Cardiac Arrhythmias: Difference between revisions

Depending on cell type the resting membrane potential is between -50 to -95 mV, sinus node and AV nodal cells have a higher resting membrane potential (-50 to -60 mV and -60 to -70 respectively) in comparison with atrial and ventricular cardiomyocytes (-80 to -90 mV). The differences in resting membrane potential is mainly caused by differences in the the Na+ outside the cell and the K⁺ inside the cell. Sinus node cells and AV nodal cells (and to a lesser degree Purkinje fibers cells) have a special voltage dependent channel I_f, the funny current. Furthermore they lack I_K1, a K⁺ ion channel that maintains the resting membrane potential in atrial and ventricular tissue. This channel displays a slow depolarization in diastole, called the phase 4 diastolic depolarization, and results normal automaticity. Sinus node discharges are regulated by the autonomous nerve system and due to its high firing frequency dominates other potential pacemaker sites.