Electric Cables of Living Cells. I. Energy Transfer along Coupling Membranes

The concept of "electric cables" involved in bioenergetic processes in a living cell was proposed half a century ago [Skulachev, V. P. (1971) Curr. Top. Bioenerg., Elsevier, pp. 127-190]. Membrane structures of a cell were considered as probable pathways for transferring transmembrane electrochemical potential. Further studies have shown that coupling membranes (inner mitochondrial membrane or bacterial cell membrane), i.e., those involved in the generation of membrane potential, can also serve for its transfer. A wide range of organisms from almost all major taxa have been discovered to employ the energy-transmitting function of coupling membranes. Macroscopic (millimeter or even centimeter in length) cable-like structures have been found, the most striking examples of which are giant mitochondria of some unicellular organisms (algae, fungi, protozoa) and animal tissues, filamentous mitochondria, mitochondrial reticulum in animal muscle tissue, and trichomes of cyanobacteria. The importance of such "electric cables" in cells or multicellular structures is determined by their ability to provide rapid energy exchange between metabolic counterparts, energy producers and energy consumers, as the diffusive transport of soluble macroergic molecules (ATP, etc.) requires much longer time. However, in the last 10-15 years, a new type of bacterial "electric cables" of presumably proteinaceous nature has been discovered, which serve a quite different purpose in cell bioenergetics. The molecular structure and functions of these cables will be discussed in the second part of the review ("Electric cables of living cells. II. Bacterial electron conductors").