S‐nitrosoglutathione inhibits cerebrovascular angiotensin II‐dependent and ‐independent AT₁ receptor responses: A possible role of S‐nitrosation

Background and Purpose Angiotensin II (AngII) and NO regulate the cerebral circulation. AngII AT 1 receptors exert ligand‐dependent and ligand‐independent (myogenic tone [MT]) vasoconstriction of cerebral vessels. NO induces post‐translational modifications of proteins such as S ‐nitrosation (redox modification of cysteine residues). In cultured cells, S ‐nitrosation decreases AngII's affinity for the AT 1 receptor. The present work evaluated the functional consequences of S ‐nitrosation on both AngII‐dependent and AngII‐independent cerebrovascular responses. Experimental Approach S ‐Nitrosation was induced in rat isolated middle cerebral arteries by pretreatment with the NO donors, S ‐nitrosoglutathione (GSNO) or sodium nitroprusside (SNP). Agonist‐dependent activation of AT 1 receptors was evaluated by obtaining concentration–response curves to AngII. Ligand‐independent activation of AT 1 receptors was evaluated by calculating MT (active vs. passive diameter) at pressures ranging from 20 to 200 mmHg in the presence or not of a selective AT 1 receptor inverse agonist. Key Results GSNO or SNP completely abolished the AngII‐dependent AT 1 receptor‐mediated vasoconstriction of cerebral arteries. GSNO had no impact on responses to other vasoconstrictors sharing (phenylephrine, U46619) or not (5‐HT) the same signalling pathway. MT was reduced by GSNO, and the addition of losartan did not further decrease MT, suggesting that GSNO blocks AT 1 receptor‐dependent MT. Ascorbate (which reduces S ‐nitrosated compounds) restored the response to AngII but not the soluble GC inhibitor ODQ, suggesting that these effects are mediated by S ‐nitrosation rather than by S ‐nitrosylation. Conclusions and Implications In rat middle cerebral arteries, GSNO pretreatment specifically affects the AT 1 receptor and reduces both AngII‐dependent and AngII‐independent activation, most likely through AT 1 receptor S ‐nitrosation.