Mechanism of vasorelaxation and role of endogenous hydrogen sulfide production in mouse aorta

This study aimed to elucidate the molecular mechanism of H2S-induced vasorelaxation. Vasorelaxation responses to the H2S donor NaHS and the H2S precursor L-cysteine were examined by measuring isometric tone of mouse aortic rings in a small vessel myograph. H2S concentrations in Krebs' solution were determined with a polarographic sensor. H2S expression was examined by Western blot, and H2S production from CSE was assayed using a spectroscopic method. In pre-constricted mouse aorta, NaHS (1 mu M-3 mM) elicited vasorelaxation of 95+/-7%, EC50 189+/-69 mu M. This response was unaffected by removal of the endothelium. Maximum vasorelaxation was significantly attenuated by global blockade of K+ channels (50 mM K+) and the K-ATP channel blocker glibenclamide (10 mu M) alone (P<0.01, ANOVA). Specific inhibition of K-Ca, K-IR, or K-V channels elicited a significant shift to the right in the concentration-response curve to NaHS (P<0.01, ANOVA) without affecting maximum relaxation. NaHS-mediated vasorelaxation was inhibited by the Cl- channel inhibitor DIDS (1 mM, P<0.05, t test), and NaHS caused a significant concentration-dependent inhibition of voltage-gated Ca2+ channels (P<0.001, two-way ANOVA). The H2S-producing enzyme cystathionine-gamma-lyase (CSE) was expressed in mouse aorta and had activity of 7+/-3 mu mol H2S/g/min. L-cysteine (1 mu M-3 mM) elicited a CSE-dependent vasorelaxation of mouse aorta with intact endothelium (20+/-7%), but not when the endothelium was removed. CSE inhibitors DL-propargylglycine (20 mM) and beta-cyanoalanine (1 mM) caused concentration-dependent contraction of mouse aorta. In mouse aorta, H2S elicits endothelium-independent vasorelaxation involving several different ion channels and seems to converge at the vascular smooth muscle cell voltage-gated Ca2+ channel. The L-cysteine-CSE-H2S pathway contributes to vasorelaxation and appears to modulate basal vessel tone.