Nitric oxide-induced decrease in calcium sensitivity of resistance arteries is attributable to activation of the myosin light chain phosphatase and antagonized by the RhoA/Rho kinase pathway.
BACKGROUND
NO-induced dilations in resistance arteries (RAs) are not associated with decreases in vascular smooth muscle cell Ca2+. We tested whether a cGMP-dependent activation of the smooth muscle myosin light chain phosphatase (MLCP) resulting in a Ca2+ desensitization of the contractile apparatus was the underlying mechanism and whether it could be antagonized by the RhoA pathway.


RESULTS
The Ca2+ sensitivity of RA was assessed as the relation between changes in diameter and [Ca2+]i in depolarized RA (120 mol/L K+) exposed to stepwise increases in Ca2+ex (0 to 3 mmol/L). Effects of 10 micromol/L sodium nitroprusside (SNP) on Ca2+ sensitivity were determined before and after application of the soluble guanylate cyclase inhibitor ODQ (1 micromol/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 Ca2+ex were significantly attenuated by SNP, which, however, left associated increases in [Ca2+]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 Ca2+ sensitivity of the contractile apparatus. MLCP inactivation via the RhoA/Rho kinase pathway antagonizes this Ca2+-desensitizing effect that, in turn, can be restored using RhoA/Rho kinase inhibitors.
Bolz
Steffen-Sebastian
SS
Physiologisches Institut der Ludwig Maximilians Universität, Schillerstrasse 44, 80336 München, Germany. bolz@lrz.uni-muenchen.de
Vogel
Lukas
L
Sollinger
Daniel
D
Derwand
Roland
R
de Wit
Cor
C
Loirand
Gervaise
G
Pohl
Ulrich
U
D036002:ADP Ribose Transferases / Q000096:biosynthesis / Q000235:genetics / Q000494:pharmacology; D000818:Animals; D001158:Arteries / Q000187:drug effects* / Q000502:physiology; D001905:Botulinum Toxins / Q000096:biosynthesis / Q000235:genetics / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D006224:Cricetinae; D006152:Cyclic GMP / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D066298:In Vitro Techniques; D047908:Intracellular Signaling Peptides and Proteins; D008246:Lysophospholipids; D009132:Muscles / Q000098:blood supply; D016297:Mutagenesis, Site-Directed; D043263:Myosin-Light-Chain Phosphatase; D009569:Nitric Oxide / Q000494:pharmacology*; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000187:drug effects / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D014162:Transfection; D014654:Vascular Patency / Q000187:drug effects / Q000502:physiology; D014655:Vascular Resistance / Q000187:drug effects / Q000502:physiology; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014665:Vasodilator Agents / Q000494:pharmacology; D054460:rho-Associated Kinases; D020742:rhoA GTP-Binding Protein / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*
D004791:Enzyme Inhibitors; D047908:Intracellular Signaling Peptides and Proteins; D008246:Lysophospholipids; D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; C060506:sphingosine 1-phosphate; D009569:Nitric Oxide; D036002:ADP Ribose Transferases; C063007:exoenzyme C3, Clostridium botulinum; D017346:Protein Serine-Threonine Kinases; D054460:rho-Associated Kinases; D010749:Phosphoprotein Phosphatases; D043263:Myosin-Light-Chain Phosphatase; D001905:Botulinum Toxins; D020742:rhoA GTP-Binding Protein; D006152:Cyclic GMP; D013110:Sphingosine; D002118:Calcium