Abstract
We investigated whether the substrate for nitric oxide (NO) production, extracellular l-arginine, contributes to relaxations induced by activating small (SKCa) conductance Ca2+-activated potassium channels. In endothelial cells, acetylcholine increased 3H-l-arginine uptake, while blocking the SKCa and the intermediate (IKCa) conductance Ca2+-activated potassium channels reduced l-arginine uptake. A blocker of the y+ transporter system, l-lysine also blocked 3H-l-arginine uptake. Immunostaining showed co-localization of endothelial NO synthase (eNOS), SKCa3, and the cationic amino acid transporter (CAT-1) protein of the y+ transporter system in the endothelium. An opener of SKCa channels, cyclohexyl-[2-(3,5-dimethyl-pyrazol-1-yl)-6-methyl-pyrimidin-4-yl]-amine (CyPPA) induced large currents in endothelial cells, and concentration-dependently relaxed porcine retinal arterioles. In the presence of l-arginine, concentration-response curves for CyPPA were leftward shifted, an effect unaltered in the presence of low sodium, but blocked by l-lysine in the retinal arterioles. Our findings suggest that SKCa channel activity regulates l-arginine uptake through the y+ transporter system, and we propose that in vasculature affected by endothelial dysfunction, l-arginine administration requires the targeting of additional mechanisms such as SKCa channels to restore endothelium-dependent vasodilatation.
Highlights
Disturbances in retinal blood flow are involved in the pathophysiology of major sight-threatening diseases, such as age-related macular degeneration, primary open angle glaucoma, and diabetic retinopathy [1–4], and involve endothelial dysfunction and impaired endothelium-dependent vasodilatation [5–7]
In isolated porcine retinal arterioles, we studied the effect of l-arginine in the absence and the presence of inhibitors of the cationic amino acid transporter (CAT) system on relaxation induced by bradykinin and CyPPA, an activator of SKCa3 channels [31]
SKCa3 channels in isolated endothelial cells is in close proximity to caveolin-1, endothelial NO synthase (eNOS), and G-protein coupled receptors, such as the bradykinin receptor [37]
Summary
Disturbances in retinal blood flow are involved in the pathophysiology of major sight-threatening diseases, such as age-related macular degeneration, primary open angle glaucoma, and diabetic retinopathy [1–4], and involve endothelial dysfunction and impaired endothelium-dependent vasodilatation [5–7]. In intact vascular preparations, activators of SKCa channels, such as 6,7-Dichloro-1H-indole-2,3-dione 3-oxime (NS309) and cyclohexyl-[2-(3,5-dimethyl-pyrazol-1-yl)-6-methyl-pyrimidin-4-yl]-amine (CyPPA), relax porcine retinal arterioles by a mechanism, which to a large degree are independent of changes in endothelial cell Ca2+ [14]. These findings suggest that other mechanisms contribute to the relaxations induced by the activation of SKCa channels in porcine retinal arterioles. In isolated rabbit eyes, administration of l-arginine decreases ocular vascular tone [26], supporting a major role for l-arginine uptake and NO release in endothelium-dependent relaxation in retinal arterioles. Our findings suggest that SKCa channel activity regulates L-arginine uptake through the y+ transporter system
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
