Acid-sensing ion channels (ASICs) are Na+ channels activated by external protons. ASIC4 is a member of the ASIC family that includes another three members: ASIC1, ASIC2 and ASIC3. The ASIC family is in fact part of a large channel superfamily known as degenerin/epithelial Na+ channels (DEG/ENaC) and share the same basic characteristics: two transmembrane spanning domains, a large extracellular domain and short intracellular N and C termini.nThe functional ASIC channel is composed of 4 subunits, which can form either a homo or heterotetramer. The subunit composition of the tetrameric channel will determine its biophysical properties such as pH sensitivity, inactivation kinetics and channel pharmacology. In fact, the ASIC4 protein does not appear to function as a proton-gated channel when expressed alone in heterologous systems and therefore a modulatory role for this subunit has been proposed.Expression of the ASIC4 protein has been detected in brain, pituitary gland, spinal cord and inner ear. The functional significance of ASIC4 expression in these tissues still awaits clarification
