A study was made of the effect of mitochondrial size on the electrical properties of the membrane and the internal conductivity of mitochondria. The dielectric constant and electrical conductivity of suspensions of guinea pig heart mitochondria were examined in the frequency range 5 x 105 to 2.5 x 108 C.P.S.

Membrane capacity was calculated to be 1.1 to 1.3 µf./cm.2 and was virtually the same in mitochondria whose surface area was made to vary by a factor of 4 by osmotic means. This finding suggested that some mechanism must exist for the transfer of mitochondrial material into membrane structure during fluctuations in mitochondrial size.

The electrical capacity of the membrane was unaffected by a 33-fold change in potassium chloride concentration.

The internal conductance of swollen mitochondria was 2 to 3 times lower than that of the external medium. In shrunken mitochondria the internal conductance was virtually independent of the conductivity of the external medium.

These results were discussed in relation to current concepts of mitochondrial structure.

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