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 resting membrane potential is mainly caused by differences in the the K⁺ outside the cell (5mM) and the K⁺ inside the cell (140mM). 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. The I_f channel causes a slow depolarization in diastole, called the phase 4 diastolic depolarization, which results in normal automaticity. Sinus node discharges are regulated by the autonomous nerve system and due to the high firing frequency the sinus node dominates other potential pacemaker sites.