Effects of different loading swimming exercises on structure of myocardial intercalated disk of ventriculus sinister and connexin 43 in rats

Objective: To explore the effects of different loading swimming exercise on structures of myocardial intercalated disk of ventriculus sinister and connexin 43(Cx43) in rats, so as to provide some information for the changes of physiology and pathology by the exercise-induced injury and recuperation of cardiac muscles. Method: SD rats were randomly divided into two groups: different loading exercise group and exhaustive exercise group. In the different loading exercise group, 12-week low, moderate and high loading swimming models were carried out in rats. In the exhaustive exercise group, a single exhaustive swimming was carried out in rats. After exercise, rat's ventriculus sinister were cut off, and treated with routine procedures of transmission electron microscopy before observing the structures of intercalated disks. Immunohistochemical technique and image-analysis method were used to study the changes in distribution and content of Cx43 in myocardial tissues. Result: In control group rats ventriculus sinister showed clear structure of myocardial intercalated disks, which were composed of adhering junction, desmosome and gap junction and arranged as a flight of stairs. Cx43 was mainly distributed in intercalated disk. In low and moderate loading swimming groups the structure of intercalated disk and the distribution and content of Cx43 were similar to that of control group. In high loading swimming group the gaps of intercalated disks became wider, the contents of Cx43 decreased, and distribution of Cx43 at side-to-side junction of myocardial cells increased. In exhaustive exercise group the myocardial intercalated disks were disorganized and some regions of intercalated disks were destroyed or folded; the content of Cx43 was similar to control group at the end of exhaustive exercise, but significantly decreased with time prolongation after exhaustive exercise. Conclusion: High loading swimming and exhaustive exercise could destroy the structures of myocardial intercalated disks of ventriculus sinister, and result in degradation and change in distribution pattern of Cx43.