Affiliation:
1. From Physiologisches Institut, Ludwig Maximilians Universität, München, Germany, and INSERM U-533 (G.L.), Faculté des Sciences et Techniques, Nantes, France.
Abstract
Background—
NO-induced dilations in resistance arteries (RAs) are not associated with decreases in vascular smooth muscle cell Ca
2+
. We tested whether a cGMP-dependent activation of the smooth muscle myosin light chain phosphatase (MLCP) resulting in a Ca
2+
desensitization of the contractile apparatus was the underlying mechanism and whether it could be antagonized by the RhoA pathway.
Methods and Results—
The Ca
2+
sensitivity of RA was assessed as the relation between changes in diameter and [Ca
2+
]
i
in depolarized RA (120 mol/L K
+
) exposed to stepwise increases in Ca
2+
ex
(0 to 3 mmol/L). Effects of 10 μmol/L sodium nitroprusside (SNP) on Ca
2+
sensitivity were determined before and after application of the soluble guanylate cyclase inhibitor ODQ (1 μmol/L) and the MLCP inhibitor calyculin A (120 nmol/L) and in presence of the RhoA-activating phospholipid sphingosine-1-phosphate (S1P, 12 nmol/L). SNP-induced dilations were also studied in controls and in RAs pretreated with the Rho kinase inhibitor Y27632 or transfected with a dominant-negative RhoA mutant (N19RhoA). Constrictions elicited by increasing Ca
2+
ex
were significantly attenuated by SNP, which, however, left associated increases in [Ca
2+
]
i
unaffected. This NO-induced attenuation was blocked by ODQ, calyculin A, and S1P. The S1P-induced translocation of RhoA indicating activation of the GTPase was not reversed by SNP. Inhibition of RhoA/Rho kinase by N19RhoA or Y27632 significantly augmented SNP-induced dilations.
Conclusions—
NO dilates RA by activating the MLCP in a cGMP-dependent manner, thereby reducing the apparent Ca
2+
sensitivity of the contractile apparatus. MLCP inactivation via the RhoA/Rho kinase pathway antagonizes this Ca
2+
-desensitizing effect that, in turn, can be restored using RhoA/Rho kinase inhibitors.
Publisher
Ovid Technologies (Wolters Kluwer Health)
Subject
Physiology (medical),Cardiology and Cardiovascular Medicine
Cited by
113 articles.
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