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Selective blockade of endothelial Ca 2+ ‐activated small‐ and intermediate‐conductance K + ‐channels suppresses EDHF‐mediated vasodilation
Author(s) -
Eichler Ines,
Wibawa Judith,
Grgic Ivica,
Knorr Andrea,
Brakemeier Susanne,
Pries Axel R,
Hoyer Joachim,
Köhler Ralf
Publication year - 2003
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1038/sj.bjp.0705075
Subject(s) - apamin , charybdotoxin , hyperpolarization (physics) , vasodilation , endothelium derived hyperpolarizing factor , chemistry , prostacyclin , iberiotoxin , potassium channel , channel blocker , endothelium , pharmacology , endocrinology , medicine , biophysics , membrane potential , biochemistry , biology , stereochemistry , calcium , organic chemistry , nuclear magnetic resonance spectroscopy
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. Using the non‐cytochrome P450 blocking clotrimazole‐derivatives, 1‐[(2‐chlorophenyl) diphenylmethyl]‐1 H ‐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. 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. 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. In experiments without blocking NO and prostacyclin synthesis, the combined blockade of SK3 and IK1 reduced endothelium‐dependent vasodilation. 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.British Journal of Pharmacology (2003) 138 , 594–601. doi: 10.1038/sj.bjp.0705075