title: Inhibitory profile of SEA0400 [2-[4-[(2,5-difluorophenyl)methoxy]phenoxy]-5-ethoxyaniline] assessed on the cardiac Na+-Ca2+ exchanger, NCX1.1.
abstract: SEA0400 (2-[4-[(2,5-difluorophenyl)methoxy]phenoxy]-5-ethoxyaniline) has recently been described as a potent and selective inhibitor of Na(+)-Ca(2+) exchange in cardiac, neuronal, and renal preparations. The inhibitory effects of SEA0400 were investigated on the cloned cardiac Na(+)-Ca(2+) exchanger, NCX1.1, expressed in Xenopus laevis oocytes to gain insight into its inhibitory mechanism. Na(+)-Ca(2+) exchange currents were measured using the giant excised patch technique using conditions to evaluate both inward and outward currents. SEA0400 inhibited outward Na(+)-Ca(2+) exchange currents with high affinity (IC(50) = 78 +/- 15 and 23 +/- 4 nM for peak and steady-state currents, respectively). Considerably less inhibitory potency (i.e., micromolar) was observed for inward currents. The inhibitory profile was reexamined after proteolytic treatment of excised patches with alpha-chymotrypsin, a procedure that eliminates ionic regulatory mechanisms. After this treatment, an IC(50) value of 1.2 +/- 0.6 microM was estimated for outward currents, whereas inward currents became almost insensitive to SEA0400. The inhibitory effects of SEA0400 on outward exchange currents were evident at both high and low concentrations of regulatory Ca(2+), although distinct features were noted. SEA0400 accelerated the inactivation rate of outward currents. Based on paired pulse experiments, SEA0400 altered the recovery of exchangers from the Na(+)(i)-dependent inactive state, particularly at higher regulatory Ca(2+)(i) concentrations. Finally, the inhibitory potency of SEA0400 was strongly dependent on the intracellular Na(+) concentration. Our data confirm that SEA0400 is the most potent inhibitor of the cardiac Na(+)-Ca(2+) exchanger described to date and provide a reasonable explanation for its apparent transport mode selectivity.
authors.affiliation: Institute of Cardiovascular Sciences, St. Boniface Hospital Research Centre, 351 Tache Avenue, Winnipeg, Manitoba, Canada R2H 2A6.
authors.forename: Candace
authors.initials: C
authors.lastname: Lee
authors.forename: Neeraj S
authors.initials: NS
authors.lastname: Visen
authors.forename: Naranjan S
authors.initials: NS
authors.lastname: Dhalla
authors.forename: Hoa Dinh
authors.initials: HD
authors.lastname: Le
authors.forename: Michael
authors.initials: M
authors.lastname: Isaac
authors.forename: Platon
authors.initials: P
authors.lastname: Choptiany
authors.forename: Gil
authors.initials: G
authors.lastname: Gross
authors.forename: Alexander
authors.initials: A
authors.lastname: Omelchenko
authors.forename: Toshio
authors.initials: T
authors.lastname: Matsuda
authors.forename: Akemichi
authors.initials: A
authors.lastname: Baba
authors.forename: Kenzo
authors.initials: K
authors.lastname: Takahashi
authors.forename: Mark
authors.initials: M
authors.lastname: Hnatowich
authors.forename: Larry V
authors.initials: LV
authors.lastname: Hryshko
mesh_terms: D000814:Aniline Compounds / Q000494:pharmacology* / Q000627:therapeutic use; D000818:Animals; D051379:Mice; D010647:Phenyl Ethers / Q000494:pharmacology* / Q000627:therapeutic use; D015427:Reperfusion Injury / Q000378:metabolism / Q000517:prevention & control; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D014982:Xenopus laevis
chemical_list: D000814:Aniline Compounds; D010647:Phenyl Ethers; C430918:SEA 0400; D019831:Sodium-Calcium Exchanger