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. Isoform 3 discrimates stronger than isoform 1 between monovalent cations. Isoform 3 can flux Ca(2+) while isoform 1 cannot. Heteromeric channels composed of isoform 2 and isoform 3 are active but have a lower pH-sensitivity. Mediates glutamate-independent Ca(2+) entry into neurons upon acidosis. This Ca(2+) overloading is toxic for cortical neurons and may be in part responsible for ischemic brain injury. Heteromeric channel assembly seems to modulate channel properties.

Cation channel with high affinity for sodium, which is gated; by extracellular protons and inhibited by the diuretic amiloride. Also; permeable for Li(+) and K(+). Activation by an extracellular pH drop is; followed by a rapid pH-independent inactivation. Heteromeric channel; assembly seems to modulate channel properties.