MONNA is a selective inhibitor of anoctamin-1 (ANO1; IC50 = 0.08 uM in Xenopus oocytes), a calcium-activated chloride channel (CaCC). It is selective for ANO1 over the chloride channels bestrophin-1, chloride channel protein 2, and cystic fibrosis transmembrane conductance regulator up to 10 uM. MONNA (10 uM) induces full vasorelaxation of preconstricted mouse isolated mesenteric arteries in the presence or absence of chloride. It also hyperpolarizes isolated rat mesenteric arteries under resting conditions.