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First published online October 5, 2006
Journal of Experimental Biology 209, 4040-4050 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02462

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Plasticity of osmoregulatory function in the killifish intestine: drinking rates, salt and water transport, and gene expression after freshwater transfer

Graham R. Scott^1,*, Patricia M. Schulte¹ and Chris M. Wood²

¹ Department of Zoology, University of British Columbia, Vancouver BC, V6T 1Z4, Canada
² Department of Biology, McMaster University, Hamilton ON, L8S 4K1, Canada

^* Author for correspondence (e-mail: scott{at}zoology.ubc.ca)

Accepted 31 July 2006

We have explored intestinal function in the euryhaline killifish Fundulus heteroclitus after transfer from brackish water (10% seawater) to fresh water. Plasma Na⁺ and Cl^– concentrations fell at 12 h post-transfer, but recovered by 7 days. Drinking rate decreased substantially at 12 h (32% of control value) and remained suppressed after 3 and 7 days in fresh water (34 and 43%). By contrast, there was a transient increase in the capacity for water absorption measured across isolated intestines in vitro (3.3- and 2.6-fold at 12 h and 3 days), which returned to baseline after 7 days. These changes in water absorption could be entirely accounted for by changes in net ion flux: there was an extremely strong correlation (R²=0.960) between water absorption and the sum of net Na⁺ and net Cl^– fluxes (3.42±0.10 µl water µmol^–1 ion). However, enhanced ion transport across the intestine in fresh water would probably not increase water uptake in vivo, because the drinking rate was far less than the capacity for water absorption across the intestine. The increased intestinal ion absorption after freshwater transfer may instead serve to facilitate ion absorption from food when it is present in the gut. Modulation of net ion flux occurred without changes in mRNA levels of many ion transporters (Na⁺/K⁺-ATPase _1a, carbonic anhydrase 2, CFTR Cl^– channel, Na⁺/K⁺/2Cl^– cotransporter 2, and the signalling protein 14-3-3a), and before a measured increase in Na⁺/K⁺-ATPase activity at 3 days, suggesting that there is some other mechanism responsible for increasing ion transport. Interestingly, net Cl^– flux always exceeded net Na⁺ flux, possibly to help maintain Cl^– balance and/or facilitate bicarbonate excretion. Our results suggest that intestinal NaCl absorption from food is important during the period of greatest ionic disturbance after transfer to fresh water, and provide further insight into the mechanisms of euryhalinity in killifish.

Key words: Fundulus heteroclitus, intestine, water absorption, ion flux, drinking rate, cortisol, Na/K-ATPase, NKCC, CFTR, carbonic anhydrase, fish

This article has been cited by other articles:

				G. R. Scott, D. W. Baker, P. M. Schulte, and C. M. Wood Physiological and molecular mechanisms of osmoregulatory plasticity in killifish after seawater transfer J. Exp. Biol., August 1, 2008; 211(15): 2450 - 2459. [Abstract] [Full Text] [PDF]