Kinetics and Rectification of the Slow Inward Current in the Rabbit Sinoatrial Node Cell

抄録

The slow inward current (i_s) in the rabbit sinoatrial node cell was studied by the conventional two-microelectrode voltage clamp technique. When i_s was measured as the difference between two records obtained before and after blocking i_s with D 600, the fully activated current (i_s)-voltage relation was non-linear; the conductance decreased in the negative potential range resulting in an almost constant amplitude of i_s negative to -10 mV. The degree of steady-state activation was about 1 at -5 mV and 0 at -65 mV. The recovery time course of i_s during repolarization was measured by varying the interval between two sequential depolarizing pulses with various holding potentials. The time constant of the exponential recovery time course was about 120 msec at - 40 mV and decreased to about 40 msec at -70 mV. The steadystate conductance of i_s, calculated from the activation and inactivation curves, produced a large hump in the steady-state current voltage relation between -60 and -20 mV, which was not observed in the experiment. When the above kinetics were incorporated, the S-A node model failed to discharge the spontaneous activity. The activation and inactivation curves which can simulate the experimental I-V curve and the action potential were proposed.