Vascular KCNQ potassium channels as novel targets for the control of mesenteric artery constriction by vasopressin, based on studies in single cells, pressurized arteries, and in vivo measurements of mesenteric vascular resistance

Pressor effects of the vasoconstrictor hormone arginine vasopressin ( AVP), observed when systemic AVP concentrations are less than 100 pM, are important for the physiological maintenance of blood pressure, and they are also the basis for therapeutic use of vasopressin to restore blood pressure in hypotensive patients. However, the mechanisms by which circulating AVP induces arterial constriction are unclear. We examined the novel hypothesis that KCNQ potassium channels mediate the physiological vasoconstrictor actions of AVP. Reverse transcriptase polymerase chain reaction revealed expression of KCNQ1, KCNQ4, and KCNQ5 in rat mesenteric artery smooth muscle cells ( MASMCs). Whole- cell perforated patch recordings of voltage-sensitive K+ (K-v) currents in freshly isolated MASMCs revealed 1,3-dihydro1- phenyl-3,3- bis( 4- pyridinylmethyl)- 2H- indol- 2-one ( linopirdine)- and 10,10- bis( 4- pyridinylmethyl)- 9( 10H)- anthracenone (XE- 991)- sensitive KCNQ currents that were electrophysiologically and pharmacologically distinct from other K-v currents. Suppression of KCNQ currents by AVP (100pM) was associated with significant membrane depolarization, and it was abolished by the protein kinase C ( PKC) inhibitor calphostin C ( 250 nM). The KCNQ channel blocker linopirdine ( 10 mu M) inhibited KCNQ currents in MASMCs, and it induced constriction of isolated rat mesenteric arteries. The vasoconstrictor responses were not additive when combined with 30 pM AVP, and they were prevented by the L- type Ca2(+) channel blocker verapamil. Ethyl-N-[2-amino- 6-( 4fluorophenylmethylamino) pyridin- 3- yl] carbamic acid ( flupirtine) significantly enhanced KCNQ currents, and it reversed constrictor responses to 30 pM AVP. In vivo, i. v. administration of linopirdine induced a dose- dependent increase in mesenteric artery resistance and blood pressure, whereas flupirtine had the opposite effects. We conclude that physiological concentrations of AVP induce mesenteric artery constriction via PKCdependent suppression of KCNQ currents and L- type Ca2(+) channel activation in MASMCs.