3. Physiology
        3.2. Cardiovascular
            3.2.2. Heart
                3.2.2.2. Electrical activity
3.2.2.2.2. Fast-response cardiac action potential

Fast-response cardiac action potential

[Ref: BL5:chp3]

Resting membrane potential

Resting membrane potential (RMP) of cardiac muscle
--> -90mV (on the inside)

Phases of fast-response cardiac action potential

Occurs in myocytes and conducting fibres

  1. Phase 0 - Rapid depolarisation
  2. Phase 1 - Early, brief partial repolarisation
  3. Phase 2 - Plateau
  4. Phase 3 - Repolarisation
  5. Phase 4 - RMP

Total duration: 250ms

Phase 0 - Rapid depolarisation

Transmembrane potential (Vm) reachs threshold potential

--> m gates in voltage-dependent sodium channels open

--> Inward rush of Na+

--> Rapid depolarisation to about +20mV on the interior

--> h gates start to close

Duration: 1-2ms

 

NB:

Phase 1 - Partial repolarisation

The interior of cell membrane becomes positive

--> Brief efflux of K+ (transient outward current, ito)

--> Brief, limited repolarisation

NB:

Phase 2 - Plateau

Ca2+ enter via Ca2+ channels (L-type)

--> Influx of positive charges (Ca2+) is balanced by efflux of positive charges (K+)

NB:

 

Phase 3 - Repolarisation

--> Vm becomes less positive

--> Further increases iK1 currents

--> Accelerates repolarisation

 

Phase 4 - RMP

Restoration of electrolytes

Other notes

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Created20050604
Reviewed20050815


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