title: Conductive sodium pathway with low affinity to amiloride in LLC-PK1 cells and other epithelia.
abstract: Electrical potential driven 22Na+ fluxes were measured in membrane vesicles prepared from a number of cultured and naturally occurring epithelia. In all preparations a rheogenic pathway blocked by 200 microM (but not by 1.5 microM) amiloride was noted. This transporter was characterized in membranes prepared from cultured LLC-PK1 cells. In this preparation more than 50% of the rheogenic 22Na+ uptake was blocked by amiloride (IC50 approximately 30 microM), phenamil (IC50 approximately 66 microM), or ethylisopropylamiloride (IC50 approximately 5 microM). This amiloride-sensitive flux was not seen if the vesicles were partially depolarized by external Na+ or K+. It could not be driven by a pH gradient, did not require the presence of Ca2+, sugars, or amino acids, and showed little dependence on temperature (25 versus 0 degrees C). The data suggest the existence of an epithelial amiloride-blockable Na+ transporter different from the previously characterized Na+ channel, Na+/H+ and Na+/Ca2+ exchangers, and the Na+-hexose co-transporter. In rat kidney cortex membranes prepared by Mn2+ precipitation, this transporter is primarily located in the brush-border fraction.
authors.affiliation: Physiology Department, Faculty of Health Science, Ben Gurion University, Beer Sheva, Israel.
authors.forename: A
authors.initials: A
authors.lastname: Moran
authors.forename: C
authors.initials: C
authors.lastname: Asher
authors.forename: E J
authors.initials: EJ
authors.lastname: Cragoe
authors.forename: H
authors.initials: H
authors.lastname: Garty
mesh_terms: D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology*; D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism; D004910:Erythrocyte Membrane / Q000378:metabolism; D005260:Female; D006801:Humans; D007672:Kidney Cortex / Q000378:metabolism; D007700:Kinetics; D008297:Male; D008564:Membrane Potentials; D008871:Microvilli / Q000378:metabolism; D011817:Rabbits; D011895:Rana ridibunda; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000187:drug effects / Q000502:physiology*; D014634:Valinomycin / Q000494:pharmacology
chemical_list: D015222:Sodium Channels; D014634:Valinomycin; C047088:phenylamil; D000584:Amiloride; D012964:Sodium; C039614:ethylisopropylamiloride