title: Renal epithelial protein (Apx) is an actin cytoskeleton-regulated Na+ channel.
abstract: Apx, the amphibian protein associated with renal amiloride-sensitive Na+ channel activity and with properties consistent with the pore-forming 150-kDa subunit of an epithelial Na+ channel complex initially purified by Benos et al. (Benos, D. J., Saccomani, G., and Sariban-Sohraby, S.(1987) J. Biol. Chem. 262, 10613-10618), has previously failed to generate amiloride-sensitive Na+ currents (Staub, O., Verrey, F., Kleyman, T. R., Benos, D. J., Rossier, B. C., and Kraehenbuhl, J.-P.(1992) J. Cell Biol. 119, 1497-1506). Renal epithelial Na+ channel activity is tonically inhibited by endogenous actin filaments (Cantiello, H. F., Stow, J., Prat, A. G., and Ausiello, D. A.(1991) Am. J. Physiol. 261, C882-C888). Thus, Apx was expressed and its function examined in human melanoma cells with a defective actin-based cytoskeleton. Apx-transfection was associated with a 60-900% increase in amiloride-sensitive (Ki = 3 microM) Na+ currents. Single channel Na+ currents had a similar functional fingerprint to the vasopressin-sensitive, and actin-regulated epithelial Na+ channel of A6 cells, including a 6-7 pS single channel conductance and a perm-selectivity of Na+:K+ of 4:1. Na+ channel activity was either spontaneous, or induced by addition of actin or protein kinase A plus ATP to the bathing solution of excised inside-out patches. Therefore, Apx may be responsible for the ionic conductance involved in the vasopressin-activated Na+ reabsorption in the amphibian kidney.
authors.affiliation: Renal Unit, Massachusetts General Hospital East, Charlestown, Massachusetts 02129, USA.
authors.forename: A G
authors.initials: AG
authors.lastname: Prat
authors.forename: E J
authors.initials: EJ
authors.lastname: Holtzman
authors.forename: D
authors.initials: D
authors.lastname: Brown
authors.forename: C C
authors.initials: CC
authors.lastname: Cunningham
authors.forename: I L
authors.initials: IL
authors.lastname: Reisin
authors.forename: T R
authors.initials: TR
authors.lastname: Kleyman
authors.forename: M
authors.initials: M
authors.lastname: McLaughlin
authors.forename: G R
authors.initials: GR
authors.lastname: Jackson
authors.forename: J
authors.initials: J
authors.lastname: Lydon
authors.forename: H F
authors.initials: HF
authors.lastname: Cantiello
mesh_terms: D000199:Actins / Q000378:metabolism*; D000584:Amiloride / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D001692:Biological Transport; D003599:Cytoskeleton / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004553:Electric Conductivity; D004848:Epithelium; D006801:Humans; D007668:Kidney / Q000378:metabolism; D008545:Melanoma; D008969:Molecular Sequence Data; D011485:Protein Binding; D011994:Recombinant Proteins / Q000378:metabolism; D015222:Sodium Channels / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D029867:Xenopus Proteins; D014982:Xenopus laevis
chemical_list: D000199:Actins; D011994:Recombinant Proteins; C078824:Shroom1 protein, Xenopus; D015222:Sodium Channels; D029867:Xenopus Proteins; D000584:Amiloride