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Trovafloxacin, a fluroquinolone antibiotic, was recently found to be an inhibitor of pannexin-1 channels through which ATP is released as “find-me” signals in apoptotic Jurkat cells. Our interest in the role of pannexin-1 channels in α₁-adrenoceptor-mediated vasoconstriction led us to the novel finding reported here. Concentration-response curves to methoxamine and phenylephrine were competitively antagonised by trovafloxacin (1–30 µM) with a pK_B of 5.54 and 5.32, respectively, in rat mesenteric small arteries isolated for myography. In comparison, prazosin (1–10 nM) antagonised methoxamine concentration-response curves with a pK_B of 9.76. Trovafloxacin (1–30 µM) had no effect on either the thromboxane mimetic (U46619) or endothelin-1 concentration-contraction curves. Interestingly, the concentration range is similar for trovafloxacin antagonising the 3 distinct pharmacological targets: (i) fourth generation …