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First published online March 17, 2006
Journal of Experimental Biology 209, 1344-1354 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02134

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Extracellular pH changes activate the p38-MAPK signalling pathway in the amphibian heart

Konstantina Stathopoulou, Catherine Gaitanaki and Isidoros Beis^*

Department of Animal and Human Physiology, School of Biology, Faculty of Sciences, University of Athens, Panepistimioupolis, Athens 157 84, Greece

^* Author for correspondence (e-mail: ibeis{at}biol.uoa.gr)

Accepted 30 January 2006

We investigated the activation of the p38-MAPK signalling pathway during extracellular pH changes in the isolated perfused amphibian heart. Extracellular alkalosis (pH 8.5 or 9.5) maximally activated p38-MAPK within 2 min (4.17- and 3.20-fold, respectively) and this effect was reversible since the kinase phosphorylation levels decreased upon reperfusing the heart with normal Tris–Tyrode's buffer. Extracellular acidosis also activated p38-MAPK moderately, but persistently (1.65-fold, at 1 min and 1.91-fold, at 60 min). The alkalosis-induced p38-MAPK activation depended upon the Na⁺/H⁺ exchanger (NHE) and Na⁺/K⁺-ATPase, because it was abolished when the NHE inhibitors amiloride and HOE642 and the Na⁺/K⁺-ATPase inhibitor, ouabain, were used. Our studies also showed that extracellular alkalosis (pH 8.5) induced MAPKAPK2 phosphorylation (2.59-fold, 2 min) and HSP27 phosphorylation (5.33-fold, 2 min) in a p38-MAPK-dependent manner, as it was inhibited with 1 µmol l^–1 SB203580. Furthermore, immunohistochemical studies of the phosphorylated forms of p38-MAPK and HSP27 revealed that these proteins were localised in the perinuclear region and dispersedly in the cytoplasm of ventricular cells during alkalosis. Finally, alkalosis induced the increase of HSP70 protein levels (1.52-fold, 5 min), but independently of p38-MAPK activation. These data indicate that the p38-MAPK signalling pathway is activated by extracellular pH changes and in the case of alkalosis this activation may have a protective role.

Key words: alkalosis, acidosis, p38-MAPK, HSP27, amphibian heart, Rana ridibunda, signal transduction, cellular signalling

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