title: [125I]A-312110, a novel high-affinity 1,4-dihydropyridine ATP-sensitive K+ channel opener: characterization and pharmacology of binding.
abstract: Although ATP-sensitive K+ channels continue to be explored for their therapeutic potential, developments in high-affinity radioligands to investigate native and recombinant KATP channels have been less forthcoming. This study reports the identification and pharmacological characterization of a novel iodinated 1,4-dihydropyridine KATP channel opener, [125I]A-312110 [(9R)-9-(4-fluoro-3-125iodophenyl)-2,3,5,9-tetrahydro-4H-pyrano[3,4-b]thieno[2,3-e]pyridin-8(7H)-one-1,1-dioxide]. Binding of [125I]A-312110 to guinea pig cardiac (KD = 5.8 nM) and urinary bladder (KD = 4.9 nM) membranes were of high affinity, saturable, and to a single set of binding sites. Displacement of [125I]A-312110 by structurally diverse potassium channel openers (KCOs) indicated a similar rank order of potency in both guinea pig cardiac and bladder membranes (Ki, heart): A-312110 (4.3 nM) > N-cyano-N'-(1,1-dimethylpropyl)-N"-3-pyridylguanidine (P1075) > (-)-N-(2-ethoxyphenyl)-N'-(1,2,3-trimethylpropyl)-2-nitroethene-1,1-diamine (Bay X 9228) > pinacidil > (-)-cromakalim > N-(4-benzoyl phenyl)-3,3,3-trifluro-2-hydroxy-2-methylpropionamine (ZD6169) > 9-(3-cyanophenyl)-3,4,6,7,9,10-hexahydro-1,8-(2H,5H)-acridinedione (ZM244085) >> diazoxide (16.7 microM). Displacement by KATP channel blockers, the sulfonylurea glyburide, and the cyanoguanidine N-[1-(3-chlorophenyl)cyclobutyl]-N'-cyano-N"-3-pyridinyl-guanidine (PNU-99963) were biphasic in the heart but monophasic in bladder with about a 100- to 500-fold difference in Ki values between high- and low-affinity sites. Good correlations were observed between cardiac or bladder-binding affinities of KCOs with functional activation as assessed by their respective potencies to either suppress action potential duration (APD) in Purkinje fibers or to relax electrical field-stimulated bladder contractions. Collectively, these results demonstrate that [125I]A-312110 binds with high affinity and has an improved activity profile compared with other radiolabeled KCOs. [125I]A-312110 is a useful tool for investigation of the molecular and functional properties of the KATP channel complex and for the identification, in a high throughput manner, of both novel channel blockers and openers that interact with cardiac/smooth muscle-type KATP channels.
authors.affiliation: Neuroscience Research, Global Pharmaceutical Research and Development, Abbott Laboratories, Abbott Park, Illinois, USA.
authors.forename: Rachel
authors.initials: R
authors.lastname: Davis-Taber
authors.forename: Eduardo J
authors.initials: EJ
authors.lastname: Molinari
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Altenbach
authors.forename: Kristi L
authors.initials: KL
authors.lastname: Whiteaker
authors.forename: Char-Chang
authors.initials: CC
authors.lastname: Shieh
authors.forename: Gary
authors.initials: G
authors.lastname: Rotert
authors.forename: Steven A
authors.initials: SA
authors.lastname: Buckner
authors.forename: John
authors.initials: J
authors.lastname: Malysz
authors.forename: Ivan
authors.initials: I
authors.lastname: Milicic
authors.forename: Jeffrey S
authors.initials: JS
authors.lastname: McDermott
authors.forename: Gary A
authors.initials: GA
authors.lastname: Gintant
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Coghlan
authors.forename: William A
authors.initials: WA
authors.lastname: Carroll
authors.forename: Victoria E
authors.initials: VE
authors.lastname: Scott
authors.forename: Murali
authors.initials: M
authors.lastname: Gopalakrishnan
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D004095:Dihydropyridines / Q000737:chemistry; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects*; D007457:Iodine Radioisotopes; D007700:Kinetics; D008297:Male; D008565:Membrane Proteins / Q000187:drug effects / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism; D015221:Potassium Channels; D011725:Pyridines / Q000494:pharmacology*; D011869:Radioligand Assay; D019275:Radiopharmaceuticals / Q000494:pharmacology*; D013876:Thiophenes / Q000494:pharmacology*; D001743:Urinary Bladder / Q000187:drug effects / Q000378:metabolism
chemical_list: C475728:(9R)-9-(4-fluoro-3-iodophenyl)-2,3,5,9-tetrahydro-4H-pyrano(3,4-b)thieno(2,3-e)pyridin-8(7H)-one-1,1-dioxide; D004095:Dihydropyridines; D007457:Iodine Radioisotopes; D008565:Membrane Proteins; D015221:Potassium Channels; D011725:Pyridines; D019275:Radiopharmaceuticals; D013876:Thiophenes; C117780:mitochondrial K(ATP) channel; C038806:1,4-dihydropyridine; D000255:Adenosine Triphosphate