Procedure for use of Neurolab program
Cell and Mol Biol lab
1. Click on “My Computer” in the upper left portion of your
desktop. Then click on “C Drive” and then click on “Nia.htm.”
2. NeuroLab program opens; click on “About…”and look through
how accurate the program is, etc. You do not have to look at
“Setup,” “Orientation” or “For Instructors.” When done, go back
to the home page.
3. Click on “Start NeuroLab”
4. On the left side of your screen (sidebar), click on “Resting
Potential” (don’t go into the first lesson but the second)
5. Read the text in the main window. Click and read the link
“Nernst Equation” but do not click on “Ena - or EK variations” or
“the Membrane tutorial.”
6. After reading about the Nernst equation, click on “Start the
Simulation”; then click on OPEN in the next window.
7. You will see small windows on the left. Look at the “Patch
Parameters” window.
a. the sodium (Na) and potassium (K) channel density is
noted; this tells you how many channels are present. The more
channels, the faster the membrane potential (Em) changes. Don’t
change them now.
b. Leakage- a few ions can cross the membrane- or leak
across. Ignore this.
c. Intracellular Na and K concentrations: record the
starting values here (we will change them; to return the starting
value, click on the red checkmark that appears after changes are
made).
d. Ignore Ena, Ek, Eleak.
NOTE: SINGLE CLICK ONLY
8. Under the “Panel and Graph Manager,” click on “Na, K and
leak.” A new window appears.
9. Then click on “Run Control” on the “Reset and Run” panel. A
new THICK red line appears; this is the Em (membrane potential).
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It settles on a “stable” value that you can estimate with the Nernst
equation. Move the mouse to the thick red line (ignore the thin
horizontal red line) and left click; you will see the Em value in the
blue bar at the top (it is the y value). WRITE DOWN THIS
VALUE HERE:__________ mV (remember to note + or -).
Note your estimate of the Em with the Nernst equation: write down
equation with symbols, then plug in proper concentrations to
estimate the Em, finally, show your estimate (answer in correct
units; R= 1.987 cal/deg mole; Z is charge of the ion, F = 23,062
cal/volt equiv; T =temp in Kelvin (37C +273), Ln is natural log
base e= 2.718):
10. Now, change the K concentration outside the cell. If your
kidneys fail, K in the blood stream (extracellular K) will shoot up
to 80 mM. Change the extracellular K value to this number (from
5 mM) and then hit “Reset and Run” in the “Run Control” Panel.
Note that the Em depolarizes to a value of ________ mV.
This depolarization causes the heart muscle cells to contract
wildly- the heart begins “ventricular fibrillation (rapid heart beat)
that can cause death. It is called hyperkalemia.
Estimate this new membrane potential with the Nernst equation
below:
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11. Next, change extracellular K (and then “reset and run”) to the
following values and record the Em:
50 mM
0.5 mM
250 mM
Using Sigmaplot, graph out these four points: put Em (switch to
Volts from mV) on the Y axis, and extracellular K on the X axis.
Change the axis (which?) to natural log and see if you get a
straight line. Print the graph and put it in your lab notebook.
Rearrange the Nernst equation to see what the slope (m)
represents. The equation of a straight line of course is y = mx + b
(m is slope, b is y intercept). So the Nernst equation can be
changed to:
Em = Y = (RT/ZF) (ln [K]extracellular or X) - ln [K]inside
M is the slope and equal to the symbols…..
What is the numerical value of m (plug in for symbols)?
Is this the slope you noted in your graph (determine the slope in
the semi-log graph as slope is change in Y over the change in
X…)?
12. Next change the extracellular Na from140 to 10 mM, and then
to 200 mM. Each time, hit Reset and Run to produce the result.
Is there any effect on the red line? YES
NO (circle one).
Explain your answer.
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13. Reset all concentration values by clicking on the red arrows.
Now we will mimic an action potential in a nerve cell.
Remember that during an action potential, sodium channels rapidly
open up. So, the membrane changes since now Na is the most
permeable ion (use its concentrations to calculate the membrane
potential Em).
Click on “Na Conductance Only” in the upper left window. Note
that the Em goes from about _______ mV to _______ mV. Use
the cross hairs to find actual values (left click on the red line, see
the Y value in the blue bar above).
In a normal action potential, the Na channels then rapidly close and
the cell returns to the resting state where K channels are more open
than any other ion.
Using the Nernst equation, estimate the membrane potential when
Na channels are open- then compare this value to the value you
noted above. Be exact.
14. Now vary the extracellular Na; from 140 to 50 mM. Hit “reset
and run” and record the stable Em here: __________ mV. SO
NOW CHANGING THE SODIUM CONCENTRATION DOES
HAVE AN EFFECT ON THE Em because sodium is more
permeable than other ions.
15. Hit “quit” in the P and G manager to end the program.
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