The movement of inorganic ions across biological membranes of animals plays a central role in the perception and integration of, and reaction to, environmental signals by the organism. Examples include vision, the integration and processing of this information (brain function), and the reaction of the organism to this information, for instance, muscle contraction (Fig. 1). Cells have the ability to hydrolyze adenosine triphosphate (ATP). The energy thus released is used to transport sodium and potassium ions across the cell membrane against a concentration gradient. This process establishes the transmembrane voltage (Vm) of the cell membrane. The transmembrane voltage is perturbed by the movement of inorganic ions (generally Na+, K+, Cl−, and Ca2+) along the concentration gradient and voltage difference across the cell membrane that occurs in signal transmission between cells. There are many different transmembrane channel-forming proteins, which are activated by (1) a concentration gradient of inorganic ions across the membrane, (2) the transmembrane voltage, (3) the binding of specific ligands to a channel-forming protein. (4) Some proteins use the energy liberated by the hydrolysis of ATP to transport inorganic ions against a concentration gradient. Only one example of each of these various proteins will be mentioned. In each case, the protein chosen is the one about which we have the most information. The proteins that facilitate inorganic ion transport across biological membranes are discussed in an order that illustrates their function in the life of an organism.
© 2018 Biocyclopedia | All rights reserved.