Enhancement of Rho/Rho-kinase system in regulation of vascular smooth muscle contraction in tachycardia-induced heart failure

OBJECTIVE: The Rho/Rho-kinase system regulates Ca(2+) sensitivity in vascular smooth muscle. A new drug, Y-27632, specifically inhibits Rho-kinase and hence decreases the phosphorylation of myosin light chain, thus reducing contraction. Here, we compare the effects of Y-27632 and nifedipine on the vasoconstrictor response of the femoral artery in heart failure. METHODS: Heart failure (HF) was produced by chronic rapid RV pacing (250 bpm, 28 days, six dogs). Indo1-AM was loaded into endothelium-denuded femoral artery segments for measuring intracellular [Ca(2+)]. Tension and changes in intracellular [Ca(2+)] [the change in the ratio (418 nm/468 nm) of Indo1 fluorescence (F(ratio))] were simultaneously measured in Krebs-Ringer solution. RESULTS: In HF: (i) norepinephrine (10 microM) produced greater tension (784+/-52 g/cm(2)) than in control (502+/-64 g/cm(2)) despite a similar increase in F(ratio), indicating increased Ca(2+) sensitivity in vascular smooth muscle; (ii) nifedipine attenuated this enhanced response by only a maximum of 27% at 1 micromol/l with a 56% reduction in F(ratio); (iii) Y-27632 attenuated it by a maximum of 80% at 100 micromol/l without a significant change in F(ratio); (iv) RhoA protein and mRNA expression levels in the femoral artery were up-regulated by +110% and +56%, respectively, while those of Rho-kinase were unchanged. CONCLUSIONS: The Ca(2+)-sensitizing mechanism involving the Rho/Rho-kinase system may be deeply involved in the enhanced arterial vasoconstriction seen in HF. Since Y-27632 attenuated this response in small arteries, it shows potential as a novel, potent vasodilator for the treatment of HF.