title: Role of potassium and calcium channels in sevoflurane-mediated vasodilation in the foeto-placental circulation.
abstract: BACKGROUND
  Sevoflurane has been demonstrated to vasodilate the foeto-placental vasculature. We aimed to determine the contribution of modulation of potassium and calcium channel function to the vasodilatory effect of sevoflurane in isolated human chorionic plate arterial rings.
  
  
  METHODS
  Quadruplicate ex vivo human chorionic plate arterial rings were used in all studies. Series 1 and 2 examined the role of the K+ channel in sevoflurane-mediated vasodilation. Separate experiments examined whether tetraethylammonium, which blocks large conductance calcium activated K+ (KCa++) channels (Series 1A+B) or glibenclamide, which blocks the ATP sensitive K+ (KATP) channel (Series 2), modulated sevoflurane-mediated vasodilation. Series 3 - 5 examined the role of the Ca++ channel in sevoflurane induced vasodilation. Separate experiments examined whether verapamil, which blocks the sarcolemmal voltage-operated Ca++ channel (Series 3), SK&F 96365 an inhibitor of sarcolemmal voltage-independent Ca++ channels (Series 4A+B), or ryanodine an inhibitor of the sarcoplasmic reticulum Ca++ channel (Series 5A+B), modulated sevoflurane-mediated vasodilation.
  
  
  RESULTS
  Sevoflurane produced dose dependent vasodilatation of chorionic plate arterial rings in all studies. Prior blockade of the KCa++ and KATP channels augmented the vasodilator effects of sevoflurane. Furthermore, exposure of rings to sevoflurane in advance of TEA occluded the effects of TEA. Taken together, these findings suggest that sevoflurane blocks K+ channels. Blockade of the voltage-operated Ca++channels inhibited the vasodilator effects of sevoflurane. In contrast, blockade of the voltage-independent and sarcoplasmic reticulum Ca++channels did not alter sevoflurane vasodilation.
  
  
  CONCLUSIONS
  Sevoflurane appears to block chorionic arterial KCa++ and KATP channels. Sevoflurane also blocks voltage-operated calcium channels, and exerts a net vasodilatory effect in the in vitro foeto-placental circulation.
authors.affiliation: Department of Anaesthesia, Clinical Sciences Institute, National University of Ireland, Galway Ireland. john.laffey@nuigalway.ie.
authors.forename: James
authors.initials: J
authors.lastname: Jarman
authors.forename: Chrisen H
authors.initials: CH
authors.lastname: Maharaj
authors.forename: Brendan D
authors.initials: BD
authors.lastname: Higgins
authors.forename: Rachel F
authors.initials: RF
authors.lastname: Farragher
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Laffey
authors.forename: Noel M
authors.initials: NM
authors.lastname: Flynn
authors.forename: John G
authors.initials: JG
authors.lastname: Laffey