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First published online July 2, 2004
Journal of Experimental Biology 207, 2823-2833 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01103

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Temperature acclimation modifies Na⁺ current in fish cardiac myocytes

Jaakko Haverinen and Matti Vornanen^*

University of Joensuu, Department of Biology, PO Box 111, 80101 Joensuu, Finland

^* Author for correspondence (e-mail: matti.vornanen{at}joensuu.fi)

Accepted 20 May 2004

The present study was designed to test the hypothesis that temperature acclimation modifies sarcolemmal Na⁺ current (I_Na) of the fish cardiac myocytes differently depending on the animal's lifestyle in the cold. Two eurythermal fish species with different physiological strategies for surviving in the cold, a cold-dormant crucian carp (Carassius carassius L.) and a cold-active rainbow trout (Oncorhynchus mykiss), were used in acclimation experiments. The I_Na of carp and trout were also compared with I_Na of a cold stenothermal burbot (Lota lota). In accordance with the hypothesis, cold-acclimation decreased the density of I_Na in crucian carp and increased it in rainbow trout, suggesting depression of impulse conduction in cold-acclimated carp and positive compensation of impulse propagation in cold-acclimated trout. The steady-state activation curve of trout I_Na was shifted by 6 mV to more negative voltages by cold acclimation, which probably lowers the stimulus threshold for action potentials and further improves cardiac excitability in the cold. In burbot myocytes, the I_Na density was high and the position of the steady-state activation curve on the voltage axis was even more negative than in trout or carp myocytes, suggesting that the burbot I_Na is adapted to maintain high excitability and conductivity in the cold. The I_Na of the burbot heart differed from those of carp and trout in causing four times larger charge influx per excitation, which suggests that I_Na may also have a significant role in cardiac excitation–contraction coupling of the burbot heart. In summary, I_Na of fish cardiac myocytes shows thermal plasticity that is different in several respects in cold-dormant and cold-active species and thus has a physiologically meaningful role in supporting the variable life styles and habitat conditions of each species.

Key words: fish heart, thermal acclimation, sodium current, Carassius carassius, Oncorhynchus mykiss, Lota lota

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