Extracellular alkalinization induces endothelium-derived nitric oxide dependent relaxation in rat thoracic aorta.
OBJECTIVE
To investigate the mechanism through which the extracellular alkalinization promotes relaxation in rat thoracic aorta.


METHODS
The relaxation response to NaOH-induced extracellular alkalinization (7.4-8.5) was measured in aortic rings pre-contracted with phenylephrine (Phe, 10(-6) M). The vascular reactivity experiments were performed in endothelium-intact and -denuded rings, in the presence or and absence of indomethacin (10(-5) M), NG-nitro-l-arginine methyl ester (L-NAME, 10(-4) M), N-(6-Aminohexyl)-5-chloro-1-naphthalenesulfonamide/HCl (W-7, 10(-7) M), 2,5-dimethylbenzimidazole (DMB, 2×10(-5) M) and methyl-β-cyclodextrin (10(-2) M). In addition, the effects of NaOH-induced extracellular alkalinization (pH 8.0 and 8.5) on the intracellular nitric oxide (NO) concentration was evaluated in isolated endothelial cells loaded with diaminofluorescein-FM diacetate (DAF-FM DA, 5 μM), in the presence and absence of DMB (2×10(-5) M).


RESULTS
The extracellular alkalinization failed to induce any change in vascular tone in aortic rings pre-contracted with KCl. In rings pre-contracted with Phe, the extracellular alkalinization caused relaxation in the endothelium-intact rings only, and this relaxation was maintained after cyclooxygenase inhibition; completely abolished by the inhibition of nitric oxide synthase (NOS), Ca(2+)/calmodulin and Na(+)/Ca(2+) exchanger (NCX), and partially blunted by the caveolae disassembly.


CONCLUSIONS
These results suggest that, in rat thoracic aorta, that extracellular alkalinization with NaOH activates the NCX reverse mode of endothelial cells in rat thoracic aorta, thereby the intracellular Ca(2+) concentration and activating the Ca(2+)/calmodulin-dependent NOS. In turn, NO is released promoting relaxation.
Celotto
A C
AC
Laboratory of Endothelial Function, Department of Surgery and Anatomy, School of Medicine, University of São Paulo, Ribeirão Preto, SP, Brazil.
Capellini
V K
VK
Restini
C B A
CB
Baldo
C F
CF
Bendhack
L M
LM
Evora
P R B
PR
D000818:Animals; D001013:Aorta, Thoracic / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000378:metabolism; D042783:Endothelial Cells / Q000187:drug effects* / Q000378:metabolism*; D005110:Extracellular Space / Q000187:drug effects / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000378:metabolism; D010656:Phenylephrine / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D012972:Sodium Hydroxide / Q000494:pharmacology*; D019831:Sodium-Calcium Exchanger / Q000187:drug effects / Q000378:metabolism
D002147:Calmodulin; D019831:Sodium-Calcium Exchanger; D010656:Phenylephrine; D009569:Nitric Oxide; D012972:Sodium Hydroxide; D019001:Nitric Oxide Synthase; D002118:Calcium