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Notes
      3. Old stuff
          3.2. Old physio stuff (around 2005)
              3.2.3. Physiology
                  3.2.3.2. Cardiovascular
                      3.2.3.2.2. Heart
                          3.2.3.2.2.2. Electrical activity
                              3.2.3.2.2.2.2. Fast-response cardiac action potential
 3.2.3.2.2.2.2.3. Potassium channels 

Potassium channels

 

Types of K+ current

  1. Inwardly rectifying (iK1)
  2. Transient outward (ito)
  3. Delayed rectifier (iK)

Inwardly rectifying K+ current (iK1)

  • Responsible for outward K+ current at RMP
  • Outward K+ current decreased when Vm positive
    * i.e. Phase 1 and 2
  • Outward K+ current increases as Vm become more negative in Phase 3
    --> Repolarisation accelerated

Transient outward K+ current (ito)

  • Starts in phase 1
  • Due to outward pressure of both electrical and concentration gradients
  • Help determine the duration of plateau

e.g.

  • In atrial myocytes, ito is more pronouced
    --> K+ current exceeds Ca2+ current early
    --> Plateau less pronouced in atrial cells

Delayed rectifier K+ current (iK)

  • Activated near the end of phase 0
  • Activation really slow (few hundred ms)
  • Very little contribution in phase 2
  • Significant contribution in phase 3

Two types: more rapid activation (iKr) and slower activation (iKs)
--> Distinction may contribute to difference in duration and AP shape between endocardium and epicardium
* [BL8:p19]

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