Exercise 6.8 - Measurement of Transmembrane Potential
- Artificial membrane and recording apparatus from Exercise 6.6
- 1.0 M NaCl
- 1.0 M KCl
- Using the recording device from Exercise 6.7,
measure the voltage across the membrane with 0.1 M NaCl on both
sides of the membrane.
- Add 1.0 ml of 1 M NaCl to the external chamber and mix
gently. Immediately record the changes in voltage.
- When the change begins to stabilize, introduce 1.0 ml of KCl
into the teflon cup and continue to monitor the voltage.
- Graph the change in voltage across the membrane with time
and the addition of first NaCl and then KCl.
- Compare your results with the action potential of a typical
The same apparatus as that used for measurement of resistance can
be used to measure a potential, provided there is a difference in
the salt concentration in the teflon cup and outside of the cup.
This is best accomplished by the slight addition of a salt
solution to the teflon cup, although rather elaborate procedures
exist for complete substitution of the solutions (extreme care
must be taken not to rupture the membrane).
In vertebrate nerve, the potential that is generated is from an
influx of Na
followed by an efflux of K.
These fluxes are mimiced by the addition of NaCl to the outer
chamber, followed by an addition of KCl to the inner chamber.
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Cell Biology Laboratory Manual
Dr. William H. Heidcamp, Biology Department, Gustavus Adolphus College,
St. Peter, MN 56082 -- firstname.lastname@example.org