Evidence against inhibition of sarcoplasmic reticulum Ca2+-pump as mechanism of H2O2-induced contraction of rat aorta.
OBJECTIVE
To test whether inhibition of sarcoplasmic reticulum (SR) Ca2+-pump is involved in H2O2-induced contraction of endothelium-denuded rat aorta.


METHODS
Isometric tension recording of H2O2 and cyclopiazonic acid (CPA)-induced contractions of rat aortic rings were compared in the absence or presence of various pharmacological tools to discriminate their signaling pathways involved.


RESULTS
Both H2O2 and CPA contracted rat aortic rings, but with different contractile patterns. H2O2 triggered a fast and phasic contraction, whereas CPA elicited a slow and sustained contraction. In Ca2+-free medium, pretreatment of aortic rings with CPA 30 micromol/L but not with H2O2 30 micromol/L nearly abolished phenylephrine (10 micromol/L)-induced contraction. In addition, upon the maximal contraction induced by thapsigargin 30 micromol/L, H2O2 but not CPA further contracted aortic rings. On the other hand, H2O2 (30 micromol/L)- but not CPA (10 micromol/L)-induced contraction could be inhibited by suramin and RB-2 (each 100 micromol/L), two P2-purinoceptor antagonists. Furthermore, although pretreatment with 2-APB, a membrane permeable IP3 receptor blocker, inhibited both H2O2- and CPA-induced contractions, only H2O2 (30 micromol/L)-induced contraction could be depressed, to different degree, by various inhibitors of receptor-coupled or downstream signaling enzymes, including PLC, PKC, PLA2, COX, and protein tyrosine kinases.


CONCLUSIONS
Inhibition of smooth muscle SR Ca2+-pump is unlikely the mechanism responsible for H2O2-induced contraction of endothelium-denuded rat aorta.
Shen
J Z
JZ
Department of Pharmacology, School of Medicine, Zhejiang University, Hangzhou 310031, China. shenjz@mail.hz.zj.cn
Zheng
X F
XF
Wei
E Q
EQ
Kwan
C Y
CY
D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects; D001896:Boron Compounds / Q000494:pharmacology; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism*; D004730:Endothelium, Vascular / Q000502:physiology; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology*; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects; D058919:Purinergic P2 Receptor Antagonists; D051381:Rats; D017207:Rats, Sprague-Dawley; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D013498:Suramin / Q000494:pharmacology
D001896:Boron Compounds; D007211:Indoles; D058919:Purinergic P2 Receptor Antagonists; D013498:Suramin; D006861:Hydrogen Peroxide; C109986:2-aminoethoxydiphenyl borate; D017301:Ca(2+) Mg(2+)-ATPase; C000543:cyclopiazonic acid