Acid-sensing ion channels 1, 2, 3 and 5 (ASIC1, 2, 3 and 5, aka amiloride-sensitive cation channels) are homotrimeric, multi-pass membrane proteins which can transport sodium (Na+) when activated by extracellular protons. Members of the ASIC family are sensitive to amiloride and function in neurotransmission. The encoded proteins function in learning, pain transduction, touch sensation, and development of memory and fear. Many neuronal diseases cause acidosis, accompanied by pain and neuronal damage; ASICs can mediate the pathophysiological effects seen in acidiosis (Wang & Xu 2011, Qadri et al. 2012). The diuretic drug amiloride inhibits these channels, resulting in analgesic effects. NSAIDs (nonsteroidal anti-inflammatory drugs) can also inhibit ASICs to produce analgesia (Voilley et al. 2001). ASICs are also partially permeable to Ca2+, Li+ and K+ (not shown here). ASIC1 and 2 are expressed mostly in brain (Garcia-Anoveros et al. 1997, Price et al. 1996), ASIC3 is strongly expressed in testis (de Weille et al. 1998, Ishibashi & Marumo 1998) and ASIC5 is found mainly in intestine (Schaefer et al. 2000). ASIC4 subunits do not form functional channels and it's activity is unknown. It could play a part in regulating other ASIC activity (Donier et al. 2008).