[Effect of calpain 1 on structural remodeling and contractile dysfunction in atrial fibrillation: experiment with dogs].

Objective: To test the causal relationship between calpain activation and atrial structural changes during atrial fibrillation (AF).

Methods: The tip of a spiral mono-polar pacing lead was fixed to the right atrial appendages of 15 dogs randomly divided into 3 equal groups: calpain inhibitor group, undergoing continuous pacing with the impulse of 600 beats/min for 3 weeks and intravenous injection of N-acetyl-Leu-Leu-Met (ALLM), a calpain inhibitor for 3 weeks; control group, undergoing continuous pacing and intravenous injection of dimethyl sulfoxide (DMSO; and sham operation group, given DMSO injection without pacing. Ultrasonography was used to observe the changes of the structures of left atrium and left atrial appendage and the heart function as well. Specimens of atrial muscles were obtained. Calpain 1 activity was detected by Suc-Leu-Leu-Val-Tyr-7-amino-4-methyl-coumarin method. HE staining was conducted to observe the myolysis. Western blotting was used to detect the protein expression of troponin I (TnI) and myosin.

Results: The left atrial ejection fraction (LAEF) of the ALLM group was (41 +/- 6)%, significantly higher than that of the control group [(34 +/- 9)%, P < 0.05]. The left atrial appendage ejection fraction (LAAEF) of the ALLM group was (41 +/- 6)%, significantly higher than that of the control group [(35 +/- 6)%, P < 0.05]. Myolysis was extensive in the control group [(71.5 +/- 10.2)%], relatively rare in the ALLM group [(12.3 +/- 16.5)%], and was not seen in the sham operation group, with significantly differences among the 3 groups (all P < 0.01). The calpain 1 activity was positively correlated with the degree of myolysis (r(s) = 0.90 961, P < 0.01). The TnI level of the control group was (43 +/- 12)% that of the sham operation group (P = 0.001), the TnI level of the ALLM group was (51 +/- 11)% that of the sham operation group (P = 0.002) and was significant higher than that of the control group (P = 0.01). The level of myosin of the control group was (51 +/- 11)% that of the sham operation group (P = 0.002), and that of the ALLM group was (149 +/- 33)% that of the control group (P = 0.005).

Conclusion: Activation of and upregulation of expression of calpain participate in the structural remodeling of left atrial cardiac muscle and contractile dysfunction. Calpain inhibitor suppresses the increased calpain activity and reverses the structural remodeling of sustained atrial fibrillation. Calpain inhibition may therefore provide a possibility for therapeutic intervention in AF.