A model study of changes in excitability of ventricular muscle cells: inhibition, facilitation, and hysteresis

facilitation, and hysteresis. Am. J. Physiol. 268 (Heart Circ. Physiol. 37): HllBl-H1194, 1995-A model study was car-ried out to investigate the mechanism of changes in excitabil-ity at long cycle lengths (i.e.,> 1,000 ms), which are respon-sible for various phenomena, including electrotonic inhibition, active facilitation, and hysteresis of excitability in ventricular muscle at slow frequencies of stimulation. Experimental stud-ies suggested that with repetitive activity the inward rectifier potassium current (1~~) is not a passive component of mem-brane response and that the dynamics of Ikl are responsible for the changes in excitability at long cycle lengths. In the present study, we have used new experimental data as the basis to modify the equations for I kl in the ionic model for ventricular muscle of the Luo and Rudy (LR) model. The modified equations for 1 kl incorporate an additional slow gate (s-gate)