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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
 3.2.3.2.2.2.2.1. Voltage-dependent sodium channel 
 1. Refractory period

Voltage-dependent sodium channel

[Ref: BL5:chp3]

aka "Fast sodium channel"

@@ structure

 

Blocked by tetrodotoxin

2 gates

Both voltage dependent

m gates (activation gates)

  • Triggered when Vm reach about -65mV
  • Rapid opening (within 0.1-0.2ms)
  • Responsible for rapid sodium influx
    * i.e. Phase 0

h gates (inactivation gate)

  • Tends to close as Vm becomes less negative
  • Inactivation is exponential.
  • Initially Na+ influx slows down quickly, then more gradually.
  • Complete closure take >100ms
  • Stay closed until the cell has partially repolarised during phase 3

 

 

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