Slow-response cardiac action potential
Compared with fast-response, slow response action potential...
Difference in the phases
- Phase 0 much less steep
- Phase 1 absent
- Phase 2 short and not flat
- Phase 3 not very distinct from phase 2
In nodal tissues,
- Pacemaker potential present in phase 4
Difference in ion channels
- Voltage-gated sodium channel not involved
* No sharp spikes
* Not affected by tetrodotoxin
- In nodal tissues,
Very few iK1 type of K+ channel
--> Vm much less negative (-60mV) in phase 4
- Phase 2 is produced by Ca2+ current (L-type)
Difference in Vm
- RMP is about -60mV (compared to -90mV)
- Threshold potential = -40mV (rather than -65mV)
- Relative refractory period during the slow-response often extends well beyond phase 3
--> postrepolarisation refractoriness
- Recovery of full excitability is much slower than the fast response
Other notes
- Duration of AP = 150ms (compared to 250ms)
- Amplitude of AP = Smaller
- Conduction slow (0.05m/s)