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Effect of potassium channel openers on mitochondrial activity in endothelial cells

Agnieszka Łojek 1,2,  Antoni Wrzosek 2,  Adam M. Szewczyk 2,  Paweł Gwóźdź 3,  Stefan Chłopicki 3,  Krzysztof Dołowy 1

1. Warsaw Agricultural University (SGGW), Nowoursynowska 166, Warszawa 02-787, Poland
2. Nencki Institute of Experimental Biology, Pasteura 3, Warszawa 02-093, Poland
3. Department of Experimental Pharmacology, Medical College of Jagiellonian University, Kraków 31-531, Poland

Abstract
It is well documented that potassium channels openers have cytoprotective role in ischemia/reperfusion events. We studied the effect of large conductance potassium channels (BKCa) openers on calcium homeostasis and mitochondrial activity in endothelial cell line EA.hy 926, the cell line derived by fusing human umbilical vein endothelial cells with the cell line A549. We tested the action of potassium channels openers on mitochondrial activity in endothelial cells. It was observed that NS1619 decelerated the rate of respiration in EA.hy 926 endothelial cells as measured with oxygen electrode. CGS7184, conversely, accelerated rate of respiration in endothelial cells. Further studies were performed to investigate the changes in mitochondrial electrical activity, namely mitochondrial membrane potential. Both CGS7184 and NS1619 induced a drop in mitochondrial membrane potential as measured with the use of JC-1 fluorescent indicator. We also tested NS1619 and CGS7184, BKCa openers, on calcium homeostasis in EA.hy 926 cells, as measured with FURA-2 fluorescent indicator. We found that both NS1619 and CGS7184 caused an increase in Ca2+ level in a concentration-dependent manner. Moreover, the effect of CGS7184 and NS1619 on calcium transient was additive. However, CGS7184 but not NS1619, besides discharging endoplasmic reticulum caused calcium influx from external medium, as observed with FURA-2 quenching by manganese ions, which suggests different targets for these potassium channels openers action. When calcium ions were absent in the external medium CGS7184 and NS1619 caused release of Ca2+ from internal stores. It was supported with experiments performed on isolated endoplasmic reticulum vesicles. The influence of CGS7184 on sarcoplasmic reticulum Ca2+-ATP-ase was checked, and it was noticed that CGS7184 did not inhibit Ca2+-ATP-ase as compared with Thapsigargin, sarcoplasmic reticulum Ca2+-ATP-ase inhibitor. Our results suggest that beside potassium channels opening activities CGS7184 and NS1619 have pleiotropic actions on EA.hy 926 cells causing increase in intracellular calcium level, influencing the respiration and mitochondrial membrane potential.

This work was supported by Polish Mitochondrial Network MitoNet.pl

 

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Presentation: Wykład at Zjazd Polskiego Towarzystwa Biochemicznego, Sympozjum H, by Agnieszka Łojek
See On-line Journal of Zjazd Polskiego Towarzystwa Biochemicznego

Submitted: 2007-04-26 11:29
Revised:   2009-06-07 00:44