Calcium sensitization induced by sodium fluoride in permeabilized rat mesenteric arteries

Abstract

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.

Keywords: Calcium sensitization; Mesenteric artery; Permeabilization; Rho kinase; Sodium fluoride.

Fig. 1

NaF induces Ca²⁺ sensitization in β-escin-permeabilized mesenteric arteries. Representative traces (A) show tension development when β-escin-permeabilized mesenteric arteries were exposed to increasing concentration of free calcium after initial high concentration of calcium (pCa 4.5) in the absence or presence of NaF (4.0, 8.0 or 12 mM). Line graphs (B) show the concentration-response curve to increasing concentration of free calcium (pCa 9.0~5.5) in the absence or presence of NaF (4.0, 8.0 or 12 mM) in β-escin-permeabilized mesenteric arteries. Developed tension is expressed as a percentage of the maximum tension induced by pCa 4.5. Data are expressed as means of 5 experiments with vertical bars showing SEM. ^**p<0.01 vs. Ca²⁺ alone (Repeated measures ANOVA followed by post-hoc Dunnett test).

Fig. 2

NaF induces vasocontraction in Ca²⁺-controlled solution in β-escin- permeabilized mesenteric arteries. Representative traces (A) show tension development when β-escin-permeabilized mesenteric arteries were exposed to cumulative addition of NaF (4.0, 8.0 and 16 mM) at constant concentration of calcium of pCa 8.0, 7.0 or 6.5. Bar graphs (B) show the developed tension elicited by cumulative addition of NaF (4.0, 8.0 and 16 mM) at constant concentration of calcium of pCa 8.0, 7.0 or 6.5 in β-escin-permeabilized mesenteric arteries. When NaF (16 mM)-induced contraction reached plateau, the bathing solutions were replaced with pCa 4.5 solution to obtain maximum contraction. Developed tension is expressed as a percentage of the maximum tension to pCa 4.5. Data are expressed as means of 5 experiments with vertical bars showing SEM.

Fig. 3

Effect of GTPγS on NaF-induced contraction in β-escin-permeabilized mesenteric arteries. Representative traces (A) show tension development when β-escin-permeabilized mesenteric arteries were exposed to addition of 100 µM GTPγS in the absence or presence of NaF (4.0 or 8.0 mM) at constant concentration of calcium of pCa 7.0. Bar graphs (B) show the developed tension elicited by addition of 100 µ M GTPγS in the absence or presence of NaF (4.0 or 12 mM) at constant concentration of calcium of pCa 7.0. When GTPγS (100 µM)-induced contraction reached plateau, the bathing solutions were replaced with pCa 4.5 solutions to obtain maximum contraction. Developed tension is expressed as a percentage of the maximum tension to pCa 4.5. Data are expressed as means of 5 experiments with vertical bars showing SEM. NS, not significant (p>0.05) (One-way ANOVA followed by post-hoc Dunnett test).

Fig. 4

Effect of GDPβS on NaF-induced contraction in β-escin-permeabilized mesenteric arteries. Representative traces (A) show tension development when β-escin-permeabilized mesenteric arteries were exposed to addition of 8.0 mM NaF or 100 µM GTPγS following 300 µM GDPβS at constant concentration of calcium of pCa 7.0. Representative traces (B) show tension development when β-escin-permeabilized mesenteric arteries were exposed to addition of 8.0 mM NaF or 100 µM GTPγS in the absence or presence of 300 µM GDPβS at constant concentration of calcium of pCa 7.0. When GTPγS (100 µM)-or NaF (8.0 mM)-induced contraction reached plateau, the bathing solutions were replaced with pCa 4.5 solutions to obtain maximum contraction. The traces are representative of four experiments.

Fig. 5

Effect of Rho kinase inhibitors, Y27632 and H1152 on NaF-induced vasocontraction in β-escin-permeabilized mesenteric arteries. Representative traces (A) show tension development when β-escin-permeabilized mesenteric arteries were exposed to addition of 8.0 mM NaF in the absence or presence of Rho kinase inhibitors, Y27632 or H1152, at constant concentration of calcium of pCa 7.0. Bar graphs (B) show the developed tension elicited by addition of 8.0 mM NaF in the absence or presence of Rho kinase inhibitors, Y27632 or H1152, at constant concentration of calcium of pCa 7.0 in β-escin-permeabilized mesenteric arteries. When NaF (8.0 mM)-induced contraction reached plateau, the bathing solutions were replaced with pCa 4.5 solution to obtain maximum contraction. Developed tension is expressed as a percentage of the maximum tension to pCa 4.5. Data are expressed as means of 5 experiments with vertical bars showing SEM. ^**p<0.01 vs. vehicle (One-way ANOVA followed by post-hoc Dunnett test).

Fig. 6

Effect of ML-7 or Ro31-8220 on NaF-induced vasocontraction in β-escin-permeabilized mesenteric arteries. Representative traces (A) show tension development when β-escin-permeabilized mesenteric arteries were exposed to addition of 8.0 mM NaF in the absence or presence of MLCK inhibitor ML-7 or PKC inhibitor Ro31-8220 at constant concentration of calcium of pCa 7.0. Bar graphs (B) show the developed tension elicited by addition of 8.0 mM NaF in the absence or presence of MLCK inhibitor ML-7 or PKC inhibitor Ro31-8220 at constant concentration of calcium of pCa 7.0 in β-escin-permeabilized mesenteric arteries. When NaF (8.0 mM)-induced contraction reached plateau, the bathing solutions were replaced with pCa 4.5 solution to obtain maximum contraction. Developed tension is expressed as a percentage of the maximum tension to pCa 4.5. Data are expressed as means of 5 experiments with vertical bars showing SEM. NS, not significant (p>0.05) (One-way ANOVA followed by post-hoc Dunnett test).