voltage dependent transition in a kinetic scheme
A voltage dependent or independent rate for a state transition in a kinetic scheme. The rate is defined by the forward and reverse r-f and r-r (per ms) for zero membrane potential instead of the midpoint potential as in KSRateVhalf. This gives a continuous transition to voltage-independent transitions, so this transition may be used instead of both KSRateVhalf and KSRateTime.
The equivalent gating charge is z, and the position of the activation particle within the transit of the gating particle is gamma: 0 < gamma < 1. An additional quantity r-m imposes a saturation rate for the transition (cf Borg-Graham...). Such saturation may be an appropriate approximation when, for example, a single state is used to represent multiple physical states where the transition in question can only occur from one of the states.
The transition is computed from the forward and reverse rates, alpha and beta, given by:
static final double alpha (double v, double rf, double rr, double z, double gamma, double rm) { double a = rf * Math.exp (ebykt * (gamma) * z * v); a = 1. / (1. / a + 1./rm); return a; }
static final double beta (double v, double rf, double rr, double z, double gamma, double rm) {
double b = rr * Math.exp (-ebykt * (1. - gamma) * z * v); b = 1. / (1. / b + 1./rm); return b; }
where ebykt = e / kT, about 0.042 mV -1.