modulation, were not examined.