关键词: 羊心蒲氏纤维, 动作电位, 早后去极化, 低钾, 硝苯吡啶, 利多卡因, I_Ca, I_f

Abstract: Sheep Purkinje fibers were used to investigate early afterdepolarization (EAD) generation and its possible ionic mechanisms with bielectrode voltage clamp technique. Under low K⁺ (2.5mmol/LK⁺) superfusion, two levels (-25 and -55mV) of EAD could be induced on the background of automaticity. The bursts in low membrane level EAD were abolished by nifedipine (2.0μmol/L) whereas those in high membrane level were abolished by lidocaine (10μmol/L) and low temperature (30℃). The quasi-steady-state Ｉ-Ｖ relationship of the background currents obtained with step and ramp voltage clamp showed a negative phase in outward part of the rectification under 5.0mmol/LK⁺ superfusion, while an inward current phase appeared between -55 and -25mV level in the curve under 2.5 K⁺ treatment. Under the condition of EAD generation, the low and high membrane level (-25 and -55mV) of voltage were clamped during the repolarization phase of action potential. On low membrane level of -25mV, a slow inward current similar to Ｉ_Si occurred followed by a slight outward current like I_k, whereas on high level of -55mV, a continued inward current looked like I_f occurred. It was suggested that the two levels of plateau were based on the two zero current point in Ｉ-Ｖ curve under 2.5mmol/LK⁺ superfusion, whereas bursts were based on the Ｉ_Si, mainly I_Ca, for the low membrane level and I_f (and slow inactivated I_Na) for the high one.

Key words: purkinje fibers, action potential, early afterdepolarization, low K⁺, nifedipine, lidocaine, I_Ca, I_f