Proton-gated sodium channel; it is activated by a drop of the extracellular pH and then becomes rapidly desensitized. Generates a biphasic current with a fast inactivating and a slow sustained phase. Has high selectivity for sodium ions and can also transport lithium ions with high efficiency. Can also transport potassium ions, but with lower efficiency. It is nearly impermeable to the larger rubidium and cesium ions. Inhibited by the diuretic amiloride. Homotrimer or heterotrimer with other ASIC proteins. Expressed in central nervous system. Expression starts 30 hours post-fertilization (hpf) and is restricted to the anterior and posterior lateral line ganglia and the otic sensory neurons. At 48 hpf expression becomes also evident in the trigeminal ganglia. At 96 hpf expressed throughout most of the central nervous system. Excluded from the dorsal forebrain except for the habenula nuclei. Channel opening involves a conformation change that affects primarily the extracellular domain and the second transmembrane helix and its orientation in the membrane. In the open state, the second transmembrane helix is nearly perpendicular to the plane of the membrane; in the desensitized state it is strongly tilted. Besides, the second transmembrane domain is discontinuously helical in the open state. The GAS motif of the selectivity filter is in an extended conformation, giving rise to a distinct kink in the polypeptide chain. A domain swap between subunits gives rise to a full-length transmembrane helix (By similarity). Belongs to the amiloride-sensitive sodium channel (TC 1.A.6) family. ASIC1 subfamily.