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

    image-20250127101446270

    • @ -30 mV :

      • Na+ = inward current , larger

      • K+ = outward , smaller

    image-20250127101528654

  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

    image-20250127101645261

    image-20250127102103270

    image-20250127101742194

  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

    image-20250127101854649

    image-20250127101948052

    image-20250127102032667

  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 : Na+ vs. K+ gating kinetics remain the same; increasing channel count just increases the likelihood of multiple channels opening simultaneously.

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


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

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

Activation Kinetics : Na+ activates (and inactivates) faster; 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.