To use the applet, click the Start button to initiate the simulation and the Reset button to return the parameters to their initial values. Check the box for each variable to plot it in the window.
In 1991 Luo and Rudy (1991) presented an ionic model (LR-I) for the cardiac action potential in guinea pig ventricular cells based on the Beeler-Reuter model but updated to include more recent experimental results. They reformulated the opening and closing rate coefficients for the sodium current from the BR-model, making these faster processes, and added three new currents: one plateau potassium current, one background current with constant conductance, and an additional potassium current with a gate variable that can be approximated by its steady-state value due to a small time constant. They retained the Beeler-Reuter formulation for the slow inward calcium current as well as the time-dependent potassium current. However, they allowed the possibility of changing the extracellular potassium concentration. In total, phase one of the Luo-Rudy model (LR-I) describes six different currents and uses nine variables, one of which is approximated by its steady state and is replaced by a function, so that only eight variables are needed in the calculation.
The LR-I model, in contrast to the Beeler-Reuter model, produces an action potential with a faster upstroke more consistent with experimental observations. Thus, compared with the Beeler-Reuter model, it is expected that the faster sodium dynamics will result in action potentials produced by the LR-I model will be longer and with higher depolarization. Therefore, it is expected that this model will be more excitable and will be able to produce excitations at shorter S1-S2 coupling intervals. It is also anticipated that the change in action potential duration at shorter S1-S2 coupling intervals will be smaller than for the Beeler-Reuter model, and indeed this is the case, as can be seen by varying the stimuli timings in the applet.
Luo CH, Rudy Y. (1991) Circ Res 68, 1501-1526.,