Different molecular sites of action for the KATP channel inhibitors, PNU-99963 and PNU-37883A.
1. We investigated the mechanism of action of two novel nonsulphonylurea ATP-sensitive potassium channel (K(ATP)) inhibitors, PNU-99963 and PNU-37883A, on four types of cloned K(ATP) channels. 2. Whole-cell currents were recorded in a symmetrical potassium (140 mM) gradient in HEK-293 cells stably expressing Kir6.2/SUR1, Kir6.2/SUR2A, Kir6.2/SUR2B or Kir6.1/SUR2B. 3. PNU-99963 potently inhibited the four K(ATP) channel clones. The concentration at which half-maximum current was inhibited (IC(50)) was 66, 41, 43 and 11 nM for Kir6.2/SUR1, Kir6.2/SUR2A, Kir6.2/SUR2B and Kir6.1/SUR2B, respectively. In contrast, PNU-99963 up to a concentration of 3 microM had no significant effect on current generated in HEK-293 cells by transiently expressing Kir6.2Delta26, a C-terminal truncated pore-forming subunit of Kir6.2. 4. PNU-37883A inhibited four types of K(ATP) channels, but to different extents. Inhibition of the putative smooth muscle K(ATP) channel types, Kir6.2/SUR2B (IC(50); 15 microM) and Kir6.1/SUR2B (IC(50); 6 microM), was significantly greater than inhibition of either the pancreatic beta cell or cardiac K(ATP) channel clones. Moreover, PNU-37883A significantly inhibited currents generated by expressing Kir6.2Delta26 alone, with an IC(50) of 5 microM, which was significantly increased to 38 microM when Kir6.2Delta26 was expressed with SUR2B. 5. In conclusion, two structurally different nonsulphonylurea compounds, PNU-99963 and PNU-37883A, inhibit K(ATP) channels via different mechanisms, namely through the sulphonylurea receptor (SUR) and the pore-forming subunits, respectively, although SUR2B reduced the inhibitory effect of PNU-37883A. While PNU-99963 potently inhibits all the four cloned K(ATP) channels, PNU-37883A has a degree of selectivity towards both smooth muscle K(ATP) channels, but could not discriminate between them.
Cui
Yi
Y
Centre for Clinical Pharmacology, BHF Laboratories, Department of Medicine, University College London, 5 University Street, London WC1E 6JJ, U.K.
Tinker
Andrew
A
Clapp
Lucie H
LH
D018528:ATP-Binding Cassette Transporters / Q000502:physiology; D000255:Adenosine Triphosphate / Q000502:physiology*; D000631:Aminopyridines / Q000494:pharmacology*; D002460:Cell Line; D003001:Cloning, Molecular; D004305:Dose-Response Relationship, Drug; D006146:Guanidines / Q000494:pharmacology*; D006801:Humans; D007515:Islets of Langerhans / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008775:Methylprednisolone / Q000031:analogs & derivatives* / Q000494:pharmacology*; D009130:Muscle, Smooth / Q000502:physiology; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology*; D015221:Potassium Channels / Q000502:physiology; D024661:Potassium Channels, Inwardly Rectifying / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000502:physiology; D021122:Protein Subunits / Q000037:antagonists & inhibitors / Q000502:physiology; D011955:Receptors, Drug / Q000502:physiology; D064233:Sulfonylurea Receptors; D014162:Transfection
C577507:ABCC8 protein, human; C577510:ABCC9 protein, human; D018528:ATP-Binding Cassette Transporters; D000631:Aminopyridines; D006146:Guanidines; C109642:PNU 99963; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D021122:Protein Subunits; D011955:Receptors, Drug; D064233:Sulfonylurea Receptors; D000255:Adenosine Triphosphate; C052305:methylprednisolone suleptanate; D008775:Methylprednisolone