TABLE I.
Model Rate Constants
| Rate Constants | Kv4.3 | Kv4.3/DPPX | Kv4.3/DPPX-TEA |
|---|---|---|---|
| s−1 | G0 | G1 | G2 |
| α0 | 550 | 550 | 550 |
| β0 | 9 | 5 | 9 |
| kco | 500 | 600 | 600 |
| koc | 1100 | 1100 | 990 |
| koi | 200 | 200 | 200 |
| kio | 90 | 90 | 90 |
| kci | 30 | 60 | 120 |
| kic | 0.1 | 0.2 | 0.16 |
| kis | 15 | 15 | 15 |
| ksi | 7.5 | 7.5 | 7.5 |
| f | 0.3 | 0.3 | 0.3 |
| kics | 2.5 | 1 | 3 |
| kcsi | 1.4 | 1.5 | 0.75 |
The model has been modified from Bähring et al. (2001). The voltage-dependent rates are of the form α = α0·exp[zaV/(RT/F)] for the forward rates and β = β0·exp[zbV/(RT/F)] for the backward rates, where α0 and β0 are the rates at 0 mV and za and zb are the equivalent charges moving up to the transition state. Channel opening and closing are defined by kco and koc, respectively, open-state inactivation by koi and kio, and closed-state inactivation by kci and kic. A deep-inactivated state, defined by kics and kcsi, has been introduced to reproduce the biexponential recovery from inactivation. All closed states are connected to inactivated states via kci and kic. The coupling of activation and inactivation is defined by an allosteric factor f. Transition leading from IO to IS is defined by kis and ksi. Column G0 represents the gating model for Kv4.3 homotetramers, G1 for Kv4.3/DPPX heteromultimers, and G2 the gating of these heteromultimers at saturating TEA concentrations of the high affinity binding site. Total conductance as a function of TEA concentration and the relative contribution of homo and heteromultimers are computed with the following expression:
where Kd1, Kd2, and Kd3 are the affinity dissociation constants obtained experimentally, and r represent the percentage of Kv4.3/DPPX present in the membrane.
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