SEVERE AND EARLY ALTERATION OF ACTION-POTENTIAL DURING ACUTE CARDIAC REJECTION IN RATS

Introduction: Alteration of cardiac action potential and its adaptatio n to heart rate could contribute to cardiac dysfunction and arrhythmia s during acute cardiac rejection. Methods and Results: Heterotopic hea rt transplantation was performed in allogeneic and syngeneic rats in w hich the action potentials of right and left ventricles were measured at 1, 2.5, 3.3, and 5.7 Hz successively using standard microelectrode techniques and compared with nontransplanted hearts, For each frequenc y, we measured action potential amplitude, action potential duration, transmembrane resting potential, and Vmax, In the right ventricle, at 1 Hz in the presence of rejection (n = 40), a significant increase was observed in action potential duration at 20%, 50%, and 70% repolariza tion (82.5%, 75.6%, and 70.8%, respectively) and in action potential a mplitude (+17.9 mV), and the resting potential was decreased (-5.3 mV) , A lack of adaptation of action potential duration to the driving fre quency was observed in the rejecting heart group in contrast to contro ls (n = 20) and nonrejecting hearts (n = 13), Similar results were obs erved in the left ventricle and surprisingly in the native hearts (n = 11) of recipients with allografted rejecting hearts in the abdominal position. Conclusion: Action potential and its adaptation to the drivi ng frequency is considerably altered during acute rejection, A humoral factor could contribute to cardiac dysfunction.