title: Na(+)/H(+) exchanger inhibitor induces vasorelaxation through nitric oxide production in endothelial cells via intracellular acidification-associated Ca2(+) mobilization.
abstract: The objective of this study was to determine the mechanism by which Na(+)/H(+) exchanger (NHE) inhibitors induce vasodilatation. The NHE inhibitors, 5-(N,N-dimethyl)-amiloride (DMA), cariporide, and amiloride, evoked endothelium-dependent relaxation in rat aortas with ED50 values of 16, 89, and 148μM, respectively, and these effects were abolished by treatment with N(G)-nitro-l-arginine methyl ester (L-NAME). The relaxation effects induced by DMA and cariporide were strongly attenuated in aortas of the endothelial NO synthase (eNOS)-deficient mice, as compared to the effects in wild-type mice. The DMA-induced relaxation in rat aorta was attenuated by a calmodulin (CaM) inhibitor, calmidazolium, and a soluble guanylyl cyclase inhibitor, [1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, but was not affected by a phosphoinositide 3-kinase inhibitor, wortmannin. Immunoblots for endothelial eNOS on immunoprecipitated CaM complexes showed that DMA enhanced the association of eNOS with CaM in rat aortas. Both DMA and cariporide induced the reduction of intracellular pH (pHi) in bovine aortic endothelial cells (BAECs), which was accompanied by a sustained elevation of cytosolic Ca(2+) ([Ca(2+)]i). This DMA-induced rise of [Ca(2+)]i was not affected by removing external Ca(2+) from the buffer, but was abolished in thapsigargin-pretreated BAECs. These results suggest that lowering of pHi by NHE inhibitors in endothelial cells induces the mobilization of Ca(2+) from the thapsigargin-sensitive stores of endoplasmic reticulum, which in turn stimulates NO production via the CaM-dependent activation of eNOS.
authors.affiliation: Laboratory of Cardiovascular Pharmacology, Department of Biopharmaceutical Sciences, Kobe Gakuin University, Minatojima 1-1-3, Chuo-ku, Kobe 650-8586, Japan.
authors.forename: Tomoya
authors.initials: T
authors.lastname: Sasahara
authors.forename: Katsutoshi
authors.initials: K
authors.lastname: Yayama
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Matsuzaki
authors.forename: Masato
authors.initials: M
authors.lastname: Tsutsui
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Okamoto
mesh_terms: D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000378:metabolism; D002417:Cattle; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism; D006146:Guanidines / Q000494:pharmacology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism*; D052250:Nitric Oxide Synthase Type III / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors* / Q000378:metabolism; D013450:Sulfones / Q000494:pharmacology; D014664:Vasodilation / Q000187:drug effects*
chemical_list: D002147:Calmodulin; D006146:Guanidines; D017923:Sodium-Hydrogen Exchangers; D013450:Sulfones; D009569:Nitric Oxide; C039465:5-dimethylamiloride; D000584:Amiloride; C093373:cariporide; D052250:Nitric Oxide Synthase Type III; D002118:Calcium; D019331:NG-Nitroarginine Methyl Ester