Bimodal effects of the Kv7 channel activator retigabine on vascular K+ currents.
OBJECTIVE
This study investigated the functional and electrophysiological effects of the Kv7 channel activator, retigabine, on murine portal vein smooth muscle.


METHODS
KCNQ gene expression was determined by reverse transcriptase polymerase chain reaction (RT-PCR) and immunocytochemical experiments. Whole cell voltage clamp and current clamp were performed on isolated myocytes from murine portal vein. Isometric tension recordings were performed on whole portal veins. K+ currents generated by KCNQ4 and KCNQ5 expression were recorded by two-electrode voltage clamp in Xenopus oocytes.


RESULTS
KCNQ1, 4 and 5 were expressed in mRNA derived from murine portal vein, either as whole tissue or isolated myocytes. Kv7.1 and Kv7.4 proteins were identified in the cell membranes of myocytes by immunocytochemistry. Retigabine (2-20 microM) suppressed spontaneous contractions in whole portal veins, hyperpolarized the membrane potential and augmented potassium currents at -20 mV. At more depolarized potentials, retigabine and flupirtine, decreased potassium currents. Both effects of retigabine were prevented by prior application of the K(v)7 blocker XE991 (10 muM). Recombinant KCNQ 4 or 5 channels were only activated by retigabine or flupirtine.


CONCLUSIONS
The Kv7 channel activators retigabine and flupirtine have bimodal effects on vascular potassium currents, which are not seen with recombinant KCNQ channels. These results provide support for KCNQ4- or KCNQ5-encoded channels having an important functional impact in the vasculature.
Division of Basic Medical Sciences, Ion Channels and Cell Signalling Research Centre, St George's University of London, London, UK.
Sym
S
Yeung
M
M
Schwake
V
V
Pucovský
Ia
Ia
Greenwood
D000631:Aminopyridines / Q000494:pharmacology; D000818:Animals; D000873:Anthracenes / Q000494:pharmacology; D002219:Carbamates / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D051656:KCNQ Potassium Channels / Q000819:agonists* / Q000235:genetics / Q000378:metabolism; D051657:KCNQ1 Potassium Channel / Q000819:agonists / Q000378:metabolism; D008564:Membrane Potentials; D051379:Mice; D008807:Mice, Inbred BALB C; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000378:metabolism; D032389:Myocytes, Smooth Muscle / Q000187:drug effects* / Q000378:metabolism; D010655:Phenylenediamines / Q000494:pharmacology*; D011169:Portal Vein / Q000187:drug effects / Q000378:metabolism; D011188:Potassium / Q000378:metabolism*; D026902:Potassium Channel Blockers / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D011994:Recombinant Proteins / Q000819:agonists / Q000378:metabolism; D013997:Time Factors; D014661:Vasoconstriction / Q000187:drug effects; D014665:Vasodilator Agents / Q000494:pharmacology*; D014982:Xenopus laevis
C112297:10,10-bis(4-pyridinylmethyl)-9(10H)-anthracenone; D000631:Aminopyridines; D000873:Anthracenes; D002219:Carbamates; D051656:KCNQ Potassium Channels; D051657:KCNQ1 Potassium Channel; C506326:KCNQ5 channel, mouse; C496910:Kcnq1 protein, mouse; C492167:Kcnq4 protein, mouse; D010655:Phenylenediamines; D026902:Potassium Channel Blockers; D012333:RNA, Messenger; D011994:Recombinant Proteins; D014665:Vasodilator Agents; C101866:ezogabine; C034161:flupirtine; D011188:Potassium