113 Normal Cardiac Electrical Activity Flashcards
Nerst Equation
The Goldman-Hodgkin-Katz Equation
Cardiac Action Potential summary
Cardiac Action Potential: Phase 4
PHASE 4: IK1 (the inward rectifier K current) and a small, background Na current (not shown in the figure)
Cardiac Action Potential: Phase 0
- Upstroke of the action potential
- INa , fast channel
- ICa (L-type), slow channel
Activation/opening of rapid Na and slow Ca channels in Phase 0ish
Cardiac Action Potential: Phase 1
Cardiac Action Potential: Phase 2
Phase 2 mainly due to (1) Slow inactivation of ICa allows Em to remain positive; (2) K conductances can’t make Em negative early in plateau because IK activates slowly; and (3) IK-1 is inwardly rectifying
Cardiac Action Potential: Phase 3
Main repolarizing K Currents:
- •Repolarization mainly due to IK, the delayed rectifier K+ current which has 3 components…
- –IKs Slow component
- –IKr Rapid component: blocked by antiarrhythmic agents
- –IKur Ultra-rapid component (mainly in atria)
- • and by the inward rectifier, IK1, which activates late in the plateau as the membrane potential decreases (resulting in less inward rectification
Phase 3: ICa inactivates; IK (IKr, IKs) activates in latter phase 2; as Em becomes more negative there is less inward rectification, allowing IK-1 to contribute
Inward Rectification
3 main K+ currents
- •Know about the 1st three (you’ll learn about others in the future)
- •Distinguished by different voltage, time, ligand dependencies and whether rectification is present. Examples are:
- –Inwardly rectifying K+ current, IK1: Responsible for the the resting membrane potential, repolarization.
- –Delayed rectifier repolarizing K+ currents, IK: IK-s, IK-r
- –Transient outward K+ current, Ito: Responsible (in part) for phase 1
