ABSTRACT
Aim To investigate the effect of protein kinase C (PKCs) on midazolam-induced relaxation of aortic smooth muscle in spontaneously hypertensive rats (SHR) and the underlying mechanism. Methods U-sing the isolated vessel tension measurement system, the relaxant effect of midazolam on aortic smooth muscle of SHR and Wistar-Kyoto (WKY) rats was observed. After preincubation with GF109203X (GF, a broad-spectrum inhibitor of PKCs), LY333531 (LY, PKCp2 specific inhibitor) and PKC6 pseudo-substrate inhibitor (PPS), the changes of midazolam-induced relaxation amplitude were observed. Western blot was used to detect the effect of midazolam on the phosphorylation level of PKC [32 in SHR aortic smooth muscle. The effect of midazolam, LY, GF and PPS on the phosphorylation level of the key proteins (CPI-17/ MYPT1/MLC) in calcium sensitization pathway in SHR aortic smooth muscle was also examined. Results Midazolam concentration-dependently relaxed aortic smooth muscle in SHR and WKY. GF significantly inhibited midazolam-induced relaxation amplitude of SHR and WKY aortic smooth muscle. LY and PPS had no significant effect on midazolam-induced relaxation amplitude of WKY aortic smooth muscle. In contrast, LY markedly inhibited midazolam-induced relaxation amplitude of SHR aortic smooth muscle. Midazolam significantly inhibited the phosphorylation level of PKC [32 enhanced by NE in SHR aortic smooth muscle. Midazolam, LY and GF all evidently inhibited the phosphorylation level of the key proteins in calcium sensitization pathway enhanced by NE in SHR aortic smooth muscle. Conclusions Midazolam induces excessive relaxation of SHR aortic smooth muscle by inhibiting calcium sensitization pathway mediated by PKC [32.
ABSTRACT
BACKGROUND: A toxic dose of bupivacaine produces vasodilation in isolated aortas. The goal of this in vitro study was to investigate the cellular mechanism associated with bupivacaine-induced vasodilation in isolated endotheliumdenuded rat aortas precontracted with phenylephrine. METHODS: Isolated endothelium-denuded rat aortas were suspended for isometric tension recordings. The effects of nifedipine, verapamil, iberiotoxin, 4-aminopyridine, barium chloride, and glibenclamide on bupivacaine concentration-response curves were assessed in endothelium-denuded aortas precontracted with phenylephrine. The effect of phenylephrine and KCl used for precontraction on bupivacaine-induced concentration-response curves was assessed. The effects of verapamil on phenylephrine concentration-response curves were assessed. The effects of bupivacaine on the intracellular calcium concentration ([Ca2+]i) and tension in aortas precontracted with phenylephrine were measured simultaneously with the acetoxymethyl ester of a fura-2-loaded aortic strip. RESULTS: Pretreatment with potassium channel inhibitors had no effect on bupivacaine-induced relaxation in the endothelium-denuded aortas precontracted with phenylephrine, whereas verapamil or nifedipine attenuated bupivacaine-induced relaxation. The magnitude of the bupivacaine-induced relaxation was enhanced in the 100 mM KCl-induced precontracted aortas compared with the phenylephrine-induced precontracted aortas. Verapamil attenuated the phenylephrine-induced contraction. The magnitude of the bupivacaine-induced relaxation was higher than that of the bupivacaine-induced [Ca2+]i decrease in the aortas precontracted with phenylephrine. CONCLUSIONS: Taken together, these results suggest that toxic-dose bupivacaine-induced vasodilation appears to be mediated by decreased calcium sensitization in endothelium-denuded aortas precontracted with phenylephrine. In addition, potassium channel inhibitors had no effect on bupivacaine-induced relaxation. Toxic-dose bupivacaine- induced vasodilation may be partially associated with the inhibitory effect of voltage-operated calcium channels.
Subject(s)
Animals , Rats , 4-Aminopyridine , Aorta , Barium , Bupivacaine , Calcium Channels , Calcium , Glyburide , Nifedipine , Phenylephrine , Potassium Channels , Relaxation , Vasodilation , VerapamilABSTRACT
It was hypothesized that NaF induces calcium sensitization in Ca2+-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 Ca2+ (decreased EC50 and increased E(max)). Cumulative addition of NaF (4.0, 8.0 and 16 mM) also increased vascular tension in Ca2+-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 Ca2+-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.