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First published online April 8, 2004
Journal of Experimental Biology 207, 1665-1674 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00925

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Cadmium induces both pyruvate kinase and Na⁺/H⁺ exchanger activity through protein kinase C mediated signal transduction, in isolated digestive gland cells of Mytilus galloprovincialis (L.)

Stefanos Dailianis and Martha Kaloyianni^*

Laboratory of Animal Physiology, Zoology Department, School of Biology, Faculty of Science, Aristotle University of Thessaloniki 54124, Greece

^* Author for correspondence (e-mail: Kaloyian{at}bio.auth.gr)

Received for publication 5 February 2004.

The present study investigates the transduction pathway mediated by cadmium in isolated digestive gland cells of mussel Mytilus galloprovincialis. The effects of cadmium treatment on a key glycolytic enzyme, pyruvate kinase (PK), and on Na⁺/H⁺ exchanger activity were examined. Cadmium (50 µmol l^–1) caused a significant elevation of intracellular pH (pHi) and a rise (176%) of Na influx relative to control values. The amiloride analogue, EIPA (20 nmol l^–1), a Na⁺/H⁺ exchanger blocker, together with cadmium, significantly reduced the effect of treatment by cadmium alone on both Na⁺ influx and pHi. In addition, PK activity was significantly increased after treatment with cadmium. PK activity was inhibited after treatment of cells with amiloride or EIPA together with cadmium. Moreover, phorbol-ester (PMA), a potent activator of protein kinase C (PKC), caused a significant rise in both pHi and PK activity, while staurosporine or calphostin C reversed both events. Adrenaline, isoprenaline and phenylephrine alone or together with cadmium also significantly increased the pHi and PK activity of isolated digestive gland cells. The latter effectors in combination with cadmium showed a synergistic effect on pHi and PK. These responses seem to be blocked by propranolol, metoprolol and prazosin. Our findings suggest a hormone-like effect of cadmium on digestive gland cells. The signal transduction pathway induced by cadmium involves the stimulation of PK, PKC and Na⁺/H⁺ exchanger in isolated digestive gland cells of Mytilus galloprovincialis.

Key words: mussel, Mytilus galloprovincialis, digestive gland, Na⁺/H⁺ exchanger, cadmium, pyruvate kinase, signal transduction