Table 1.
Apparent dissociation constants (KD’s) for the binding of different cations to the resting and inactivated state models of the KcsA channel. Mean values given here come from the experiments reported in Figure 3, Figure 4, Figure 5, Figure 6 and Figure 7. Since the estimated KD values are derived from a logarithmic function (Equation (1)), we use the 95% confidence intervals of these values for statistical comparisons, instead of giving mean ± SD values, since only parametric analysis is appropriate on the logarithmic scale for such data. a Significant differences with respect to the resting WT, pH 7 group (p < 0.05). b Significant differences with respect to the same sample without 10 mM TBA (p < 0.05).
| Tested Cations | Sets of Binding Sites Detected | Resting Channel | Inactivated Channel Models | ||||||
|---|---|---|---|---|---|---|---|---|---|
| WT KcsA, pH 7 | WT KcsA, pH 4 | 1–125 KcsA | OPEN KcsA | ||||||
| KD (M) | 95% CI | KD (M) | 95% CI | KD (M) | 95% CI | KD (M) | 95% CI | ||
| Na+ | 1 | 3.3 × 10−3 | (2.5–4.3) × 10−3 | 7.7 × 10−3 | (6.7–8.9) × 10−3 a | 3.1 × 10−3 | (2.9–3.3) × 10−3 | 2.7 × 10−3 | (2.5–2.9) × 10−3 |
| Ba2+ | 1 | 4.0 × 10−9 | (2.7–6.0) × 10−9 | 3.0 × 10−9 | (1.3–6.9) × 10−9 | 9.0 × 10−9 | (3.0–27) × 10−9 | 7.0 × 10−9 | (2.9–17) × 10−9 |
| K+ | 2 | 1.9 × 10−6 | (1.2–2.9) × 10−6 | 9.0 × 10−5 | (7.4–11) × 10−5 a | 2.3 × 10−5 | (2.0–2.7) × 10−5 a | 1.4 × 10−5 | (1.1–1.8) × 10−5 a |
| 2.5 × 10−3 | (1.8–3.5) × 10−3 | 8.4 × 10−3 | (7.5–9.4) × 10−3 a | 1.1 × 10−2 | (9.3–13) × 10−3 a | 1.3 × 10−2 | (1.1–1.5) × 10−2 a | ||
| K+, 10 mM TBA | 2 | 8.0 × 10−4 | (6.4–9.9) × 10−4 b | 6.0 × 10−5 | (3.6–9.9) × 10−5 a | 7.0 × 10−4 | (4.5–11) × 10−4 b | 4.9 × 10−4 | (4.5–5.3) × 10−4 a,b |
| 3.2 × 10−3 | (2.4–4.2) × 10−3 | 2.1 × 10−3 | (1.8–2.5) × 10−3 b | 2.1 × 10−3 | (1.8–2.5) × 10−3 b | 2.4 × 10−3 | (2.1–2.8) × 10−3 | ||
| Rb+ | 2 | 4.0 × 10−6 | (3.5–4.6) × 10−6 | 7.3 × 10−5 | (7.1–7.5) × 10−5 a | 6.0 × 10−6 | (4.5–8.0) × 10−6 | 3.7 × 10−6 | (3.0–4.5) × 10−6 |
| 3.4 × 10−3 | (2.8–4.2) × 10−3 | 7.0 × 10−3 | (6.1–8.0) × 10−3 a | 7.5 × 10−3 | (6.9–8.1) × 10−3 a | 7.4 × 10−3 | (6.7–8.2) × 10−3 a | ||
| Cs+ | 2 | 3.1 × 10−5 | (2.5–3.9) × 10−5 | 9.2 × 10−4 | (8.8–9.6) × 10−4 a | 4.7 × 10−4 | (3.5–6.3) × 10−4 a | 1.7 × 10−4 | (1.4–2.1) × 10−4 a |
| 1.3 × 10−2 | (1.1–1.5) × 10−2 | 1.7 × 10−2 | (1.5–1.9) × 10−2 a | 1.1 × 10−2 | (9.3–13) × 10−3 | 1.6 × 10−2 | (1.3–2.0) × 10−2 | ||