title: Delineation of transmembrane domains of the Na+/H+ exchanger that confer sensitivity to pharmacological antagonists.
abstract: Plasma membrane Na+/H+ exchanger (NHE) isoforms NHE1 and NHE3 exhibit very different sensitivities to amiloride and its 5-amino-substituted analogues, benzoyl guanidinium derivatives (e.g. (3-methylsulfonyl-4-piperidinobenzoyl)guanidine methanesulfonate (HOE694)), and cimetidine. To define structural domains that confer differential sensitivity to these antagonists, unique restriction endonuclease sites were engineered into cDNAs for each isoform near the regions that encode the putative membrane-spanning domains. These new sites did not modify their pharmacological properties and allowed several chimeric Na+/H+ exchangers to be constructed by exchanging homologous segments. The modified parental (E1' and E3') and chimeric molecules were stably expressed in exchanger-deficient Chinese hamster ovary AP-1 cells and assayed for their sensitivities to amiloride, ethylisopropylamiloride, HOE694, and cimetidine. Most chimeras showed drug sensitivities corresponding to the dominant parental segment. However, interchanging a 66-amino acid segment containing the putative ninth transmembrane (M9) domain and its adjacent loops caused reciprocal alterations in the sensitivities of E1' and E3' to all antagonists. In addition, substituting the first five putative membrane-spanning domains of E3' with the corresponding region of E1' modestly reduced the transporter's sensitivity to cimetidine but not the other compounds. These data indicate that the protein segment between M8 and M10 may be a major site of interaction with these antagonists, although other regions modestly influence sensitivity to certain drugs.
authors.affiliation: Department of Physiology, McGill University, Montréal, Québec, H3G 1Y6, Canada.
authors.forename: J
authors.initials: J
authors.lastname: Orlowski
authors.forename: R A
authors.initials: RA
authors.lastname: Kandasamy
mesh_terms: D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport; D002927:Cimetidine / Q000494:pharmacology; D018076:DNA, Complementary / Q000235:genetics; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006146:Guanidines / Q000494:pharmacology; D007700:Kinetics; D008024:Ligands; D008562:Membrane Glycoproteins / Q000737:chemistry; D051381:Rats; D011993:Recombinant Fusion Proteins; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors*; D013329:Structure-Activity Relationship; D013450:Sulfones / Q000494:pharmacology
chemical_list: D018076:DNA, Complementary; D004791:Enzyme Inhibitors; D006146:Guanidines; D008024:Ligands; D008562:Membrane Glycoproteins; D011993:Recombinant Fusion Proteins; C000613387:Slc9a3 protein, rat; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D013450:Sulfones; C069139:growth factor-activatable Na-H exchanger NHE-1; C074107:3-methylsulfonyl-4-piperidinobenzoyl guanidine; D000584:Amiloride; D002927:Cimetidine; C039614:ethylisopropylamiloride