Openers of small conductance calcium-activated potassium channels selectively enhance NO-mediated bradykinin vasodilatation in porcine retinal arterioles |
| |
Authors: | T Dalsgaard C Kroigaard M Misfeldt T Bek U Simonsen |
| |
Affiliation: | 1Department of Pharmacology, Aarhus University, Aarhus C, Denmark;2Department of Ophthalmology, Aarhus University Hospital, Aarhus C, Denmark |
| |
Abstract: | Background and purpose:Small (SKCa or KCa2) and intermediate (IKCa or KCa3.1) conductance calcium-activated potassium channels are involved in regulation of vascular tone and blood pressure. The present study investigated whether NS309 (6,7-dichloro-1H-indole-2,3-dione 3-oxime) and CyPPA (cyclohexyl-[2-(3,5-dimethyl-pyrazol-1-yl)-6-methyl-pyrimidin-4-yl]-amine), which are selective openers of SKCa and IKCa channels and of SKCa2 and SKCa3 channels, respectively, enhance endothelium-dependent vasodilatation in porcine retinal arterioles.Experimental approach:In porcine retinal arterioles, SKCa3 and IKCa protein localization was examined by immunolabelling. Endothelial cell calcium was measured by fluorescence imaging. For functional studies, arterioles with internal diameters of 116 ± 2 µm (n = 276) were mounted in microvascular myographs for isometric tension recordings.Key results:SKCa3 and IKCa protein was localized in the endothelium. Bradykinin, but not NS309 or CyPPA increased endothelial cell calcium. Pre-incubation with NS309 or CyPPA enhanced bradykinin relaxation without changing endothelial cell calcium. This enhanced relaxation was abolished by blocking SKCa channels with apamin. In the presence of NS309 or CyPPA, mainly inhibition of NO synthase with asymmetric dimethylarginine, but also inhibition of cyclooxygenase with indomethacin, reduced bradykinin relaxation. Bradykinin relaxation was completely abolished by NO synthase and cyclooxygenase inhibition together with a NO scavenger, oxyhaemoglobin.Conclusions and implications:In porcine retinal arterioles, bradykinin increases endothelial cell calcium leading to activation of SKCa and IKCa channels. Without altering endothelial cell calcium, NS309 and CyPPA open SKCa channels that enhance NO-mediated bradykinin relaxations. These results imply that opening SKCa channels improves endothelium-dependent relaxation and makes this channel a potential target for treatments aimed at restoring retinal blood flow. |
| |
Keywords: | bradykinin CyPPA H2S HOE-140 IKCa NO NS309 prostaglandins retinal arterioles SKCa SNP vasodilatation |
|
|