Rapid and slow potassium currents in a sinoatrial node cell model

The sinoatrial node (SAN) model of Demir et al. (Amer. J. Physiol, vol. 266, p. C832-52, 1994) was extended to include two potassium channels. A channel with fast and slow activation components and rapid inactivation (I_Kr) and a channel with slow activation (I_Ks) were investigated by Lei & Brown (1996) and Ono & Ito (1995). New K⁺ current descriptions were incorporated into the model. The simulated action potentials were in agreement with the action potentials recorded by Irasawa et al. (1993). The sum of I_Kr and I_Ks was comparable to the potassium delayed rectifier (I_K) of Demir et al. with the exception that the sum did not totally inactivate. Simulations showed that I_Kr is essential for pacing, as seen in the experiments of Lei & Brown. Voltage clamp experiments were also accurately simulated. In conclusion, two distinct potassium channels were necessary to accurately simulate the K⁺ ionic mechanisms in the rabbit SAN cells