Oxidative stress plays a permissive role in α2-adrenoceptor-mediated events in immortalized SHR proximal tubular epithelial cells
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The present study evaluated the role of oxidative stress on α2-adrenoceptor-mediated events (Cl−/HCO 3 − exchanger activity and cAMP accumulation) in immortalized renal proximal tubular epithelial (PTE) cells from the spontaneously hypertensive rat (SHR) and its normotensive control (Wistar Kyoto rat; WKY). The exposure of cells to α2-adrenoceptor agonist UK 14,304 reduced Cl−/HCO 3 − exchanger activity with EC50 of 2.0 μM in SHR PTE cells, whereas in WKY PTE cells no effects were observed. These effects were abolished by yohimbine, an α2-adrenoceptor antagonist, but insensitive to prazosin. Both forskolin and dibutyryl cAMP stimulated Cl−/HCO 3 − exchanger activity in WKY and SHR PTE cells, which was prevented by the PKA inhibitor H-89. Forskolin increased cAMP levels in both WKY and SHR PTE cells to a similar extent, but UK 14,304 significantly reduced the forskolin-induced increase in cAMP levels in only SHR PTE cells. Immunoblotting showed that expression of α2B-adrenoceptors was 12-times greater in SHR PTE cells than in WKY PTE cells. SHR PTE cells have increased levels of H2O2 and overexpress type 2 NADPH oxidase (NOX2) and p22phox compared with WKY cells. In SHR PTE cells, the NADPH oxidase inhibitor apocynin reduced their increased ability to generate H2O2 and abolished the inhibitory effects of UK 14,304 on Cl−/HCO 3 − exchanger activity and cAMP accumulation. It is concluded that differences between WKY and SHR PTE cells on their sensitivity to α2-adrenoceptor agonists correlate with the expression of α2B-adrenoceptors. The increased generation of H2O2 amplifies the response downstream to α2-adrenoceptor activation in SHR PTE cells.
KeywordsCl−/HCO3− exchanger Adenylyl cyclase α2-Adrenoceptor H2O2 Hypertension SHR WKY
This study is supported by Fundação para a Ciência e a Tecnologia, POCI, FEDER and Programa Comunitário de Apoio (POCI/SAU-FCF/59207/2004).
- 5.Rossier BC, Palmer LG (1992) Mechanisms of aldosterone action on sodium and potassium transport. In: Seldin DW (ed) The kidney, physiology and pathophysiology. Raven Press Publishers, New York, pp 1373–1409Google Scholar
- 7.Aronson PS, Giebisch G (1997) Mechanisms of chloride transport in the proximal tubule. Am J Physiol Renal Physiol 273:F179-F192Google Scholar
- 15.Hara C, Satoh H, Usui T, Kunimi M, Noiri E, Tsukamoto K, Taniguchi S, Uwatoko S, Goto A, Racusen LC, Inatomi J, Endou H, Fujita T, Seki G (2000) Intracellular pH regulatory mechanism in a human renal proximal cell line (HKC-8): evidence for Na+/H+ exchanger, CI−/HCO3− exchanger and Na+–HCO3− cotransporter. Pflugers Arch 440:713–20PubMedCrossRefGoogle Scholar
- 20.Minuz P, Patrignani P, Gaino S, Degan M, Menapace L, Tommasoli R, Seta F, Capone ML, Tacconelli S, Palatresi S, Bencini C, Del Vecchio C, Mansueto G, Arosio E, Santonastaso CL, Lechi A, Morganti A, Patrono C (2002) Increased oxidative stress and platelet activation in patients with hypertension and renovascular disease. Circulation 106:2800–2805PubMedCrossRefGoogle Scholar
- 29.Fraga S, Luo Y, Jose P, Zandi-Nejad K, Mount DB, Soares-da-Silva P (2006) Dopamine D1-like receptor-mediated inhibition of Cl/HCO3− exchanger activity in rat intestinal epithelial IEC-6 cells is regulated by G protein-coupled receptor kinase 6 (GRK 6). Cell Physiol Biochem 18:347–360PubMedCrossRefGoogle Scholar
- 38.Umemura S, Marver D, Smyth DD, Pettinger WA (1985) Alpha2-adrenoceptors and cellular cAMP levels in single nephron segments from the rat. Am J Physiol Renal Fluid Electrolyte Physiol 249:F28–F33Google Scholar