Résumé
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.