Abstract

Ion channels function to orchestrate an exquisite array of physiological processes, including nerve impulses, muscle contraction, regulation of cell volume, and cell signaling in all organisms. The electric current in a signaling event is generated by ion flux across the cell membrane that is controlled by the opening and closing of ion channels, including those permeable to potassium, sodium, calcium, and chloride ions. The direction of the ion fluxes is determined by the membrane potential and preset transmembrane ionic gradients, which are established and maintained by specific ion channels and the Na⁺/K⁺ ATPase. For certain signaling modes, such as the generation of the action potential, it is important that the ion channels involved are only permeable to specific ions and impermeable to others. Particularly important to signaling in nerve and muscle are potassium and sodium channels, which display a very high level of selectivity. Therefore, some ion channels have evolved to exhibit high ionic selectivity, which is fundamental to electrical signaling.