ABSTRACT
Ion channels are classified on the basis of ion selectivity and gating. Selectivity refers to the capacity of some channels to distinguish between ions [e.g., sodium (Naþ), potassium (Kþ), calcium (Caþ2), or chloride (Cl-)], allowing only selective ions to pass through the pore. Gating refers to the course of transformation between open and closed states. The opening and closing of most channels is determined by biological signals, such as alterations in membrane potential (voltage-gated channels), binding of intracellular or extracellular ligands (ligand-gated channels), change in temperature, or mechanical stress.
