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First published online January 17, 2007
Journal of Experimental Biology 210, 438-446 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.02680

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Cu²⁺ and acute thermal stress induce protective events via the p38-MAPK signalling pathway in the perfused Rana ridibunda heart

Catherine Gaitanaki, Maria Pliatska, Konstantina Stathopoulou 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 5 December 2006

In the present study, we investigated the induction of the p38-MAPK signalling pathway by copper, as exemplified by CuCl₂, in the isolated perfused heart of the amphibian Rana ridibunda. We found that p38-MAPK phosphorylation by CuCl₂ occurs in a dose-dependent manner, with maximum activation (8.73±1.43-fold relative to control values) attained by perfusion with 500 µmol l^–1 CuCl₂ for 15 min, while this activation sustained even after 60 min of reperfusion with normal bicarbonate buffer. CuCl₂ also induced the phosphorylation of the small heat shock protein 27 (Hsp27) in a p38-MAPK dependent manner, as revealed by experiments using the p38-MAPK inhibitor SB203580. p38-MAPK and Hsp27 phosphorylations were also strongly induced by hyperthermia (42°C), while the simultaneous use of hyperthermia and CuCl₂ had a synergistic effect on p38-MAPK activation. Furthermore, perfusions with the potent antioxidant L-ascorbic acid (100 µmol l^–1), the antioxidant enzymes catalase (CAT) (150 U ml^–1) or superoxide dismutase (SOD) (30 U ml^–1) in the presence of 500 µmol l^–1 CuCl₂ did not attenuate the CuCl₂-induced p38-MAPK activation, implying that at least the reactive oxygen species (ROS) scavenged by these agents are not implicated in this kinase activation. The p38-MAPK phosphorylation induced by the combined action of CuCl₂ and hyperthermia was partially inhibited by catalase, indicating that hyperthermia possibly activates the kinase through the production of H₂O₂. Caspase-3, an effector protease of apoptosis, remained inactive in hearts perfused at normal or hyperthermic conditions, in the absence or presence of 500 µmol l^–1 CuCl₂. All the above results suggest that, in the amphibian Rana ridibunda heart, p38-MAPK activation by copper has a possible protective role through the small Hsp27.

Key words: oxidative stress, thermal stress, copper, antioxidants, p38-MAPK, Hsp27, amphibian heart, Rana ridibunda, signal transduction

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