Effect of back reactions with z

_{β} < z

_{α}.

*α*_{0}= 1,

*β*_{0}= 1,

*z*_{α} = 0.85,

*z*_{β} = 0.17 (arbitrary units). From Eqs. A3 and A4,

≈−40 mV and

*V*_{1/2} ≈ 42 mV. (A) Symbols, simulated

*t*_{d}*(V)* and

*S*_{Max}*(V)*. Thick lines, predicted delay or maximum slope without deactivation. Deactivation shortens the delay and reduces the maximum slope for all but the highest voltages. Thin line (delay), fit of

*t*_{d}*(V)* with the four-step model (Eq. 4), apparent

*α*_{0}= 1.7 and z

_{α} = 0.66. Thin line (slope), fit of

*S*_{max}*(V)* with Eq. 3 and z

_{α} forced to the value from the delay fit. The resulting fit is not very good,

*S*_{max}*(V)* is somewhat steeper. (Inset) Experimental example.

*t*_{d}*(V)* and

*S*_{Max}*(V)* relations (delay fit,

*α*_{0}= 6.7 s

^{−1},

*z*_{α} = 0.57; slope fit,

*z*_{α} forced to 0.57). (B) Fits of simulated

*P*_{O}(t) rise (thick lines) with Eq. 2 and the apparent parameters from the

*t*_{d}*(V)* fit (thin lines). At 0 mV, the fit amplitude is larger, and at 30 mV it is smaller than the peak P

_{O}. At 90 mV, Eq. 2 needs to be strongly upscaled to fit the early rising phase of P

_{O}. (Inset) Experimental example, as in A. When fitting the recorded current rise with Eq. 2 and the parameters from the delay fit, the fit amplitudes at 0 and 30 mV are smaller, and at 90 mV larger than the peak current.

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