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Electrical discharge from this cardiomyocyte may be characterized by a slow smooth transition from the Maximum Diastolic Potential (MDP, -70 mV) to the threshold (-40 mV) for the initiation of a new AP event. The voltage region encompassed by this transition is commonly known as pacemaker phase, or slow diastolic depolarization or phase 4.
Because the pacemaker potential represents the non-contracting time between heart beats , it is also called the diastolic depolarization. The amount of net inward current required to move the cell membrane potential during the pacemaker phase is extremely small, in the order of few pAs, but this net flux arises from time to time changing ...
(A brief chemical gradient driven efflux of Na+ through the connexon at peak depolarization causes the conduction of cell to cell depolarization, not potassium.) [27] These connections allow for the rapid conduction of the action potential throughout the heart and are responsible for allowing all of the cells in the atria to contract together ...
HCN4 is the main isoform expressed in the sinoatrial node, but low levels of HCN1 and HCN2 have also been reported.The current through HCN channels, called the pacemaker current (I f), plays a key role in the generation and modulation of cardiac rhythmicity, [13] as they are responsible for the spontaneous depolarization in pacemaker action potentials in the heart.
When, at the end of a sinoatrial action potential, the membrane repolarizes below the I f threshold (about −40/−50 mV), the funny current is activated and supplies inward current, which is responsible for starting the diastolic depolarization phase (DD); by this mechanism, the funny current controls the rate of spontaneous activity of ...
Since the 1940s, the concept of diastolic depolarization, or "pacemaker potential", has become established; this mechanism is a characteristic distinctive of cardiac tissue. [16] When the threshold is reached and the resulting action potential fires, a heartbeat results from the interactions; however, when this heartbeat occurs at an irregular ...
Early afterdepolarizations (EADs) occur with abnormal depolarization during phase 2 or phase 3, and are caused by an increase in the frequency of abortive action potentials before normal repolarization is completed. [1]
The agents from this heterogeneous group have an effect on the repolarization, they prolong the duration of the action potential and the refractory period. Also they slow down the spontaneous discharge frequency of automatic pacemakers by depressing the slope of diastolic depolarization. They shift the threshold towards zero or hyperpolarize ...