title: Role of intracellular Ca2+ in the expression of the amiloride-sensitive epithelial sodium channel.
abstract: The amiloride-sensitive epithelial sodium channel (ENaC), a multimeric plasma membrane protein composed of alpha-, beta-, and gamma-ENaC subunits, mediates Na(+) reabsorption in epithelial tissues, including the distal nephron, colon, lung, and secretory glands, and plays a critical role in pathophysiology of essential hypertension and cystic fibrosis (CF). The function of ENaC is tightly regulated by signals elicited by aldosterone, vasopressin, agents that increase intracellular cAMP levels, ions, ion channels, G-protein-coupled mechanisms, and cytoskeletal proteins. In this paper, the effects of Ca(2+) on the expression of the human ENaC subunits expressed in human embryonic kidney cells (HEK-293 cells) were examined. Incubation of cells with increased extracellular Ca(2+) and treatment of cells with A23187 and thapsigargin stimulated the expression of the monomeric ENaC subunits. Treatment of cells with Ca(2+)-chelating agents, EGTA and BAPTA-AM, reduced the levels of ENaC subunit expression. The pulse-chase experiments suggested that a rise in the intracellular Ca(2+) increases the ENaC subunit expression. Immunoblot analysis using the anti-ubiquitin antibody indicated that ENaC undergoes ubiquitination. A correlation between the processes that regulate ENaC function with the intracellular Ca(2+) was discussed.
authors.affiliation: Department of Biochemistry and Molecular Biology, 984525 Nebraska Medical Center, Omaha, NE 68198-4525, USA. usrao@unmc.edu
authors.forename: U Subrahmanyeswara
authors.initials: US
authors.lastname: Rao
authors.forename: James M
authors.initials: JM
authors.lastname: Baker
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Pluznick
authors.forename: Premalatha
authors.initials: P
authors.lastname: Balachandran
mesh_terms: D000595:Amino Acid Sequence; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D002460:Cell Line; D003001:Cloning, Molecular; D003600:Cytosol / Q000378:metabolism; D053503:Epithelial Sodium Channels; D006801:Humans; D007668:Kidney / Q000166:cytology; D008969:Molecular Sequence Data; D008970:Molecular Weight; D021122:Protein Subunits / Q000096:biosynthesis; D011994:Recombinant Proteins / Q000096:biosynthesis; D015222:Sodium Channels / Q000096:biosynthesis*; D019284:Thapsigargin / Q000494:pharmacology
chemical_list: D053503:Epithelial Sodium Channels; D021122:Protein Subunits; D011994:Recombinant Proteins; D015222:Sodium Channels; D000001:Calcimycin; D019284:Thapsigargin; D002118:Calcium