Such a similarity does not mean that the velocities of the electrical and mechanical propagations are identical. Indeed, in addition to the conduction velocity, the excitation-contraction coupling as well as the rate ofcross-bridge cycling could also vary from one region to another along the heart tube . Nevertheless, our results indicate clearly that it is exclusively at the level of the atrioventricular canal that the mechanical propagation is slowed down during anoxia and abruptly blocked upon reoxygenation.It should be noticed that regions of the primary myocardium, such as the atrioventricular junction, appear to persist in and share functional (eg, slow conduction), morphological (eg, scanty myofibrils) and gene expression (eg, connexin) similarities with sinoatrial and atrioventricular nodes in the adult heart . In this context, the possibility that the pattern of response of the embryonic myocardium to PO2 changes observed in this work resembles that of the adult nodal system has to be taken into consideration and deserves further investigation. Buy quality medications online: find buy cheap alegra every time you need treatment.

CONCLUSION
This work characterizes for the first time the pathophysiology associated with strictly controlled deprivation and readmission of oxygen during early cardiogenesis. The remarkable dependence of the mechanical activity of the embryonic heart on oxygen availability appears to provide an interesting example of the tight interrelationship between oxygen utilization and early development of the cardiovascular system. Furthermore, our findings show that the preparation constitutes a promising in vitro model of heart for studying the cellular mechanisms underlying the disturbances induced by hypoxia and reoxygenation during embryonic or fetal life.