 The epithelial sodium channels are structurally and probably evolutionary related to P2X purinoreceptors, pain receptors that activate when they detect ATP.ENaC is located in the apical membrane of polarized epithelial cells in particular in the kidney (primarily in the collecting tubule), the lung, the skin, the male and female reproductive tracts and the colon.Epithelial sodium channels facilitate Na⁺ reabsorption across the apical membranes of epithelia in the distal nephron, respiratory and reproductive tracts and exocrine glands.