[125I]A-312110, a novel high-affinity 1,4-dihydropyridine ATP-sensitive K+ channel opener: characterization and pharmacology of binding.
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.
Davis-Taber
Rachel
R
Neuroscience Research, Global Pharmaceutical Research and Development, Abbott Laboratories, Abbott Park, Illinois, USA.
Molinari
Eduardo J
EJ
Altenbach
Robert J
RJ
Whiteaker
Kristi L
KL
Shieh
Char-Chang
CC
Rotert
Gary
G
Buckner
Steven A
SA
Malysz
John
J
Milicic
Ivan
I
McDermott
Jeffrey S
JS
Gintant
Gary A
GA
Coghlan
Michael J
MJ
Carroll
William A
WA
Scott
Victoria E
VE
Gopalakrishnan
Murali
M
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
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