Changes in the action potential and transient outward potassium current in cardiomyocytes during acute cardiac rejection in rats

Abstract

Background: Acute cardiac rejection contributes to the changes in the electrophysiological properties of grafted hearts. However, the electrophysiological changes of cardiomyocytes during acute cardiac rejection are still unknown. An understanding of the electrophysiological mechanisms of cardiomyocytes could improve the diagnosis and treatment of acute cardiac rejection. So it is important to characterize the changes in the action potential (AP) and the transient outward potassium current (I_to ) in cardiomyocytes during acute cardiac rejection.

Methods: Heterotopic heart transplantation was performed in allogeneic [Brown Norway (BN)-to-Lewis] and isogeneic (BN-to-BN) rats. Twenty models were established in each group. Ten recipients were sacrificed at the 2nd day and the other ten recipients were sacrificed at the 4^th day after the operation in each group. Histopathological examinations of the grafted hearts were performed in half of the recipients in each group randomly. The other half of the grafted hearts were excised rapidly and enzymatically dissociated to obtain single cardiomyocytes. The AP and I_to current were recorded using the whole cell patch-clamp technique.

Results: Forty grafted hearts were successfully harvested and used in experiments. Histologic examination showed mild rejection at the 2^nd day and moderate rejection at the 4^th day in the allogeneic group after cardiac transplantation, while no evidence of histologic lesions of rejection were observed in the isogeneic group. Compared with the isogeneic group, the action potential duration (APD) of cardiomyocytes in the allogeneic group was significantly prolonged (APD₉₀ was 49.28±5.621 mV in the isogeneic group and 88.08±6.445 mV in the allogeneic group at the 2^nd day, P=0.0016; APD₉₀ was 59.34±5.183 mV in the isogeneic group and 104.0±9.523 mV in the allogeneic group at the 4^th day, P=0.0064). The current density of I_to was significantly decreased at the 4^th day after cardiac transplantation.

Conclusions: The APD of cardiomyocytes was significantly prolonged during acute cardiac rejection in rats, which might be partly attributed to decreased current densities of I_to .

Keywords: Acute cardiac rejection; action potential (AP); patch-clamp technique; transient outward potassium current.

Figure 1

Pathological examination of the grafted heart. (A,B) Showed that there is no evidence of acute cardiac rejection at the 2^nd day and the 4^th day in the isogeneic group (A, magnification, ×100; B, magnification, ×40). Inflammation with focal myocyte loss could be found in the allogeneic group at the 2^nd day after cardiac transplantation (C,D) (C, magnification, ×400; D, magnification, ×40). Inflammation with confluent foci of myocyte loss could be found in the allogeneic group at the 4^th day after cardiac transplantation (E,F) (E, magnification, ×40; F, magnification, ×400).

Figure 2

The morphology of AP of the cardiomyocytes. (A) The AP in rat cardiomyocytes of the isogeneic group at the 2^nd day after operation; (B) the AP in rat cardiomyocytes of the isogeneic group at the 4^th day after operation. AP, action potential.

Figure 3

Comparison of the APD, APA and RP of the cardiomyocytes between the two groups. (A) The APD₉₀ of cardiomyocytes was significantly prolonged in the allogeneic group at the 2^nd day (P=0.0016) and 4^th day (P=0.0064) after cardiac transplantation; (B,C) there was no significant difference in APA or RPs between the two groups. APD, action potential duration; APA, action potential amplitude; RP, resting potential.

Figure 4

I_to of the cardiomyocytes. (A) I_to in rat cardiomyocytes of the isogeneic group at the 2^nd day after operation; (B) I_to in rat cardiomyocytes of the allogeneic group at the 2^nd day after operation; (C) I_to in rat cardiomyocytes of the isogeneic group at the 4^th day after operation; (D) I_to in rat cardiomyocytes of the allogeneic group at the 4^th day after operation.

Figure 5

Comparison of the I_to of the cardiomyocytes between the two groups. I_to density in cardiomyocytes at the 2^nd day (A) and the 4^th day (B) after cardiac transplantation. The density of I_to in the allogeneic group was significantly decreased compared to the isogeneic group at the 4^th day (*, P<0.05; **, P<0.01).