Effects of Cd2+ on the amplitude and voltage dependence of the various homomeric and heteromeric channels
| Channel | V50 | V50Cd | ICda |
| mV | mV | ||
| WT Q2 | −20.0 ± 2.3 (23) | −22.7 ± 2.4 (23) | 0.80 ± 0.04 (23) |
| S195C Q2 | 1.4 ± 1.6b (7) | — | 0.09 ± 0.02b (7) |
| R198C Q2 | −0.8 ± 2.6b (7) | — | 0.09 ± 0.02b (7) |
| R201C Q2 | — | — | 0.12 ± 0.02b (6) |
| C106A Q2 | −35.2 ± 1.4b (5) | −35.9 ± 4.0b (5) | 0.92 ± 0.10 (5) |
| C242A Q2 | −31.1 ± 1.5b (6) | −29.8 ± 1.5b (6) | 0.92 ± 0.04 (6) |
| C242A-S195C Q2 | −6.8 ± 0.7 (7) | — | 0.10 ± 0.03b (7) |
| C242A-R198C Q2 | 5.2 ± 0.3 (6) | — | 0.07 ± 0.01b (6) |
| C242A-R201C Q2 | — | — | 0.12 ± 0.02b (5) |
| C106A-S195C Q2 | −15.2 ± 0.5 (5) | −28.9 ± 1.1 (5) | 0.64 ± 0.05c (5) |
| C106A-R198C Q2 | −9.4 ± 0.3b (5) | −22.3 ± 0.3 (5) | 0.71 ± 0.08c (5) |
| C106A-R201C Q2 | — | — | 0.72 ± 0.07c (5) |
| WT Q2/WT Q3 | −34.3 ± 4.3 (7) | −32.4 ± 4.2 (7) | 0.98 ± 0.21 (7) |
| R198C Q2/WT Q3 | −18.8 ± 1.5b (7) | — | 0.16 ± 0.05b (7) |
| C106A-R198C Q2/WT Q3 | −23.8 ± 3.8b (6) | −25.3 ± 3.5b (6) | 0.97 ± 0.03 (6) |
| R198C Q2/C136A Q3 | −12.2 ± 0.3b (7) | — | 0.28 ± 0.07b (7) |
| WT Q2/C136A Q3 | −38.8 ± 3.0 (6) | −40.1 ± 3.2 (6) | 0.96 ± 0.14 (6) |
| Con WT Q2 | −26.3 ± 1.3 (7) | −24.6 ± 1.7 (7) | 0.99 ± 0.05 (7) |
| Con Q2 D1 R198C | −19.4 ± 0.7b (7) | −25.7 ± 0.4 (7) | 0.40 ± 0.06b (7) |
| Con Q2 D1 R198C, D2C106A | −21.1 ± 0.8 (7) | −30.6 ± 0.6 (7) | 0.32 ± 0.05b (7) |
| Con Q2 D1 C106A, R198C | −23.8 ± 0.6 (7) | −25.5 ± 0.4 (7) | 0.75 ± 0.16 (7) |
| Channel | V50 | V50Cd | ICda |
| mV | mV | ||
| WT Q2 | −20.0 ± 2.3 (23) | −22.7 ± 2.4 (23) | 0.80 ± 0.04 (23) |
| S195C Q2 | 1.4 ± 1.6b (7) | — | 0.09 ± 0.02b (7) |
| R198C Q2 | −0.8 ± 2.6b (7) | — | 0.09 ± 0.02b (7) |
| R201C Q2 | — | — | 0.12 ± 0.02b (6) |
| C106A Q2 | −35.2 ± 1.4b (5) | −35.9 ± 4.0b (5) | 0.92 ± 0.10 (5) |
| C242A Q2 | −31.1 ± 1.5b (6) | −29.8 ± 1.5b (6) | 0.92 ± 0.04 (6) |
| C242A-S195C Q2 | −6.8 ± 0.7 (7) | — | 0.10 ± 0.03b (7) |
| C242A-R198C Q2 | 5.2 ± 0.3 (6) | — | 0.07 ± 0.01b (6) |
| C242A-R201C Q2 | — | — | 0.12 ± 0.02b (5) |
| C106A-S195C Q2 | −15.2 ± 0.5 (5) | −28.9 ± 1.1 (5) | 0.64 ± 0.05c (5) |
| C106A-R198C Q2 | −9.4 ± 0.3b (5) | −22.3 ± 0.3 (5) | 0.71 ± 0.08c (5) |
| C106A-R201C Q2 | — | — | 0.72 ± 0.07c (5) |
| WT Q2/WT Q3 | −34.3 ± 4.3 (7) | −32.4 ± 4.2 (7) | 0.98 ± 0.21 (7) |
| R198C Q2/WT Q3 | −18.8 ± 1.5b (7) | — | 0.16 ± 0.05b (7) |
| C106A-R198C Q2/WT Q3 | −23.8 ± 3.8b (6) | −25.3 ± 3.5b (6) | 0.97 ± 0.03 (6) |
| R198C Q2/C136A Q3 | −12.2 ± 0.3b (7) | — | 0.28 ± 0.07b (7) |
| WT Q2/C136A Q3 | −38.8 ± 3.0 (6) | −40.1 ± 3.2 (6) | 0.96 ± 0.14 (6) |
| Con WT Q2 | −26.3 ± 1.3 (7) | −24.6 ± 1.7 (7) | 0.99 ± 0.05 (7) |
| Con Q2 D1 R198C | −19.4 ± 0.7b (7) | −25.7 ± 0.4 (7) | 0.40 ± 0.06b (7) |
| Con Q2 D1 R198C, D2C106A | −21.1 ± 0.8 (7) | −30.6 ± 0.6 (7) | 0.32 ± 0.05b (7) |
| Con Q2 D1 C106A, R198C | −23.8 ± 0.6 (7) | −25.5 ± 0.4 (7) | 0.75 ± 0.16 (7) |
In transfected CHO cells perfused without or with 100 µM Cd2+, currents were evoked from a holding potential of −90 mV by depolarizing steps from −110 to 30 mV in 10-mV increments and repolarized to −60 mV. Conductance–voltage relations were constructed and data were fitted to a single Boltzmann function to yield the V50 values. The values in parentheses correspond to the number of cells examined. Data are expressed as mean ± SEM.
The change in current amplitude was expressed as a ratio ICd of the current measured in the same cell at 30 mV after and before Cd2+ application.
Statistically different from the WT KCNQ2 value, calculated by two-tailed unpaired Student’s t test, assuming equal variances; P < 0.01.
Statistically different from the single KCNQ2 mutant S195C, R198C, and R201C values; P < 0.01.