Exercise 6.7 - Electrical Properties of Artificial Membranes

LEVEL II

Materials

Procedure

  1. Insert a salt bridge connected to standard electrodes and suitable for measuring both resistance and potential differences across the membrane.

  2. 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_m = (E_m / (E_i - E_m)) * R_i
    where R_i is the series resistance

    E_i is the calibrated input voltage

    E_m is the voltage appearing across the membrane.

  3. Calculate the area of the membrane based on the diameter of the drilled hole, and multiply R_m (measured resistance) by the area of the membrane. This will give a normalized resistance in ohms-cm^2.

  4. Compare your calculated value to the data in Table 6.4.

  5. Divide your calculated value by the thickness of the membrane 8 to yield the membrane resistivity or specific resistance.

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Cell Biology Laboratory Manual
Dr. William H. Heidcamp, Biology Department, Gustavus Adolphus College,
St. Peter, MN 56082 -- cellab@gac.edu