Repolarizing K+ currents I-TO1 and I-Ks are larger in right than left canine ventricular midmyocardium

Background-The ventricular action potential exhibits regional heterogeneity in configuration and duration (APD). Across the left ventricular (LV) free wall, this is explained by differences in repolarizing K+ currents. Howeve r, the ionic basis of electrical nonuniformity in the right ventricle (RV) versus the LV is poorly investigated. We examined transient outward (I-TO1) , delayed (I-Ks, and I-Kr), and inward rectifier K+ currents (I-Ki) in rela tion to action potential characteristics of RV and LV midmyocardial (M) cel ls of the same adult canine hearts. Methods and Results-Single RV and LV M cells were used for microelectrode r ecordings and whole-cell voltage clamping. Action potentials showed deeper notches, shorter APDs at 50% and 95% of repolarization, and less prolongati on on slowing of the pacing rate in RV than LV. I-TO1 density was significa ntly larger in RV than LV, whereas steady-state inactivation and rate of re covery were similar. I-Ks tail currents, measured at -25 mV and insensitive to almokalant (2 mu mol/L), were considerably larger in RV than LV. I-Kr, measured as almokalant-sensitive tail currents at -50 mV, and I-K1 were not different in the 2 ventricles. Conclusions-Differences in K+ currents may well explain the interventricula r heterogeneity of action potentials in M layers of the canine heart. These results contribute to a further phenotyping of the ventricular action pote ntial under physiological conditions.