Efeitos celulares do óxido nítrico em aorta de ratos hipertensos renais

Abstract

Listen

Translate article

Relaxation induced by nitric oxide (NO) donors is impaired in renal hypertensive two kidney-one clip (2K-1C) rat aortas. It has been proposed that caveolae are important in signal transduction and Ca homeostasis. Therefore, in the present study we investigate the integrity of caveolae in vascular smooth muscle cells (VSMCs), as well as their influence on the effects produced by NO released from both the new NO donor [Ru(NH.NHq) (terpy)NO ] (TERPY) and sodium nitroprusside (SNP) on 2K-1C rat aorta. The potency of both TERPY and SNP was lower in the 2K-1C aorta that in the normotensive aorta [two kidney (2K)], whereas the maximal relaxant effect (ME) was similar in both 2K-1C and 2K aortas. In the 2K aorta, methyl-cyclodextrin (CD) reduced both the potency of TERPY and SNP, and their ME compared with the control, but it had no effect on the potency and ME of these NO donors in 2K-1C aortas. The decrease in cytosolic Ca concentration ([Ca ]c) induced by TERPY was larger in 2K than in 2K-1C cells, and this effect was inhibited by CD in 2K cells only. Aortic VSMCs from 2K rats presented a larger number of caveolae than those from 2K-1C rats. Treatment with CD reduced the number of caveolae in both 2K and 2K-1C aortic VSMCs. Our results support the idea that caveolae play a critical role in the relaxant effect and in the decrease in [Ca ]c induced by NO, and they could be responsible for impaired aorta relaxation by NO in renal hypertensive rats. Caveolae are flask-shaped invaginations of the plasma membrane that are abundant in endothelial cells and vascular smooth muscle cells (VSMCs) (Voldstedlund et al., 2001). They are rich in cholesterol, glycosphingolipids, and the structural protein caveolin. Cholesterol is a very important component of caveolae, and it appears to be crucial to the maintenance of the structural integrity of this vesicular complex, because caveolae disappear in cells that are depleted of cholesterol. Previous studies have shown that cell exposure to sterol-binding agents such as methyl-cyclodextrin removes cholesterol from the plasmalemma. This causes caveolae disassembly (Linder et al., 2005), whereas the general morphology of the tissue is preserved. It has been proposed that caveolae are important in signal transduction. Diverse functional roles have been ascribed to them, including regulation of macromolecular transport, cell volume regulation, and Ca homeostasis (Taggart, 2001). Voltage-gated Na channels have been reported to be localized in cardiac myocyte caveolae (Yarbrough et al., 2002), and -subunits of L-type Ca channels can be found in caveolinenriched membranes in the smooth muscle (Darby et al., 2000). In addition, caveolin expression seems to enhance or to be required for the swelling-induced Cl channel function (Okada, 1999). Na /K -ATPase pump and Na /Ca exchange (Moore et al., 1993) are also found in caveolae. Furthermore, in many smooth muscles, caveolae are often in close proximity to the underlying network of the peripheral sarcoplasmic reticulum, commonly separated by distances as little as 10 to 40 nm (Nixon et al., 1994). Therefore, the fact that caveolae are located adjacent to the sarcoplasmic reticulum, close to channels, pumps, and exchangers important for Ca mobilization and transport, supports the notion that caveolae may influence Ca signaling. This work was supported by Fundacao de Amparo a Pesquisa do Estado de Sao Paulo and Conselho Nacional de Desenvolvimento Cientifico e Tecnologico. Article, publication date, and citation information can be found at http://jpet.aspetjournals.org. doi:10.1124/jpet.107.127241. ABBREVIATIONS: VSMC, vascular smooth muscle cell; NO, nitric oxide; TERPY, [Ru(NH.NHq)(terpy)NO ] ; SNP, sodium nitroprusside; 2K-1C, two kidney-one clip or renal hypertensive; 2K, two kidney or normotensive; PSS, physiological saline solution; CD, methyl-cyclodextrin; ME, maximal relaxant effect; YC-1, 3-(5 -hydroxymethyl-2 -furyl)-1-benzyl indazole. 0022-3565/07/3233-831–837$20.00 THE JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS Vol. 323, No. 3 Copyright © 2007 by The American Society for Pharmacology and Experimental Therapeutics 127241/3273599 JPET 323:831–837, 2007 Printed in U.S.A.