Mitochondrial Channels

Eukaryotic cells are living organisms surrounded by a surface membrane, which also house other membranes that define intracellular organelles. Membranes are lipidic structures impermeable to hydrophilic molecules (polar or charged); this is why they harbour proteins, called ion channels and carriers, catalysing the life-requiring exchange of material between a cell and the external space, and between organelles and the cytoplasm. At variance from carriers, ion channels form aqueous pores crossing the lipid bilayer that allow the highly selective transmembrane passage of charged species, namely inorganic ions (e.g. Na+, K+, Ca2+, Cl-), with high potency (105-108 ions per second are transported by a single molecule); they also possess regulatory domains that open and close the pore upon specific stimuli (electric or chemical). Mitochondria are organelles composed of two membranes, in either of which channels are present. However, while channels in the outer membrane (OM) are justified by its the overall high permeability, the finding of these entities in the inner membrane (IM) was unexpected in view of its implication in the process of oxidative phosphorylation that imposes an extremely controlled permeability to ions. After the initial phenomenological description, substantial advances in the functional - if not molecular - identification of several mitochondrial channels, disclose the possibility that they take part in crucial schemes of mitochondrial functionality, as well as in dramatic cell events.