TY - JOUR T1 - [<sup>125</sup>I]A-312110, a Novel High-Affinity 1,4-Dihydropyridine ATP-sensitive K<sup>+</sup> Channel Opener: Characterization and Pharmacology of Binding JF - Molecular Pharmacology JO - Mol Pharmacol SP - 143 LP - 153 DO - 10.1124/mol.64.1.143 VL - 64 IS - 1 AU - Rachel Davis-Taber AU - Eduardo J. Molinari AU - Robert J. Altenbach AU - Kristi L. Whiteaker AU - Char-Chang Shieh AU - Gary Rotert AU - Steven A. Buckner AU - John Malysz AU - Ivan Milicic AU - Jeffrey S. McDermott AU - Gary A. Gintant AU - Michael J. Coghlan AU - William A. Carroll AU - Victoria E. Scott AU - Murali Gopalakrishnan Y1 - 2003/07/01 UR - http://molpharm.aspetjournals.org/content/64/1/143.abstract N2 - 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) &gt; N-cyano-N′-(1,1-dimethylpropyl)-N″-3-pyridylguanidine (P1075) &gt; (-)-N-(2-ethoxyphenyl)-N′-(1,2,3-trimethylpropyl)-2-nitroethene-1,1-diamine (Bay X 9228) &gt; pinacidil &gt; (-)-cromakalim &gt; N-(4-benzoyl phenyl)-3,3,3-trifluro-2-hydroxy-2-methylpropionamine (ZD6169) &gt; 9-(3-cyanophenyl)-3,4,6,7,9,10-hexahydro-1,8-(2H,5H)-acridinedione (ZM244085) ≫ diazoxide (16.7 μM). 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. ER -