Modulation of endothelial Ca(2+)-activated K(+) channels by oxidized LDL and its contribution to endothelial proliferation.
OBJECTIVE
Oxidized low-density lipoprotein (oxLDL) plays an important role in causing endothelial dysfunction and initiating atherosclerosis. Some of the endothelial functions have been shown to be modulated by changes in cellular electrophysiological properties. Therefore, we analysed the effect of oxLDL on endothelial Ca(2+)-activated K(+) channels (BK(Ca)) and its contribution to oxLDL-mediated changes of proliferation and syntheses of nitric oxide (NO).


METHODS
The patch-clamp technique was used to study the behavior of BK(Ca) in human endothelial cells of umbilical cord veins (HUVEC). Changes of intracellular Ca(2+) were measured by means of Fura-2 imaging. Cell counts and [3H]-thymidine incorporation were used to analyse endothelial proliferation. Synthesis of NO was measured by means of [3H]-cGMP radioimmunoassay.


RESULTS
oxLDL (10 microg/ml) caused a significant increase of BK(Ca) activity, whereas preincubation of HUVEC with an antibody against the lectin-like-oxLDL-receptor-1 (LOX-1) abolished BK(Ca) activation. Fura-2 measurements revealed a biphasic increase of intracellular Ca(2+) after application of the atherogenic lipid. Endothelial proliferation was significantly increased by oxLDL. The highly selective BK(Ca) inhibitor iberiotoxin (100 nmol/l IBX) blocked this proliferative response. Acetylcholine-induced NO synthesis was significantly decreased by IBX. Interestingly, oxLDL significantly decreased acetylcholine-induced NO synthesis if the production of superoxide was not blocked by antisense oligonucleotides against the NAD(P)H-oxidase.


CONCLUSIONS
Our data demonstrate that oxLDL activates BK(Ca), which plays an important role in oxLDL-mediated endothelial proliferation. Acetylcholine-induced NO synthesis is modulated by BK(Ca), whereas the reduction of acetylcholine-induced NO-synthesis by oxLDL is related to an increase in superoxide production.
Kuhlmann
Christoph Rüdiger Wolfram
CR
Department of Cardiology and Angiology, Justus-Liebig-University of Giessen, Germany.
Schäfer
Matthias
M
Li
Fang
F
Sawamura
Tatsuya
T
Tillmanns
Harald
H
Waldecker
Bernd
B
Wiecha
Johannes
J
D000109:Acetylcholine / Q000494:pharmacology; D001161:Arteriosclerosis / Q000378:metabolism* / Q000473:pathology; D002118:Calcium / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D008077:Lipoproteins, LDL / Q000378:metabolism / Q000494:pharmacology*; D009569:Nitric Oxide / Q000378:metabolism; D018408:Patch-Clamp Techniques; D024681:Potassium Channels, Calcium-Activated / Q000378:metabolism*
D008077:Lipoproteins, LDL; D024681:Potassium Channels, Calcium-Activated; C099252:oxidized low density lipoprotein; D009569:Nitric Oxide; D000109:Acetylcholine; D002118:Calcium