Hydrogen sulfide dilates rat mesenteric arteries by activating endothelial large-conductance Ca²⁺-activated K⁺ channels and smooth muscle Ca²⁺ sparks

• Published in: American journal of physiology. Heart and circulatory physiology Vol. 304; no. 11; p. H1446
• Main Authors: Jackson-Weaver, Olan, Osmond, Jessica M, Riddle, Melissa A, Naik, Jay S, Gonzalez Bosc, Laura V, Walker, Benjimen R, Kanagy, Nancy L
• Format: Journal Article
• Language: English
• Published: United States 01-06-2013
• Subjects: Analysis of Variance; Aniline Compounds; Animals; Calcium Signaling - drug effects; Cytochrome P-450 Enzyme Inhibitors; Cytochrome P-450 Enzyme System - metabolism; Electrophysiological Phenomena; Endothelium, Vascular - drug effects; Endothelium, Vascular - metabolism; Fluorescent Dyes; Hydrogen Sulfide - pharmacology; Immunohistochemistry; In Vitro Techniques; Large-Conductance Calcium-Activated Potassium Channels - drug effects; Male; Mesenteric Arteries - drug effects; Microelectrodes; Muscle, Smooth, Vascular - drug effects; Patch-Clamp Techniques; Potassium Channel Blockers - pharmacology; Rats; Rats, Sprague-Dawley; Vasodilator Agents; Xanthenes; cytochrome P-450 epoxygenase; sodium hydrosulfide; membrane potential
• ISSN: 1522-1539
• DOI: 10.1152/ajpheart.00506.2012

We have previously shown that hydrogen sulfide (H₂S) reduces myogenic tone and causes relaxation of phenylephrine (PE)-constricted mesenteric arteries. This effect of H₂S to cause vasodilation and vascular smooth muscle cell (VSMC) hyperpolarization was mediated by large-conductance Ca(2+)-activated potassium channels (BKCa). Ca(2+) sparks are ryanodine receptor (RyR)-mediated Ca(2+)-release events that activate BKCa channels in VSMCs to cause membrane hyperpolarization and vasodilation. We hypothesized that H₂S activates Ca(2+) sparks in small mesenteric arteries. Ca(2+) sparks were measured using confocal microscopy in rat mesenteric arteries loaded with the Ca(2+) indicator fluo-4. VSMC membrane potential (Em) was measured in isolated arteries using sharp microelectrodes. In PE-constricted arteries, the H₂S donor NaHS caused vasodilation that was inhibited by ryanodine (RyR blocker), abluminal or luminal iberiotoxin (IbTx, BKCa blocker), endothelial cell (EC) disruption, and sulfaphenazole [cytochrome P-450 2C (Cyp2C) inhibitor]. The H₂S donor NaHS (10 μmol/l) increased Ca(2+) sparks but only in the presence of intact EC and this was blocked by sulfaphenazole or luminal IbTx. Inhibiting cystathionine γ-lyase (CSE)-derived H2S with β-cyano-l-alanine (BCA) also reduced VSMC Ca(2+) spark frequency in mesenteric arteries, as did EC disruption. However, excess CSE substrate homocysteine did not affect spark activity. NaHS hyperpolarized VSMC Em in PE-depolarized mesenteric arteries with intact EC and also hyperpolarized EC Em in arteries cut open to expose the lumen. This hyperpolarization was prevented by ryanodine, sulfaphenazole, and abluminal or luminal IbTx. BCA reduced IbTx-sensitive K(+) currents in freshly dispersed mesenteric ECs. These results suggest that H₂S increases Ca(2+) spark activity in mesenteric artery VSMC through activation of endothelial BKCa channels and Cyp2C, a novel vasodilatory pathway for this emerging signaling molecule.