The effects of moderate intensity exercise training on the incidence of supraventricular arrhythmias and atrial connexin40 and connexin43 expression in young and aged rats (881.3)

Supraventricular arrhythmias are the most prevalent of all arrhythmias, with the elderly being at the greatest risk. Exercise training has been repeatedly shown to reduce supraventricular arrhythmic susceptibility. Connexin 40 (Cx40) is known to be the primary regulator of conduction between atrial cardiomyocytes and alteration of its expression has been associated with atrial arrhythmia development. Recent evidence also suggests that Connexin 43 (Cx43) assists in controlling atrial electrical conduction. We hypothesized that exercise training would reduce atrial arrhythmic susceptibility in young and aged animals and would be accompanied by changes in atrial Cx40 and Cx43 expression and/or phosphorylation. Groups of young and aged F344 rats underwent treadmill exercise training or sedentary handling. Subcutaneous electrocardiographic leads were then implanted following the respective exercise or sedentary protocols. The arrhythmic index (AI) was calculated using a modified scoring system totaling supraventricular arrhythmias during a baseline period (BL), sympathoexcitation (isoproterenol, 150 mg/kg s.c), and psychological stressor (BR). AI was significantly reduced during BL and ISO periods in young exercise animals compared to sedentary counterparts. Western blot analysis showed significantly greater atrial Cx43 expression in aged exercise compared to aged sedentary rats, while there was no significant change in the young animals. Preliminary evidence suggests an opposite pattern observed in atrial Cx40 expression, trending towards increased expression in young exercise compared to young sedentary rats, while showing no changes in aged animals. These preliminary results indicate moderate exercise training may be cardioprotective in a young animal model by reducing supraventricular arrhythmias and increasing atrial Cx40 expression while a similar aged model increases atrial Cx43 expression.