Na_x sodium channel is expressed in non-myelinating Schwann cells and alveolar type II cells in mice

Na_x is an extracellular sodium-level-sensitive sodium channel expressed in the circumventricular organs in the brain, essential loci for the sodium-level homeostasis in body fluids. Here, we examined the localization of Na_x throughout the visceral organs at the cellular level. In visceral organs including lung, heart, intestine, bladder, kidney and tongue, a subset of Schwann cells within the peripheral nerve trunks were highly positive for Na_x. An electron microscopic study indicated that these Na_x-positive cells were non-myelinating Schwann cells. In the lung, Na_x-positive signals were also observed in the alveolar type II cells, which actively absorb sodium and water to aid gas exchange through the alveolar surface. It was thus suggested that the Na_x sodium channel is involved in controlling the local extracellular sodium level through sodium absorption activity.