LEVEL II

**Materials**

- Artificial lipid membrane from Exercise 6.6
- KCl electrodes 6
- DC voltage source
- Wheatstone bridge to monitor resistance 7

**Procedure**

- Insert a salt bridge connected to standard electrodes and
suitable for measuring both resistance and potential differences
across the membrane.
- Measure the resistance of the synthetic membrane by passing
a small DC current through the membrane and measuring the drop in
voltage.

If one knows the applied voltage (100-200 mV) and the measured voltage ( mV), the following formula will give the resistance (Ohm's law):R = (E / (E - E)) * R where R is the series resistance E is the calibrated input voltage E is the voltage appearing across the membrane. - Calculate the area of the membrane based on the diameter of
the drilled hole, and multiply R
(measured resistance) by the area of the membrane. This will give
a normalized resistance in ohms-cm.
- Compare your calculated value to the data in Table 6.4.
- Divide your calculated value by the thickness of the membrane 8 to yield the membrane resistivity or specific resistance.

Cell Biology Laboratory Manual

Dr. William H. Heidcamp, Biology Department, Gustavus Adolphus College,

St. Peter, MN 56082 -- cellab@gac.edu