title: Selective blockade of endothelial Ca2+-activated small- and intermediate-conductance K+-channels suppresses EDHF-mediated vasodilation.
abstract: 1. Activation of Ca(2+)-activated K(+)-channels (K(Ca)) has been suggested to play a key role in endothelium-derived hyperpolarizing factor (EDHF)-mediated vasodilation. However, due to the low selectivity of commonly used K(Ca)-channel blockers it is still elusive which endothelial K(Ca)-subtypes mediate hyperpolarization and thus initiate EDHF-mediated vasodilation. 2. Using the non-cytochrome P450 blocking clotrimazole-derivatives, 1-[(2-chlorophenyl) diphenylmethyl]-1H-pyrazole (TRAM-34) and 2-(2-chlorophenyl)-2,2-diphenylacetonitrile (TRAM-39) as highly selective IK1-inhibitors, we investigated the role of the intermediate-conductance K(Ca) (rIK1) in endothelial hyperpolarization and EDHF-mediated vasodilation. 3. Expression and function of rIK1 and small-conductance K(Ca) (rSK3) were demonstrated in situ in single endothelial cells of rat carotid arteries (CA). rIK1-currents were blocked by TRAM-34 or TRAM-39, while rSK3 was blocked by apamin. In current-clamp experiments, endothelial hyperpolarization in response to acetylcholine was abolished by the combination of apamin and TRAM-34. 4. In phenylephrine-preconstricted CA, acetylcholine-induced NO and prostacyclin-independent vasodilation was almost completely blocked by ChTX, CLT, TRAM-34, or TRAM-39 in combination with the SK3-blocker apamin. Apamin, TRAM-34, and CLT alone or sulphaphenzole, a blocker of the cytochrome P450 isoform 2C9, were ineffective in blocking the EDHF-response. 5. In experiments without blocking NO and prostacyclin synthesis, the combined blockade of SK3 and IK1 reduced endothelium-dependent vasodilation. 6. In conclusion, the use of selective IK1-inhibitors together with the SK3-blocker apamin revealed that activation of both K(Ca), rIK1 and rSK3 is crucial in mediating endothelial hyperpolarization and generation of the EDHF-signal while the cytochrome P450 pathway seems to play a minor or no role in rat CA.
authors.affiliation: Department of Nephrology, Benjamin Franklin Medical Center, Berlin, Germany.
authors.forename: Ines
authors.initials: I
authors.lastname: Eichler
authors.forename: Judith
authors.initials: J
authors.lastname: Wibawa
authors.forename: Ivica
authors.initials: I
authors.lastname: Grgic
authors.forename: Andrea
authors.initials: A
authors.lastname: Knorr
authors.forename: Susanne
authors.initials: S
authors.lastname: Brakemeier
authors.forename: Axel R
authors.initials: AR
authors.lastname: Pries
authors.forename: Joachim
authors.initials: J
authors.lastname: Hoyer
authors.forename: Ralf
authors.initials: R
authors.lastname: Köhler
mesh_terms: D000818:Animals; D001685:Biological Factors / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D026902:Potassium Channel Blockers / Q000494:pharmacology; D024681:Potassium Channels, Calcium-Activated / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology*
chemical_list: D001685:Biological Factors; D026902:Potassium Channel Blockers; D024681:Potassium Channels, Calcium-Activated; C067410:endothelium-dependent hyperpolarization factor