Multiple Facets of Maxi-K⁺ Channels : The Heme Connection

In the classic era of electrophysiology, two distinct classes of ion channels were thought to exist in cell membranes: one class accounted for the generation of action potentials and their propagation along nerve fibers (voltage-gated channels); the other class accounted for the electrical signals at the chemical synapses (transmitter-gated channels). The advances made for the last decades in terms of elucidating the structure and function of ion channels show how simplistic this view was. Several hundreds of ion channel types, encoded by dozens of gene families expressed in all tissues, are known to be gated by elaborate processes related not only to membrane voltage changes or transmitter release but also to membrane deformation, direct coupling to G proteins, or the presence of intracellular ligands such as Ca²⁺, H⁺, nucleotides, and lipids, among others. In addition, in most channels, gating and/or ion...