Exercise for Cardiovascular Disease Prevention and Treatment From Molecular to Clinical, Part 1

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these studies are consistent with data from Soci and colleagues showing an increase

in the ratio α/βMHC during long term swimming training at low intensity [ 28 ].

Otherwise, myosin also has a second chain called myosin light chain (MLC). A

study using a treadmill training program showed an increase in the expression of

atrial myosin light chain 1 (aMLC-1) in the trained ventricular tissue of healthy rats

[ 29 ]. Same authors also suggested that the increase is greater in myocytes originat-

ing from the sub-endocardial region compared to the cardiomyocytes isolated from

the sub-epicardium [ 30 ].

1.2.2 Troponin

Troponin is a protein complex that plays a predominant role in the contraction of the

heart muscle and has three distinct subunits. The Troponin C which is responsible

for binding to calcium, the troponin I allowing the inhibition of actin binding myo-

sin and the troponin T binding to tropomyosin.

Despite the few studies on this protein, the effect of physical training on the level

of troponin expression appears to be divergent between rats and humans. A study

using swimming training protocol, in healthy rats, has suggested that exercise train-

ing induces an increase in the expression of cardiac troponin and this increase is

greater if the training protocol is carried out at high intensity [ 21 ]. By contrast, a

study in older men and women subjects, following 12 or 24 weeks of resistance

training, suggests no difference in cardiac troponin T and I expressions with values

of 6,4 and 4,1 ng/L before the protocol and 6,1 and 3,8 ng/L respectively for tropo-

nin T and I, after a 24 weeks training [ 31 ]. The observed differences between spe-

cies can be due either to the type of training or to the model of study used.

2 Calcium Homeostasis and Contractile Under Exercise

Training

2.1 Contractility and Intracellular Ca2+ Transients

The initial results related to the effects of exercise training on cardiomyocytes con-

tractile function also were non-consensual. Laughlin and colleagues [ 32 ] first stud-

ied the effects of endurance training on cardiomyocytes function. After 16 weeks of

progressive treadmill training, the shortening characteristics during a 0.2 Hz electri-

cal stimulation of ventricular myocytes of trained male rats did not differ from sed-

entary ones. Moore and colleagues [ 13 ] observed an exercise training induced

increase of shortening on rat cardiomyocytes stimulated at 0.07 Hz. Zhang and col-

leagues [ 33 ] demonstrated a decrease in maximal shortenings amplitude and veloc-

ity in ventricular myocytes of sprint trained-male rats during 8 weeks. Discrepancies

of the results could be explained by different experimental conditions, e.g. different

5 Structural, Contractile and Electrophysiological Adaptations of Cardiomyocytes...