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First published online January 27, 2004
Journal of Experimental Biology 207, 841-852 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00839

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Sodium and potassium currents of larval zebrafish muscle fibres

Steven D. Buckingham and Declan W. Ali^*

Department of Biological Sciences, University of Alberta, CW-405 Biological Sciences Building, Edmonton, Alberta, T6G 2E9, Canada

^* Author for correspondence (e-mail: declan.ali{at}ualberta.ca)

Accepted 15 December 1003

The steady-state and kinetic properties of Na⁺ and K⁺ currents of inner (white) and outer (red) muscles of zebrafish larvae 4–6 days post-fertilization (d.p.f.) are described. In inner muscle, the outward currents were half-activated at –1.0 mV and half-inactivated at –30.4 mV, and completely inactivated within 100 ms of depolarization. The inward currents of inner fibres were half-activated at –7.3 mV and half-inactivated at –74.5 mV and completely inactivated within 5 ms of depolarization. Inner muscle fibres were found to support action potentials, while no action potentials could be evoked in outer muscles. In inner muscle fibres, all tested levels of depolarizing current above a threshold value evoked only one action potential. However, spiking at frequencies of up to 200 cycles s^–1 was evoked by the injection of depolarizing pulses separated by short hyperpolarizing currents. We suggest that the properties of the inward sodium and outward potassium currents permit high frequency firing in response to a pulsatile depolarizing input of the kind expected in fast swimming, whilst safeguarding against tetany during a strong depolarization.

Key words: zebrafish, Danio rerio, muscle, sodium current, potassium current, action potential

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