Voltage-Dependent Channels are Present in the Inner Membrane of Mitochondria

Abstract

The study of mitochondria with electrophysiological methods has been generally hampered by the small size of normal mitochondria and by the lack of suitable techniques applicable to such minute organelles. An attempt of this kind was nonetheless made by Tedeschi and coworkers (Tedeschi, 1980), who introduced microelectrodes into enlarged mitochondria, obtained from the liver of mice fed with the copper chelator agent oxalic acid (ciclohexylidenehydrazide), known as cuprizone. Contrary to some expectations (Ferguson and Sorgato, 1982, and references therein), a respiration dependent membrane potential was not detected with this technique (Campo et al., 1984). One possible reason for such result could be inherent to the impalement method itself, i.e. in the recognised difficulty of obtaining tight seals between the electrode and the membrane. Ions would then be free to permeate through the leak conductance and thus collapse the membrane potential. Recently, the patch-clamp technique has become available (Neher and Sakmann, 1976). This method is less invasive than the inpalement of microelectrodes and the relative ease of seal formation in the gigaohm resistance range makes the recording of low intensity currents feaseable (Hamill et al., 1981). With this in mind, we have tried to patch-clamp mitochondria deprived of the outer membrane. Our attempt was successful as we were able to record elementary currents through single channels from the inner membrane. It was found that these channels are voltage-dependent and slightly more permeable to chloride than to potassium ions. Interestingly, similar electrical properties were displayed by an as yet unidentified protein which coprecipitates with the membrane integrated part Fo, the membrane-associated and proton conductive part of the ATP syntase complex (Amzel and Pedersen, 1983) during the isolation procedure of the enzyme.