It was hypothesized that NaF induces calcium sensitization in Ca(2+)-controlled solution in permeabilized rat mesenteric arteries. Rat mesenteric arteries were permeabilized with beta-escin and subjected to tension measurement. NaF potentiated the concentration-response curves to Ca(2+) (decreased EC(50) and increased E(max)). Cumulative addition of NaF (4.0, 8.0 and 16 mM) also increased vascular tension in Ca(2+)-controlled solution at pCa 7.0 or pCa 6.5, but not at pCa 8.0. NaF-induced vasocontraction and GTPgammaS-induced vasocontraction were not additive. NaF-induced vasocontraction at pCa 7.0 was inhibited by pretreatment with Rho kinase inhibitors H1152 or Y27632 but not with a MLCK inhibitor ML-7 or a PKC inhibitor Ro31-8220. NaF induces calcium sensitization in a Ca(2+)-dependent manner in beta-escin-permeabilized rat mesenteric arteries. These results suggest that NaF is an activator of the Rho kinase signaling pathway during vascular contraction.