[125I]A-312110, a novel high-affinity 1,4-dihydropyridine ATP-sensitive K+ channel opener: characterization and pharmacology of binding

Mol Pharmacol. 2003 Jul;64(1):143-53. doi: 10.1124/mol.64.1.143.


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.

Publication types

  • Comparative Study

MeSH terms

  • Adenosine Triphosphate / metabolism
  • Animals
  • Binding Sites
  • Dihydropyridines / chemistry
  • Guinea Pigs
  • Heart / drug effects*
  • Iodine Radioisotopes
  • Kinetics
  • Male
  • Membrane Proteins / drug effects
  • Membrane Proteins / metabolism*
  • Myocardium / metabolism
  • Potassium Channels
  • Pyridines / pharmacology*
  • Radioligand Assay
  • Radiopharmaceuticals / pharmacology*
  • Thiophenes / pharmacology*
  • Urinary Bladder / drug effects
  • Urinary Bladder / metabolism


  • (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
  • Dihydropyridines
  • Iodine Radioisotopes
  • Membrane Proteins
  • Potassium Channels
  • Pyridines
  • Radiopharmaceuticals
  • Thiophenes
  • mitochondrial K(ATP) channel
  • 1,4-dihydropyridine
  • Adenosine Triphosphate