title: Inhibition of amiloride-sensitive Na+ channel by isothiouronium derivatives.
abstract: The effects on the amiloride-blockable Na+ channel of a family of recently synthesized isothiouronium derivatives were measured in plasma membrane vesicles from rat distal colon. Some of these derivatives act as high-affinity Na(+)-like antagonists on the Na(+)-K(+)-adenosinetriphosphatase. One of the reagents tested, 1-bromo-2,4,6-tris(isothiouronium methyl)-benzene tribromide (Br-TITU), was found to be a potent blocker of the Na+ channel. At neutral pH, Br-TITU rapidly inhibits the channel mediated 22Na+ uptake, with an inhibition constant of 94 +/- 39 nM. The inhibition observed is specific and reversible. 1,3-Dibromo-2,4,6-tris(isothiouronium methyl)benzene tribromide and Br-TITU derivatives with methyl and phenyl substitutions on the isothiouronium moiety were much less effective blockers. Incubation of cells with Br-TITU at alkaline (but not neutral) pH produces irreversible inactivation of channels, possibly due ot covalent modification of a lysine residue. This inactivation can be attenuated by amiloride but not by Na+. Thus Br-TITU may be a useful reagent in identifying essential residues of the channel protein.
authors.affiliation: Department of Membrane Research, Weizmann Institute of Science, Rehovot, Israel.
authors.forename: A
authors.initials: A
authors.lastname: Avigdor
authors.forename: C
authors.initials: C
authors.lastname: Asher
authors.forename: D M
authors.initials: DM
authors.lastname: Tal
authors.forename: S J
authors.initials: SJ
authors.lastname: Karlish
authors.forename: H
authors.initials: H
authors.lastname: Garty
mesh_terms: D000584:Amiloride / Q000494:pharmacology*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002462:Cell Membrane / Q000502:physiology; D003106:Colon; D003907:Dexamethasone / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000502:physiology*; D007550:Isothiuronium / Q000031:analogs & derivatives* / Q000494:pharmacology*; D007700:Kinetics; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000378:metabolism*; D026941:Sodium Channel Blockers; D015222:Sodium Channels / Q000502:physiology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors; D013329:Structure-Activity Relationship
chemical_list: D026941:Sodium Channel Blockers; D015222:Sodium Channels; D007550:Isothiuronium; D000584:Amiloride; D003907:Dexamethasone; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase