Figure 7. Electrical isolation of cell layers during a slow wave arises from changes in the membrane resistance of ICC_my during each pacemaker potential.

A, a successive pair of follower potentials. During the interval between slow waves, a current pulse (C) injected into the circular muscle layer (slow waves, B) generates an electrotonic potential in the longitudinal muscle layer. When the same current is injected near the peak of the slow wave, little or no electrotonic transmission is evident in the longitudinal layer. The voltage calibration bar applies to traces A and B. The time calibration bar applies to all traces. The membrane potentials of the circular smooth muscle layer and longitudinal layer were −62 and −61 mV, respectively. The apparent isolation of muscle cell layers during a slow wave can be explained if the membrane resistance of ICC_my fell to a low value during the plateau component of each pacemaker potential. Da, the amplitude of the electrotonic response in longitudinal muscle as a function of pacemaker shunt resistance (R_{ICC-Pacemaker}, see Fig. 1). Injected current (I) was 5 nA and the values of R_C, R_C-IC, R_ICC, R_L-IC and R_L were 2, 3.3, 12.3, 3.3 and 9.3 MΩ, respectively, as before. Db, the amplitude of the electrotonic response in the ICC_my layer as a function of R_{ICC-Pacemaker}. Dc, the amplitude of the pacemaker potential itself in the absence of injected current as a function of pacemaker shunt resistance.