Electrical properties of giant mitochondria studied with a double impalement technique

Abstract

THE electrical properties of the membrane of giant mitochondria (4–10 μm in diameter) can be studied directly with micro-electrodes. Tupper and Tedeschi^1–4 have studied mitochondria isolated from Drosophila (approximately 4 μm in diameter), and found a positive potential in the range of 5–15 mV and a specific resistance in the range of 1–4 Ω cm² (assuming no invaginations of the mitochondrial membrane). The potentials were not found to depend on metabolic state². The microelectrodes were judged to be in the internal mitochondrial space from the fact that the potentials were osmotically sensitive (decreasing with osmotic swelling in a predictable manner). The positive potentials correlated with the distribution of carboxylic anions, which partition with a higher concentration inside the mitochondria. Furthermore, the potentials were collapsed by the addition of acetate^3,4, but not chloride⁴ to the external medium. Presumably acetate enters and depolarises the potential. These observations further support the idea that the electrodes are in the inner mitochondrial space.