CONDUCTION BETWEEN ISOLATED RABBIT PURKINJE AND VENTRICULAR MYOCYTES COUPLED BY A VARIABLE RESISTANCE

Conduction at the Purkinje-ventricular junction (PVJ) demonstrates uni directional block under both physiological and pathophysiological cond itions. Although this block is typically attributed to multidimensiona l electrotonic interactions, we examined possible membrane-level contr ibutions using single, isolated rabbit Purkinje (P) and ventricular (V ) myocytes coupled by an electronic circuit. When we varied the juncti onal resistance (R-j) between paired V myocytes, conduction block occu rred at lower R-j values during conduction from the smaller to larger myocyte (115 +/- 59 M Omega) than from the larger to smaller myocyte ( 201 +/- 51 M Omega). In Purkinje-ventricular myocyte pairs, however, b lock occurred at lower R-j values during P-to-V conduction (85 +/- 39 M Omega) than during V-to-P conduction (912 +/- 175 M Omega), although there was little difference in the mean cell size. Companion computer simulations, performed to examine how the early plateau currents affe cted conduction, showed that P-to-V block occurred at lower R-j values when the transient outward current was increased or the calcium curre nt was decreased in the model P cell. These results suggest that intri nsic differences in phase 1 repolarization can contribute to unidirect ional block at the PVJ.