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Regional expression of cardiac ion channels and cardiac electrical activity

Important differences in electrophysiological properties have been noted between different regions of the heart. Electrophysiological heterogeneity has also been detected within different parts of a given tissue, such as the ventricular subendocardium, midmyocardium and subepicardium. Although many molecular candidates for native ionic currents have been identified, the molecular basis of most currents is not completely understood. Heterogeneity of channel protein composition might well underlie the differences observed among the properties of ionic currents or the shape of the action potential in different regions of the heart. Techniques such as immunocytochemistry, immunohistochemistry and Western blotting have played an important role in identifying tissue expression of channel proteins as well as their cellular localization. This

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Modulation of Heart Function by Natural Neurotoxins

Cardiac muscle cells (myocytes) are electrically excitable cells, interconnected in groups that respond to stimuli as a unit, contracting together whenever a single cell is stimulated.

Unlike the cells of other muscles and nerves, these cells show a spontaneous, intrinsic rhythm generated by specialized “pacemaker” cells, located in the sinoatrial (SA), and atrioventricular (AV) nodes of the heart. The cardiac cells also have an unusually long action potential, which can be divided into five phases (0 to 4)1,2.

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