Shear stress-induced up-regulation of the intermediate-conductance Ca(2+)-activated K(+) channel in human endothelium.
OBJECTIVE
Wall shear stress associated with blood flow is a major stimuli for generation of endothelial vasodilating and antithrombotic factors and it also regulates endothelial gene expression. Activation of endothelial intermediate-conductance Ca(2+)-activated K(+) channels (IK(Ca)) is important for the control of endothelial function by inducing cell hyperpolarization and thus generation of the endothelium-derived hyperpolarizing factor. In the present study we tested whether the IK(Ca) encoding IKCa1 gene is regulated by laminar shear stress (LSS).


METHODS
Human umbilical vein endothelial cells (HUVEC) were subjected to LSS with a magnitude of 0.5-15 dyn/cm(2) and time intervals of 2-24 h in a flow cone apparatus. Expression of the IKCa1 gene and IK(Ca)-functions were determined by using real time RT-PCR and patch-clamp techniques.


RESULTS
A short 2-4 h-or long 24 h-exposure to a LSS with a low (venous) magnitude of 0.5 dyn/cm(2) had no effect on IKCa1 expression levels. An exposure for 2 and 4 h to LSS with an intermediate magnitude of 5 dyn/cm(2) was also ineffective, whereas an exposure for 24 h induced a significant threefold up-regulation of IKCa1 expression levels. An exposure to LSS with a higher (arterial) magnitude of 15 dyn/cm(2), resulted in an eightfold up-regulation of IKCa1 expression levels after a 4 h-exposure and a fourfold increase of IKCa1 expression levels at 24 h. The increased IKCa1 expression levels following exposure to high levels of LSS resulted in enhanced IK(Ca) whole-cell currents and in an increased hyperpolarization of the endothelium in response to ATP and the IK(Ca) opener 1-EBIO. Inhibition of the mitogen-activated protein kinase/extracellular-signal-regulated kinase (ERK) kinase 1/2 (MEK/ERK) pathway by PD98059 prevented the LSS-induced up-regulation of IKCa1 expression levels and IK(Ca) whole-cell currents indicating that augmentation of IKCa1 expression levels is mediated by the LSS-induced activation of the MEK/ERK pathway.


CONCLUSIONS
Long term exposure to LSS up-regulates expression and function of endothelial IK(Ca). This increase might represent a new important mechanism in endothelial adaptation to altered hemodynamics.
Brakemeier
Susanne
S
Department of Nephrology, Charité-Universitätsmedizin Berlin, Campus Benjamin Franklin, Hindenburgdamm 30, D-12200 Berlin, Germany.
Kersten
Anne
A
Eichler
Ines
I
Grgic
Ivica
I
Zakrzewicz
Andreas
A
Hopp
Hartmut
H
Köhler
Ralf
R
Hoyer
Joachim
J
D002478:Cells, Cultured; D042783:Endothelial Cells / Q000502:physiology*; D004730:Endothelium, Vascular / Q000166:cytology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D024681:Potassium Channels, Calcium-Activated / Q000235:genetics* / Q000502:physiology; D011725:Pyridines / Q000494:pharmacology; D012039:Regional Blood Flow; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects; D013314:Stress, Mechanical; D014471:Umbilical Veins
D004791:Enzyme Inhibitors; D005419:Flavonoids; D007093:Imidazoles; D024681:Potassium Channels, Calcium-Activated; D011725:Pyridines; C093642:SB 203580; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one