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. Inhibited by Cs(1+) ions. Inhibited by the spider venom psalmotoxin-1; this locks the channel into its desensitized conformation. Channel activity is increased by the heterodimeric snake venom neurotoxin composed of MitTx-alpha and MitTx-beta; this slows channel closure and increases the magnitude of the steady-state current that is triggered by low pH. Homotrimer. Interacts with spider venom psalmotoxin 1 with a one to one stoichiometry. Interacts with the heterodimeric snake venom neurotoxin composed of MitTx-alpha and MitTx-beta. 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. Belongs to the amiloride-sensitive sodium channel (TC 1.A.6) family. ASIC1 subfamily.