REDUCED INWARD RECTIFYING AND INCREASED E-4031-SENSITIVE K-DENSITY INARRHYTHMOGENIC SUBENDOCARDIAL PURKINJE MYOCYTES FROM THE INFARCTED HEART( CURRENT)

Outward Currents in Purkinje Cells from 48-Hour Infarcted Heart. Intro duction: Subendocardial Purkinje myocytes from the 48-hour infarcted h eart (IZPCs) have reduced resting potentials, possibly due to altered inwardly rectifying K+ currents I-K1. Abnormal depolarization-activate d outward K+ currents could contribute to long triangularly shaped act ion potentials of IZPCs. Methods and Results: We used whole cell patch recordings to compare cesium-sensitive I-K1 and 4-aminopyridine (4-AP )-resistant, noninactivating sustained I-K between normal Purkinje myo cytes (NZPCs) and IZPCs, IZPCs showed decreased net membrane currents. Two IZPC groups were distinguished, based on 4-AP-resistant outward K + currents, IZPC-I had isochronal I-K1 current-voltage relations simil ar to NZPCs whereas IZPC-II showed significantly reduced I-K1 and incr eased outward plateau currents, To study the sustained I-K in the pres ence of the Class III antiarrhythmic agent E-4031, a two-pulse protoco l was used to inactivate transient outward currents, followed by step depolarizations. E-4031-sensitive currents were significantly greater in IZPCs at depolarized potentials (> 0 mV), Similar to NZPCs, IZPC E- 4031 currents showed time dependence during depolarization, lack of re ctification at positive steps, and voltage-dependent recovery from blo ck. Conclusion: Decreased I-K1 may account for reduced resting potenti als in IZPCs, E-4031-sensitive currents in NZPCs, unlike those in cani ne ventricular myocytes, are sensitive to 4-AP and are larger in IZPCs .