What happens to AP when K+ currents are reduced and how might the cardiac AP waveform be corrected ?

1. Choose tutorial "The Ca Action Potential"

2. Click IClamp ( in Stimulus Control window )

3. Click Cardiac-like AP

4. Move "Reset ( mV ) to -80 mV

5. Move total # ( ms ) to 35 ms

6. Click Reset & Run ( in Run Control window )

7. Right Click graph , hold , view , view=plot

1. Describe the AP waveform and currents that you see

   

   • transient , long lasting

Impact of a less negative E_K AP waveform

8. Reduce $E_K$$E_K$ to $-70mV$$-70\ mV$ , reset and run

2. What happens to the AP waveform and why ?

   

   • shifted left , occurs sooner

   • didn't start in as deep of a well

9. Reduce $E_K$$E_K$ to $-76mV$$-76\ mV$ , reset and run

3. What happens to AP waveform ?

   

   • in the middle now

4. Determine two ways of altering parameters to counteract the impact of the less negative $E_K$$E_K$ on the AP waveform ( of course , without altering $E_K$$E_K$ )

   • increase potassium conductance

   • decrease sodium or calcium conductance

Reduced $K_v$$K_v$ Activity

10. Reset back to “normal” cardiac-like AP

11. Reduce $K_v$$K_v$ density to $0.035$$0.035$

5. What happens to AP waveform ?

   

   • repolarization phase never stops

   • less voltage gated potassium channels ➡️ less outward potassium current ➡️ repolarization takes forever

6. Determine two ways to correct back to near “normal” cardiac-like waveform and why these changes work ( without increasing $K_v$$K_v$ density )

   • increase potassium leak conductance

     • helps repolarize

   • decrease calcium conductance

     • decreases depolarization time