Characteristics of the rectifying properties of the sino-atrial node cell of the rabbit.

After confirming the region of the sino-atrial (S-A) node by its characteristic action potential, man-made strands including the pacemaker region of the rabbit heart were prepared and simple cable theory analysis performed. The estimated gamma was 828 mum in Tyrode. 2. The single sucrose gap method was employed to conduct both the current-clamp experiment and the voltage-clamp experiment. In both methods outward-going and inward-going rectification were observed. 3. The existence of a positive after-potential in the case of the current-clamp experiment and of an outward current tail in the case of the voltage-clamp experiment after cessation of cathodal pulses suggests that the outward-going rectification is due to the increase of K conductance. 4. The slowly developed inward-going rectification was always accompanied with a decrease of membrane resistance. It is unlikely that change in K conductance is solely responsible for this rectification. Discussion was made of the possibility that changes in both Na and Cl conductance together with K conductance might be involved.