title: Na+/H+ exchanger inhibitor augments hyperosmolarity-induced vasoconstriction by enhancing actin polymerization.
abstract: Vascular smooth muscle cells (VSMCs) exhibit shrinkage-induced activation of Na(+)/H(+) exchanger isoform 1 (NHE-1) and Na(+), K(+), 2Cl(-) cotransporter (NKCC) under hyperosmotic conditions. To investigate the roles of these ion transporters in vascular smooth muscle force induced by hyperosmotic stress, we tested the effects of 5-(N, N-dimethyl)-amiloride (DMA; NHE inhibitor), cariporide (a selective NHE-1 inhibitor), and bumetanide (NKCC inhibitor) on the contractile response of rat aortic rings to hyperosmolar solutions. NHE inhibitors significantly augmented the maximum force response and contractile sensitivity to hyperosmolar sucrose, NaCl, and glucose in endothelium-denuded rings. Bumetanide elicited a comparatively modest increase in sensitivity. NHE inhibitors blocked the increase in intracellular pH and enhanced the cell volume decrease of cultured VSMCs after exposure to hyperosmolar sucrose. However, DMA had no effect on the increase in cytosolic free Ca(2+) concentration ([Ca(2+)]i) in rat VSMCs and on the increases in phosphorylation of myosin phosphatase target subunit 1 and myosin light chain (MLC) in aortic rings in response to hyperosmolar sucrose. Hyperosmolar sucrose-induced force was significantly attenuated by cytochalasin B in the presence or absence of DMA. Exposure to hyperosmolar sucrose increased the ratio of F- to G-actin; the ratio was further elevated by DMA. These results suggest that the potentiation of hyperosmotic shrinkage by NHE inhibition promotes actin polymerization in VSMCs and augments force production independent of changes in [Ca(2+)]i and MLC phosphorylation.
authors.affiliation: Laboratory of Cardiovascular Pharmacology, Department of Biopharmaceutical Sciences, Kobe Gakuin University, Minatojima 1-1-3, Chuo-ku, Kobe 6508586, Japan.
authors.forename: Tomoya
authors.initials: T
authors.lastname: Sasahara
authors.forename: Katsutoshi
authors.initials: K
authors.lastname: Yayama
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Tahara
authors.forename: Hirotaka
authors.initials: H
authors.lastname: Onoe
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Okamoto
mesh_terms: D000199:Actins / Q000378:metabolism; D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects* / Q000378:metabolism; D002034:Bumetanide / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D006146:Guanidines / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000378:metabolism; D018994:Myosin Light Chains / Q000187:drug effects / Q000378:metabolism; D009994:Osmolar Concentration; D010766:Phosphorylation / Q000187:drug effects; D058105:Polymerization / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors / Q000378:metabolism*; D028021:Sodium-Potassium-Chloride Symporters / Q000187:drug effects / Q000378:metabolism*; D013450:Sulfones / Q000494:pharmacology; D014661:Vasoconstriction / Q000187:drug effects*
chemical_list: D000199:Actins; D006146:Guanidines; D018994:Myosin Light Chains; D017923:Sodium-Hydrogen Exchangers; D028021:Sodium-Potassium-Chloride Symporters; D013450:Sulfones; C069139:growth factor-activatable Na-H exchanger NHE-1; D002034:Bumetanide; C039465:5-dimethylamiloride; D000584:Amiloride; C093373:cariporide; D002118:Calcium
keywords: 2′,7′-bis(carboxyethyl)-5,6-carboxyfluorescein tetraacetoxymethyl ester; 5-(N,N-dimethyl)-amiloride; BCECF-AM; Cell volume; Cytoskeleton; DMA; F-actin; G-actin; HBSS; Hanks' balanced salt solution; L-NAME; MLC; MYPT1; N(G)-nitro-L-arginine methyl ester; NHE; NKCC; NO; Na(+), K(+), 2Cl(−) cotransporter; Na(+)/H(+) exchanger; Na(+)/K(+)/2Cl(−) cotransporter; RVI; Smooth muscle; VSMCs; [Ca(2+)]i; cytosolic free calcium; filamentous-actin; globular-actin; intracellular pH; myosin light chain; myosin phosphatase target subunit 1; nitric oxide; p-MLC; p-MYPT1; pHi; phosphorylated MLC at Thr18 and Ser19; phosphorylated MYPT1 at Thr853; regulatory volume increase; vascular smooth muscle cells