An investigation of the mechanisms of hydrogen sulfide-induced vasorelaxation in rat middle cerebral arteries

Hydrogen sulfide (H2S) is an endogenous mediator with peripheral vasorelaxant effects; however, the mechanism of H2S-induced vasorelaxation in cerebral blood vessels has not been extensively studied. Vasorelaxation studies were performed on middle cerebral arteries from male Sprague Dawley rats using wire myography. Immunofluorescence staining was used to detect the presence of the H2S-producing enzyme cystathionine-gamma-lyase (CSE). CSE was present in the endothelium and smooth muscle of middle cerebral arteries. The CSE substrate, l-cysteine, induced vasorelaxation that was sensitive to the CSE inhibitor dl-propargylglycine. This relaxation was independent of endothelium, suggesting that H2S was produced in the vascular smooth muscle. The H2S donor, sodium hydrogen sulfide (NaHS; 0.1-3.0 mM) produced concentration-dependent relaxation, which was unaffected by endothelium removal. Nifedipine (3 mu M) significantly reduced the maximum relaxation elicited by NaHS. Inhibiting potassium (K+) conductance with 50 mM K+ significantly attenuated NaHS-induced relaxation, however, selective blockers of ATP sensitive (K-ATP), calcium sensitive (K-Ca), voltage dependent (K-V), or inward rectifier (K-ir) channels alone or in combination did not affect the response to NaHS. 4,4-diisothiocyanatostilbene-2,2-disulfonic acid (DIDS; 300 mu M) caused a significant rightward shift of the NaHS concentration-response curve, but this effect could not be explained by inhibition of Cl- channels or Cl-/ HCO (3) (-) exchange, as selective blockade of these mechanisms had no effect. These findings suggest endogenous H2S can regulate cerebral vascular function. The H2S-mediated relaxation of middle cerebral arteries is DIDS sensitive and partly mediated by inhibition of l-type calcium channels, with an additional contribution by K channels but not K-ATP, K-Ca, K-V, or K-ir subtypes.