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Nevertheless results related to the increase of cardiomyocytes length is contro-versial as these authors observed no differences in cardiomyocytes length whatever
was the regional origin (endo- or epicardium) or sedentary or trained rats [ 8 ].
In this paper and others [ 7 , 14 , 15 ] the main observed effect of training is focusedon the width (and by implication on depth) of cardiomyocytes with a greatest hyper-
trophy effect in endocardium wall region [ 8 ]. To further complicate the situation,
other data [ 6 ] indicated a slight reduction of the cardiomyocytes width (−2%) under
training.
1.1.4 Effects Dependence on Training Intensity
Clinical and epidemiological studies suggest that beneficial effects of regular
exercise depends on intensity or amount of work performed (see for example
[ 16 ]). So the group of Wisloff [ 15 ] have compared the effects of moderate versus
high intensity exercise on different parameters in rats running on treadmill. In
these experiments only high intensity type of chronic exercise was able to
increase (4%) the left ventricle weight. Regarding the cardiomyocytes length the
two types of intensity of training was able to enlarge the cells length but with a
prominent effect obtained with the high intensity type (14%) compared to the
moderate intensity training (5%). The same trend was observed for the cardio-
myocytes width (as well as by implication for volume). By contrast, Wang and
colleagues [ 17 ] also reported effects of both moderate and high intensity train-
ings on length and width of cardiomyocytes but without significant differences
between the two modes.
1.1.5 T-Tubules: A Minimal Change
One another morphologic parameter that could be addressed was the degree of
development and shape of T-Tubules network. Transverse tubules, which are invagi-
nations of the plasma membrane in close relation with the sarcoplasmic reticulum
membrane, allows the membrane depolarization and calcium entry uniformly across
to the whole cell and initiate coordinate contraction of the cardiomyocyte (see [ 18 ]).
Alteration or changes of these structures involved in such an important mechanism
would have certainly drastic impact on the physiological function of these cells.
Kemi and colleagues [ 14 ] studied, through Di-8-ANEPPS labelling, two param-eters related to T-tubules membrane system: T-tubules density and T-tubules spac-
ing. Except a slight increase of the T-tubules density at the center (x-axis) of
cardiomyocytes, no difference in T-tubules density or spacing could be detected
between sedentary and trained animals.
5 Structural, Contractile and Electrophysiological Adaptations of Cardiomyocytes...