3/20/2023 0 Comments Pspice ipulse![]() Although pathologies of this specialized conduction system are common in humans, especially among the elderly, their molecular bases have not been defined. Differences in the connexin phenotypes of specific regions of the human heart and experimental animal hearts must be considered in future experimental or modeling studies of cardiac conduction.Īctivation of cardiac muscle is mediated by the His-Purkinje system, a discrete pathway containing fast-conducting cells (Purkinje fibers) which coordinate the spread of excitation from the atrioventricular node (AV node) to ventricular myocardium. These differences likely play a role in regulating cardiac conduction velocity. The relative amounts of individual connexins and the number and size of gap junctions vary greatly in specific regions of the human heart with different conduction properties. Minimal Cx37 and Cx46 immunoreactivity was detected between occasional atrial or ventricular myocytes. Gap junctions in ventricular myocardium contained mainly Cx43 and Cx45 only a very small and amount of ventricular Cx40 was detected in subendocardial myocyte junctions and endothelial cells of small to medium sized intramural coronary arteries. ![]() Junctions in the bundle branches were the largest in size and contained abundant amounts of Cx40, Cx43, and Cx45. Atrial gap junctions were larger than nodal junctions and contained moderate amounts of Cx40, Cx43, and Cx45. AV node gap junctions were also small and contained mainly Cx45 and Cx40 but, unlike the sinus node, also expressed Cx43. Sinus node gap junctions were small and sparse and contained Cx45 and apparently smaller amounts of Cx40 but no Cx43. ![]() Patterns of expression of these connexins in the human heart differed from those in previous animal studies. AV node and His bundle, the bundle branches, and the left and right ventricular walls. The distribution and relative abundance of Cx37, Cx40, Cx43, Cx45, and Cx46 were studied immunohistochemically using monospecific antibodies and frozen sections of the sinoatrial node and adjacent atria. To elucidate determinants of conduction properties in the human heart, we characterized connexin phenotypes of specific human cardiac tissues with different conduction properties. However, there is significant interspecies variation in the types and amounts of gap junction subunit proteins (connexins) expressed in disparate regions of mammalian hearts. Alterations in gap junctions may contribute to development of arrhythmia substrates in patients. Gap junction channels are major determinants of intercellular resistance to current flow between cardiac myocytes. Based on this view, we think that most of the paradox about the role of gap junctions in cardiac impulse propagation will be solved Then opening the gap junction produces AP. Closure of gap junctions allows the negative cleft potential to develop and enhance the cell excitability by reducing cell potential. It seems that gap junction has a dynamic behavior in each cardiac cycle, managing different routes of propagation in the diverse moments of normal cycle. These results offer a new view on action potential propagation in which both of the abovementioned mechanisms are necessary for normal cardiac functioning, but in different times of a cardiac cycle. Our results demonstrate that although the mechanism of electrical field alters the resting potential of the post-junctional cell, but it is not sufficient to excite the post-junctional cell. ![]() ![]() We simulated the mechanism of electrical field and local circuit current separately, studied the effect of these mechanisms on action potential propagation and compared them with each other. It is demonstrated that in the lack of gap junctions, electrical field is sufficient for action potential propagation. Electrical field has been suggested as the main effective mechanism in action potential propagation. It seems that some other mechanisms are involved in the action potential propagation. Some researches offered that myocardial cells may not require low-resistance connections for successful propagation of action potential. In the last few years, some different evidences suggest another view on action potential propagation via myocardial cells. For many years, local circuit current through gap junctions has been seemed to be the main fundamental route for impulse transmission. ![]()
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