Effect of Exercise Training on Myocardial L-type Calcium Channel of Obese Rats

Experimental studies have showed that obesity for 15 weeks promotes myocardial dysfunction associated with changes in the L-type Ca2+ channel activity. Authors have proposed that exercise training (ET) increases the sensibility to Ca2+ and improves the function of proteins involved in myocardial Ca2+ handling, including the L-type Ca2+ channels. PURPOSE: To evaluate the effect of exercise training on myocardial L-type Ca2+ channel of obese rats induced by unsaturated high-fat diet. METHODS: Male 30-day-old Wistar rats were fed standard (C, n=40) and alternately four palatable unsaturated high-fat diets (Ob, n=40) for 20 weeks. After induction processes (5 weeks) and exposure to obesity (15 weeks), rats were redistributed into two groups regarding the presence or absence of exercise training: control (C; n=12), control submitted to exercise training (ET; n=14), obese (Ob; n=10) and obese submitted to exercise training (ObET; n=11). ET and ObET performed 12 weeks of moderate-intensity exercise training (55-70% of the maximum running speed) on a treadmill once per day, five days per week. The nutritional profile was assessed by analysis of body weight, body fat and adiposity index. Myocardial function was assessed by isolated papillary muscle evaluation at baseline and after inotropic and lusitropic maneuvers, such as post-rest contraction and increases in extracellular Ca2+ concentration. The evaluation of L-Type Ca2+ channel activity was performed using Diltiazem hydrochloride (10-4 M), in the presence of cumulative Ca2+concentration. RESULTS: ET decreased the body weight (Ob: 622 ± 48 vs. ObET: 553 ± 47 g; p <0.05), body fat (Ob: 57 ± 3 vs. ObET: 29 ± 3 g; p <0.05) and adiposity index (Ob: 9.2 ± 0.5 vs. ObET: 5.3 ± 0.5 g; p <0.05) in relation to Ob rats. Papillary muscles showed similar behavior between the groups at baseline and after inotropic maneuvers. The maximal inhibition of developed tension in response to diltiazem was 85 ± 7%, 86 ± 5%, 85 ± 6% and 88 ± 5% at Ca2+ exposure of 0.5 mM in C, Ob, ET and ObET rats, respectively, but without significant effects between the groups. At the same time, diltiazem displayed similar negative inotropic behavior on +dT/dt and -dT/dt without significant changes. CONCLUSION: Exercise training does not promote alterations on myocardial L-type Ca2+ channel activity in obese rats.