Use of intermediate/small conductance calcium-activated potassium-channel activator for endothelial protection.
OBJECTIVE
Endothelial dysfunction occurs in hypoxia-related states such as ischemic heart disease or heart surgery. Intermediate- and small-conductance calcium-activated potassium channels (IKCa and SKCa) are closely related to endothelium-dependent hyperpolarizing factor-mediated endothelial function. However, the status of these KCa under hypoxia is unknown. We investigated whether endothelial dysfunction under hypoxic state is related to the alterations of IKCa and SKCa and whether use of IKCa/SKCa activator may protect endothelium from hypoxia-reoxygenation injury.


METHODS
Isometric tension measurement, patch-clamp technique, intracellular membrane potential recording, and molecular methods were used to study porcine coronary arteries and endothelial cells.


RESULTS
Hypoxia-reoxygenation (60-30 minutes) decreased endothelium-dependent hyperpolarizing factor-mediated relaxation at normothermia in Krebs solution (43.3%±6.3% vs 82.3%±2.9%) and in St Thomas' Hospital cardioplegic solution (28.9%±1.8% vs 78.1%±3.0%) (P<.001) as well as at hypothermia in St Thomas' Hospital solution (43.1%±2.6%, P<.001). Hypoxia-reoxygenation markedly reduced endothelial IKCa (2.8±0.6 vs 6.9±0.6 pA/pF) and SKCa currents (1.5±0.3 vs 4.3±0.4 pA/pF) (P<.05) and downregulated endothelial IKCa expression. IKCa/SKCa activator 1-ethyl-2-benzimidazolinone enhanced K+ current in endothelial cells that was blunted by hypoxia. Further, 1-ethyl-2-benzimidazolinone restored (P<.001) endothelium-dependent hyperpolarizing factor-mediated relaxation with hyperpolarization recovered from 6.0±0.3 to 7.8±0.4 mV (P<.05).


CONCLUSIONS
In porcine coronary arteries, hypoxia markedly reduced endothelial K+ currents related to IKCa and SKCa with downregulation of protein expression and endothelium-derived hyperpolarizing factor function. IKCa/SKCa activator may preserve endothelium-dependent hyperpolarizing factor-mediated relaxation with enhancement of K+ current in endothelial cells and cellular membrane potential hyperpolarization in smooth muscle cells and may become a new strategy to protect coronary endothelium in cardiac surgery or transplantation.
Yang
Qin
Q
Department of Surgery, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, NT, Hong Kong. qyang@surgery.cuhk.edu.hk
Huang
Jun-Hao
JH
Man
Yu-Bun
YB
Yao
Xiao-Qiang
XQ
He
Guo-Wei
GW
D000818:Animals; D001562:Benzimidazoles / Q000494:pharmacology*; D001685:Biological Factors / Q000378:metabolism; D015687:Cell Hypoxia; D002478:Cells, Cultured; D003331:Coronary Vessels / Q000187:drug effects* / Q000378:metabolism / Q000503:physiopathology; D004305:Dose-Response Relationship, Drug; D042783:Endothelial Cells / Q000187:drug effects* / Q000378:metabolism; D005260:Female; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels / Q000819:agonists* / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials; D015428:Myocardial Reperfusion Injury / Q000378:metabolism / Q000503:physiopathology / Q000517:prevention & control*; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism*; D026902:Potassium Channel Blockers / Q000494:pharmacology; D051640:Small-Conductance Calcium-Activated Potassium Channels / Q000819:agonists* / Q000378:metabolism; D013552:Swine; D014661:Vasoconstriction / Q000187:drug effects; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014664:Vasodilation / Q000187:drug effects; D014665:Vasodilator Agents / Q000494:pharmacology
D001562:Benzimidazoles; D001685:Biological Factors; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; D026902:Potassium Channel Blockers; D051640:Small-Conductance Calcium-Activated Potassium Channels; D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; C067410:endothelium-dependent hyperpolarization factor; C102635:1-ethyl-2-benzimidazolinone; D011188:Potassium