d-Amphetamine inhibits inwardly rectifying potassium channels in Xenopus oocytes expression system.
Effects of d-amphetamine on the renal outer medullary potassium (ROMK1) channels were tested in the Xenopus oocytes expression system. Xenopus oocytes were injected with mRNA coding for wild-type or mutant ROMK1 channels. Giant inside-out patch-clamp recordings were performed. d-Amphetamine inhibited the activity of ROMK1 channels in a manner that was concentration-dependent but voltage-independent. ROMK1 channels are regulated by intracellular pH (pH i) and protein kinase A (PKA). d-Amphetamine decreased the activity of wild-type and pH i gating residue mutant (K80M) channels over a range of pH i values. However, d-amphetamine failed to reduce channel activity in the presence of PKA inhibitors (H89 and KT 5720) and had no inhibitory effect on the mutants of PKA-phosphorylation sites (S44A, S219A, or S313A), mutants that mimicked the negative charge carried by a phosphate group bound to a serine (S44D, S219D, or S313D), or mutant channels with a positive charge (S219R). These findings suggest that d-amphetamine inhibits ROMK1 channels independently of the pH i. The effects of d-amphetamine on ROMK1 channels may be due to a conformational change induced by PKA-mediated phosphorylation, but not to charge-charge interactions.
Department of Pharmacology, College of Medicine, National Taiwan University, Taipei, Taiwan.
Chien-Hsing
CH
Lee
Horng-Huei
HH
Liou
Kuan-Ling
KL
Lu
Yi-Chun
YC
Shen
Ming-Cheng
MC
Tsai
D000818:Animals; D002227:Carbazoles / Q000494:pharmacology; D003913:Dextroamphetamine / Q000494:pharmacology*; D018765:Dopamine Uptake Inhibitors / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation / Q000379:methods; D004791:Enzyme Inhibitors; D005260:Female; D007546:Isoquinolines / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects* / Q000502:physiology / Q000528:radiation effects; D008845:Microinjections; D016297:Mutagenesis, Site-Directed / Q000379:methods; D009865:Oocytes; D018408:Patch-Clamp Techniques; D024661:Potassium Channels, Inwardly Rectifying / Q000235:genetics / Q000502:physiology*; D011758:Pyrroles / Q000494:pharmacology; D012694:Serine / Q000235:genetics / Q000378:metabolism; D013449:Sulfonamides / Q000494:pharmacology; D014981:Xenopus
D002227:Carbazoles; D018765:Dopamine Uptake Inhibitors; D004791:Enzyme Inhibitors; D007546:Isoquinolines; D024661:Potassium Channels, Inwardly Rectifying; D011758:Pyrroles; D013449:Sulfonamides; D012694:Serine; C057416:KT 5720; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide; D003913:Dextroamphetamine