Time‐Course Changes in the Expression of Na⁺,K⁺‐ATPase in Gills and Pyloric Caeca of Brown Trout (Salmo trutta) during Acclimation to Seawater

Abstract

Changes in protein and mRNA expression of Na(+),K(+)-ATPase in gills and pyloric caeca of brown trout were investigated on a detailed time course after transfer from freshwater to 25 ppt seawater (SW). A transient deflection in plasma osmolality and muscle water content lasting from 4 h until day 3 was followed by restoration of hydromineral balance from day 5 onward. Gills and pyloric caeca responded to SW transfer by increasing Na(+),K(+)-ATPase activity from days 5 and 3, respectively, onward. In both tissues, this response was preceded by an increase in alpha-subunit Na(+), K(+)-ATPase mRNA as early as 12 h posttransfer. The similarity of the response in these two organs suggests that they both play significant physiological roles in restoring hydromineral balance after abrupt increase in salinity. Further, SW transfer induced a slight, though significant, increase in primary gill filament Na(+), K(+)-ATPase immunoreactive (NKIR) cell abundance. This was paralleled by a marked (50%) decrease in secondary lamellar NKIR cell abundance after less than 1 d in SW. Thus, SW acclimation in brown trout is characterised by a lasting decrease in overall NKIR cell abundance in the gill. We propose that SW transfer stimulates Na(+),K(+)-ATPase enzymatic activity within individual chloride cells long before (<1 d) it becomes apparent in measurements of whole-gill homogenate enzymatic activity. This is supported by the early stabilisation (12 h) of hydromineral balance.

Reciprocal expression of gill Na+/K+-ATPaseα-subunit isoforms α1a and α1b during seawater acclimation of three salmonid fishes that vary in their salinity tolerance

“…In order to better understand what limits the seawater tolerance of different salmonid species (or individuals), it is important to understand the regulation of gill Na Following exposure to seawater, the level of Na + /K + -ATPase ␣1a mRNA is rapidly reduced in all three species examined. This decreased amount of isoform ␣1a is in contrast to many studies that report an increase in gill Na + /K + -ATPase mRNA expression during salinity acclimation of salmonid fishes (Madsen et al, 1995;D'Cotta et al, 2000;Seidelin et al, 2000;Singer et al, 2002;Tipsmark et al, 2002). However, those studies did not distinguish between individual isoforms of Na + /K + -ATPase, as they used probes designed for northern blot analysis that were created based on highly conserved regions of Na (Madsen et al, 1995;D'Cotta et al, 2000;Seidelin et al, 2000;Singer et al, 2002;Tipsmark et al, 2002) is probably due to a specific increase in ␣1b isoform expression.…”

“…This decreased amount of isoform ␣1a is in contrast to many studies that report an increase in gill Na + /K + -ATPase mRNA expression during salinity acclimation of salmonid fishes (Madsen et al, 1995;D'Cotta et al, 2000;Seidelin et al, 2000;Singer et al, 2002;Tipsmark et al, 2002). However, those studies did not distinguish between individual isoforms of Na + /K + -ATPase, as they used probes designed for northern blot analysis that were created based on highly conserved regions of Na (Madsen et al, 1995;D'Cotta et al, 2000;Seidelin et al, 2000;Singer et al, 2002;Tipsmark et al, 2002) is probably due to a specific increase in ␣1b isoform expression. This suggests ␣1b might be the specific Na J. S. Bystriansky and others mRNA was increased in each of the three species by the first sampling period (day·1 for Arctic char, 2 for rainbow trout, 4 for Atlantic salmon).…”

Na+/K+-ATPase α-isoform switching in gills of rainbow trout (Oncorhynchus mykiss) during salinity transfer

“…These increases in gill Na + /K + -ATPase activity are, in general, either preceded by or accompanied by increases in Na + /K + -ATPase α-subunit mRNA. Specifically, increases in Na + /K + -ATPase α-subunit mRNA during salinity transfer have been shown in Atlantic salmon Salmo salar (D'Cotta et al, 2000;Singer et al, 2002), brook trout Salmo trutta (Madsen et al, 1995;Seidelin et al, 2000), the European eel (Cutler et al, 1995a), and the European sea bass Dicentrarchus labrax (Jensen et al, 1998). Increases in Na + /K + -ATPase α1 and α3-subunit protein abundance also occur in tilapia gills following seawater transfer (Lee et al, 2003(Lee et al, , 1998.…”

Intestinal anion exchange in marine fish osmoregulation

“…The NKA activity is generally high in marine fish intestine, even when compared to the gill Hogstrand et al, 1999), and is higher in euryhaline fish acclimated to seawater than in freshwater acclimated individuals (Colin et al, 1985;Fuentes et al, 1997;Jampol and Epstein, 1970;Kelly et al, 1999;Madsen et al, 1994), illustrating the osmoregulatory importance of this enzyme. Furthermore, NKA gene M. Grosell expression is elevated in the intestine of euryhaline teleost fish following transfer from freshwater to seawater, demonstrating the significance of this enzyme for successful marine osmoregulation (Cutler et al, 2000;Jensen et al, 1998;Seidelin et al, 2000).…”