1. Choose tutorial "Chattering Ion Channels"

2. Click "Both Na and K Channels ( default )"

3. Record single channel currents with the preset values

4. Set Tstop at 16 ms and

5. Set testing level duration at 12 ms

6. Reset & Run

Hint: You will need to repeat Reset & Run many times to get a good feel for things.

1. Does the channel activity look like the macroscopic currents from previous tutorials?

   • Previous Tutorial ( 4 ) : https://youtu.be/09Yiog8yrgs

   • Current Tutorial ( 8 ) : https://youtu.be/CTE4hZGLvOY

   • No , the sodium channels are opening much later in time

   Previous Tutorial

   Current Tutorial

7. Open the extended time axis.

8. Record the longest open time period and longest closed time period for each channel type at each testing level voltage

   • ( +80 mV to −80mV , 40 mV increments ) , repeating 5 times.

• Longest Closed Time = largest space between square waves

• Longest Open Time = largest square wave itself

2. Describe how these measures of channel activity ( median value ) vary with voltage.

   • sodium are voltage sensitive , they spend more time open with more positive voltage clamps

     • so they activate rapidly , and then inactivate

   • potassium channels are open for almost infinite amount of time at more positive voltage clamps

9. Close the extended time axis.

10. Select Na+ Channel Only

11. Change the test voltage to 20 mV and then to −30 mV

3. Measure the time required before the first channel opens for multiple trials

   • @ $+20mV$$+20\ mV$ = 1.1 ms

   • @ $-30mV$$-30\ mV$ = 2.5 ms

12. Make sure Testing Voltage is at −30 mV

13. Increase Na+ channel number to 100.

14. Shorten the pulse duration progressively toward 1 ms

4. Indicate when the largest single channel current occurs during the pulse protocol

   • setting the voltage clamp's testing level duration to 8 milli seconds seems to produce the largest single channel current duration

15. Select K+ Channel Only

16. Increase K+ channel number to 10

17. Step to 0 mV as well as to −50 mV.

18. Set EK to −30 mV and step to 0 mV.

5. Indicate what happens to the current at the end of the pulse , and what might cause it to occur.

   • @ $0mV$$0\ mV$ :

     • it trails off at the end , similar to normal re-polarization phase

   

   • @ $-50mV$$-50\ mV$ :

     • smaller current

     • discrete square wave bursts

     • its too hyperpolarized for potassium to really fire

     

   • with $E_K=-30mV$$E_K = -30\ mV$ and @ $0mV$$0\ mV$ :

     • you can see current reversal at 4 ms

     • there is initially outward current because :

       • $V_m>E_K$$V_m > E_K$

     • but later , after 4ms , there is inward current because :

       • potassium channels were allowed to open due to voltage clamp

       • $V_m\approx E_K$$V_m \approx E_K$

       • when enough potassium has exited the cell , the gradient flips , and now their is inward current

     • also you then see repolarization phase , trending towards zero current

   

19. Select Both Na+ and K+ channels

6. Record the responses of 100 K+ and Na+ channels at various voltages.

   

20. Increase channel number to 1000 and then 10,000