Severe and early alteration of action potential during acute cardiac rejection in rats

Introduction: Alteration of cardiac action potential and its adaptation to heart rate could contribute to cardiac dysfunction and arrhythmias during acute cardiac rejection. Methods and Results: Heterotopic heart transplantation was performed in allogeneic and syngeneic rats in which 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 frequency, 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% repolarization (82.5%, 75.6%, and 70.8%, respectively) and in action potential amplitude (+17.9 mV), and the resting potential was decreased (-5.3 mV), A lack of adaptation of action potential duration to the driving frequency was observed in the rejecting heart group in contrast to controls (n = 20) and nonrejecting hearts (n = 13), Similar results were observed 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 driving frequency is considerably altered during acute rejection, A humoral factor could contribute to cardiac dysfunction.