1. Choose tutorial "Chattering Ion Channels" , and Both Na+ and K+ channels

2. Record single channel currents with the preset values :

   • Tstop = 16 ms

   • testing level duration = 12 ms

   • testing level voltage at 0 mV

3. Press Reset & Run

   • the channels open stochastically

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

4. Compare the activity of these Na+ and K+ channels

   • each channel's open current is fairly constant ( square step )

     • Na+ = inward

     • K+ = outward

   • Na+ channels :

     • channels open and inactivate relatively quickly

     • Typically open briefly and earliest in the depolarizing step

     • They inactivate ( closures soon after they open ) , so you often see short bursts of inward current

     • At 0 mV , Na+ current is usually inward ( below the baseline )

   • K+ channels :

     • K+ channels open more slowly but do not inactivate in the same way

       • they can remain open or flicker open/closed for longer

     • Tend to open a bit later and often show longer open times ( though still flickering )

     • At 0 mV ( assuming EK ~ -80 mV ) , the K+ current will be outward

   • Because these are single-channel recordings , you see individual "square" steps of current for each channel opening

5. Repeat with testing voltages of +30 mV and then −30 mV

   • @ +30 mV :

     • Na+ = inward current , small amplitude

     • K+ = outward current , large because +30 mV is far away from -80 , potassium's equilibrium potential

   

   • @ -30 mV :

     • Na+ = inward current , larger

     • K+ = outward , smaller

   

6. Discuss the amplitude and time course of the currents , and which type opens first

   • Na+ :

     • opens very quickly after depolarization and then inactivates

   • K+ :

     • open with a delay , and then stay open for longer

    

7. Construct an IV plot for this channel activity ( +80 mV to −80 mV , 40 mV increments ) , and confirm the ion selectivity

    

8. Increase the number of sodium channels to 3 and K+ channels to 3 when stepping to +30 mV , 0 mV , and then −30 mV

   

   

   

9. Discuss what happens , including how many channels are open at peak current

   • you see discrete “steps” in the current trace

   • each step corresponds to the opening of one additional channel

   • If multiple channels open at the same time, you’ll see a larger amplitude

    

10. Increase the number of sodium channels to 10 and K+ channels to 10 when stepping to +30 mV , 0 mV , and then −30 mV

    

    

    

11. Discuss what happens , including how many channels are open at peak current

    • Stochastic Variability : The exact number of channels open at any given time is random, governed by each channel’s probability of opening.

    • Faster vs. Slower Activation : $N{a}^{+}$$Na^+$ vs. $K^{+}$$K^+$ gating kinetics remain the same; increasing channel count just increases the likelihood of multiple channels opening simultaneously.

    • Peak vs. Sustained Current : $N{a}^{+}$$Na^+$ provides a fast “spike” of inward current, while $K^{+}$$K^+$ provides a more delayed but sustained outward current.

Single-Channel Currents : $N{a}^{+}$$Na^+$ is inward at most voltages tested (except near +55 mV), while $K^{+}$$K^+$ is outward (except near −80 mV).

Voltage Dependence : Inward $N{a}^{+}$$Na^+$ currents get smaller as the test pulse approaches the $N{a}^{+}$$Na^+$ reversal potential; outward $K^{+}$$K^+$ currents get larger with more positive voltages.

Activation Kinetics : $N{a}^{+}$$Na^+$ activates (and inactivates) faster; $K^{+}$$K^+$ activates more slowly but can remain open longer.

Increasing Channel Number : Increases the probability and magnitude of multiple-channel openings, thus raising peak currents and showing stepwise increments in the current traces.