Cardiac Arrhythmias: Difference between revisions

Immediately following rapid depolarization, the inactivation of the Na⁺ channel (I_Na) and subsequent activation of the outward K⁺ channel (I_TO) and the Na⁺/Ca²⁺ exchanger produce a early rapid repolarization. Due to the absence of I_Na in the upstroke of sinus node and AV node cells and the subsequent slower depolarization, this rapid repolarisation is not visible in their action potentials.

The plateau phase represents an equal influx and efflux of ions producing a stable membrane potential. The influx is mediated by Ca²⁺ through the open L-type Ca²⁺ channels and the exchange of Na⁺ for internal Ca²⁺ by the Na⁺/Ca²⁺ exchanger. The efflux is the result of outward current carried by K⁺ and Cl^- ions.