CLONING, EXPRESSION, AND TISSUE DISTRIBUTION OF A HUMAN AMILORIDE-SENSITIVE NA+ CHANNEL

Amiloride-sensitive Na+ channels control, in part, fluid and electrolyte transport across epithelia in many organs. In the lung, they control the quantity and composition of the respiratory tract fluid and play a key role in the transition from a fluid-filled lung at the time of birth. Their function may also be altered in a number of diseases. The recent identification of an epithelial Na+ channel from rat colon allowed us to use a probe from that sequence to clone an amiloride-sensitive Na+ channel from human kidney, alpha hENaC. The cDNA had an open reading frame of 2,007 nucleotides and encoded a protein predicted to contain 669 amino acids. The amino acid sequence of alpha hENaC was 83% identical to that of the rat. The gene was mapped to chromosome 12 by polymerase chain reaction (PCR) of somatic cell hybrids. Transcripts of alpha hENaC were detected in human kidney, lung, liver, and pancreas. No message was detected in first- and second-trimester human fetal lung, indicating that alpha hENaC expression is developmentally regulated. In vitro transcription and translation of alpha hENaC produced a 74-kDa protein and translation in the presence of microsomal membranes produced a glycosylated 87-kDa protein. Expression of alpha hENaC in Xenopus oocytes produced currents that were amiloride sensitive and Na+ selective, properties consistent with the function of epithelial Na+ channels in native tissues.