Electrophysiology of the Cardiac Cell:
There are many different kinds of cardiac muscle cells (sinus nodal, Purkinje fiber, ventricular, atrial, atrio-ventricular nodal) in terms of: resting membrane potential, action potential magnitude, action potential duration, maximum rate of rise of action potential, propagation velocity, and fiber diameter. Some cells are of the pacemaker type, showing constant automaticity, while others are follower cells or reserve pacemaker cells (Table 1).
K+ concentration is high inside the cell, while Na+ and Ca++ are low. Na+ concentration is much higher outside the cell, while K+ is low. These ion distributions are maintained by specific ion pumps, some directly utilizing ATP, others involving exchange processes (Figure 3).
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