This protein mediates the voltage-dependent sodium ion permeability of excitable membranes. Assuming opened or closed conformations in response to the voltage difference across the membrane, the protein forms a sodium-selective channel through which Na(+) ions may pass in accordance with their electrochemical gradient . It is a tetrodotoxin-resistant Na(+) channel isoform . This channel is responsible for the initial upstroke of the action potential. Channel inactivation is regulated by intracellular calcium levels .
Cell membrane ; Multi-pass membrane protein . Cytoplasm, perinuclear region . Cell membrane, sarcolemma, T-tubule . RANGRF promotes trafficking to the cell membrane. .
Found in jejunal circular smooth muscle cells (at protein level). Expressed in human atrial and ventricular cardiac muscle but not in adult skeletal muscle, brain, myometrium, liver, or spleen. Isoform 4 is expressed in brain.
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