SFOS 11

Non-gated leakage channels (Na, K)

• Ventricular, Atrial
• Nodal

Phase 4 - iK1 (voltage-gated K channels) are open

Phase 0 - Fast Na channels open due to depolarization, Na rushes in

Phase 1 - Brief repolarization due to closing of Na channels, Ito1 (voltage-gated K channel) opens briefly

• Phase 2 - Plateau
• iK1 plugged with Mg++
• iCa (voltage-gated Ca channel) opens slowly, Ca enters cell

• Phase 3 - Repolarization
• iCa closes
• K channels open

• Phase 0 - depolarized by pacemaker potential
• iCa slowly opens, Ca enters cell, closes at peak

Phase 1 - not present

Phase 2 - not present

• Phase 3 - Repolarization
• iK opens

• Phase 4 - Pacemaker potential
• K channels close at max repolarization
• Resulting depolarization opens iCaT (Ca enters cell, depolarizes it)
• iF (Na channel) opens, depolarizes cell
• These currents bring to threshold

• Parasympathetic - uses Acetylcholine
• Decreases Na permeability in Nodal phase 4
• Decreases Ca permeability in Nodal phase 0
• Increases K permeability
• Slows the heart rate

• Uses Norepinephrine
• Increases Na, Ca permeability
• Decreases K permeability
• Increases heart rate

Mean cardiac vector