The time course of seawater acclimation in Fundulus heteroclitus L.

SUMMARY 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 α1a,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.

Section: Contribution Of the Intestine To Water And Ion Homeostasis Insupporting

confidence: 88%

Section: Introductionmentioning

confidence: 99%

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

Scott

Schulte

Wood

2006

“…We employed killifish, Fundulus heteroclitus macrolepidotus (Walbaum 1792), which are ubiquitous along the Atlantic coast of Canada and the USA and are frequent inhabitants of intertidal marshes, creeks and estuaries. Killifish move with ease between salinities, adapt quickly (Marshall et al, 1999) and can survive direct transfer from freshwater to full-strength seawater (Jacob and Taylor, 1983;Zadunaisky et al, 1995). However, ionoregulation and osmoregulation are energetically expensive, requiring ATP-driven transporters to maintain homeostasis (reviewed by Boeuf and Payan, 2001), diverting energy away from growth and reproduction.…”

Section: Introductionmentioning

confidence: 99%

Diet influences salinity preference of an estuarine fish, the killifishFundulus heteroclitus

Bucking

Wood

Grosell

2012

SUMMARYUnderstanding the interplay among the external environment, physiology and adaptive behaviour is crucial for understanding how animals survive in their natural environments. The external environment can have wide ranging effects on the physiology of animals, while behaviour determines which environments are encountered. Here, we identified changes in the behavioural selection of external salinity in Fundulus heteroclitus, an estuarine teleost, as a consequence of digesting a meal. Fish that consumed high levels of dietary calcium exhibited a higher preferred salinity compared with unfed fish, an effect that was exaggerated by elevated dietary sodium chloride. The mean swimming speed (calculated as a proxy of activity level) was not affected by consuming a diet of any type. Constraining fish to water of 22p.p.t. salinity during the digestion of a meal did not alter the amount of calcium that was absorbed across the intestine. However, when denied the capacity to increase their surrounding salinity, the compromised ability to excrete calcium to the water resulted in significantly elevated plasma calcium levels, a potentially hazardous physiological consequence. This study is the first to show that fish behaviourally exploit their surroundings to enhance their ionoregulation during digestion, and to pinpoint the novel role of dietary calcium and sodium in shaping this behaviour. We conclude that in order to resolve physiological disturbances in ion balance created by digestion, fish actively sense and select the environment they inhabit. Ultimately, this may result in transient diet-dependent alteration of the ecological niches occupied by fishes, with broad implications for both physiology and ecology.

“…Remarkably, killifish can tolerate acute transfer from freshwater to seawater and from seawater to freshwater with only minor, transient alterations in blood plasma osmolarity and Na + concentration by rapidly controlling NaCl transport (Jacob and Taylor, 1983;Wood and Marshall, 1994;Marshall et al, 1999;Wood and Laurent, 2003). The key ion transporters and cells (chloride cells) that mediate NaCl secretion from teleost gills are well described, and have been reviewed extensively (Perry, 1997;Karnaky, 1998;Marshall, 2002;Hirose et al, 2003;Evans et al, 2005).…”

Section: Introductionmentioning

confidence: 99%

COX2 in a euryhaline teleost,Fundulus heteroclitus: primary sequence, distribution, localization, and potential function in gills during salinity acclimation

Choe

Havird

Rose

et al. 2006

SUMMARY In the kidneys of mammals, cyclooxygenase type 2 (COX2) is expressed in medullary interstitial cells, the macula densa and epithelial cells of the cortical thick ascending limb where it generates prostaglandins that regulate hormone secretion, inhibit ion transport, and support cell survival during salt loading and dehydration. In teleosts, the gills are in direct contact with an aquatic environment and are the dominant site of osmoregulation. During transfers between salinities, specialized cells in the gills (chloride cells) rapidly regulate NaCl secretion for systemic osmoregulation while they simultaneously are exposed to acute osmotic shock. This study was conducted to determine if COX2 is expressed in the gills, and if so, to evaluate its function in cellular and systemic osmoregulation. Degenerate primers, reverse transcription–PCR and rapid amplification of cDNA ends were used to deduce the complete cDNA sequence of a putative COX2 enzyme from the gills of the euryhaline killifish (Fundulus heteroclitus). The 2738 base pair cDNA includes a coding region for a 610 amino acid protein that is over 70%identical to mammalian COX2. A purified antibody generated against a conserved region of mouse COX2 labeled chloride cells, suggesting that the enzyme may control NaCl secretion as an autocrine agent. Real-time PCR was then used to demonstrate that mRNA expression of the COX2 homologue was threefold greater in gills from chronic seawater killifish than in gills from chronic freshwater killifish. Expression of Na+/K+/2Cl–cotransporter and the cystic fibrosis transmembrane conductance regulator were also greater in seawater, suggesting that chronic COX2 expression in the gills is regulated in parallel to the key ion transporters that mediate NaCl secretion. Real-time PCR was also used to demonstrate that acute transfer from seawater to freshwater and from freshwater to seawater led to rapid, transient inductions of COX2 expression. Together with previous physiological evidence,the present molecular and immunological data suggest that constitutive branchial COX2 expression is enhanced in seawater, where prostaglandins can regulate NaCl secretion in chloride cells. Our data also suggest that branchial COX2 expression may play a role in cell survival during acute osmotic shock.