Synthesis and characterization of a novel tritiated KATP channel opener with a benzopyran structure.
The synthesis of a tritiated benzopyran-type opener of the ATP-dependent K+ channel (KATP channel), [3H]-PKF217 - 744 (3S,4R)-N-[3,4-dihydro-2,2-dimethyl-3-hydroxy-6-(2-methyl-4-pyridinyl)-2H-1-benzopyran-4-yl]-3-[2,6-3H]pyridinecarboxamide with a specific activity of 50 Ci mmol(-1) is described. Binding of the ligand was studied in membranes from human embryonic kidney cells transfected with the sulphonylurea receptor isoforms, SUR2B and SUR2A, respectively. PKF217 - 744 was confirmed as being a KATP channel opener by its ability to open the Kir6.1/SUR2B channel, the recombinant form of the vascular KATP channel, and to inhibit binding of the pinacidil analogue, [3H]-P1075, to SUR2B (Ki=26 nM). The kinetics of [3H]-PKF217 - 744 binding to SUR2B was described by rate constants of association and dissociation of 6.9x10(6) M(-1) min(-1) and 0.09 min(-1), respectively. Binding of [3H]-PKF217 - 744 to SUR2B/2A was activated by MgATP (EC50 approximately 3 microM) and inhibited (SUR2B) or enhanced (SUR2A) by MGADP: Binding of [3H]-PKF217 - 744 to SUR2B was inhibited by representatives of the different structural classes of openers and sulphonylureas. Ki values were identical with those obtained using the opener [3H]-P1075 as the radioligand. Glibenclamide accelerated dissociation of the SUR2B-[3H]-PKF217 - 744 complex. The data show that the affinity of [3H]-PKF217 - 744 binding to SUR2B is approximately 6 times lower than that of [3H]-P1075. This is due to a surprisingly slow association rate of the benzopyran-type ligand, suggesting a complex mechanism of opener binding to SUR. The other pharmacological properties of the two opener radioligands are identical.
Manley
P W
PW
Preclinical Research, Novartis Pharma Ltd., CH-4057 Basel, Switzerland.
Löffler-Walz
C
C
Russ
U
U
Hambrock
A
A
Moenius
T
T
Quast
U
U
D018528:ATP-Binding Cassette Transporters; D000465:Algorithms; D000818:Animals; D001578:Benzopyrans / Q000737:chemistry / Q000494:pharmacology*; D001667:Binding, Competitive / Q000187:drug effects; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D054086:KATP Channels; D007700:Kinetics; D009131:Muscle, Smooth, Vascular / Q000187:drug effects; D018408:Patch-Clamp Techniques; D011169:Portal Vein / Q000187:drug effects; D015221:Potassium Channels / Q000819:agonists*; D024661:Potassium Channels, Inwardly Rectifying; D011725:Pyridines / Q000494:pharmacology*; D011869:Radioligand Assay; D051381:Rats; D011994:Recombinant Proteins; D014162:Transfection
D018528:ATP-Binding Cassette Transporters; D001578:Benzopyrans; D054086:KATP Channels; C431514:N-(3,4-dihydro-2,2-dimethyl-3-hydroxy-6-(2-methyl-4-pyridinyl)-2H-1-benzopyran-4-yl)-3-(2,6-3H)pyridinecarboxamide; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011725:Pyridines; D011994:Recombinant Proteins; C092520:uK-ATP-1 potassium channel