Dynamics of Na⁺,K⁺,2Cl⁻ cotransporter and Na⁺,K⁺‐ATPase expression in the branchial epithelium of brown trout (Salmo trutta) and atlantic salmon (Salmo salar)

Abstract

The dynamics of branchial Na(+),K(+),2Cl(-) cotransporter (NKCC) and Na(+),K(+)-ATPase (NKA) expression were investigated in brown trout and Atlantic salmon during salinity shifts and the parr-smolt transformation, respectively. In the brown trout, Western blotting revealed that NKCC and NKA abundance increased gradually and in parallel (30- and ten-fold, respectively) after transfer to seawater (SW). The NKA hydrolytic activity increased ten-fold after SW-transfer. Following back-transfer to fresh water (FW), the levels of both proteins and NKA activity decreased. The NKCC immunostaining in the gill of SW-acclimated trout was strong, and mainly localized in large cells in the filament and around the bases of the lamellae. In FW-acclimated trout, immunostaining was less intense and more diffuse. Partial cDNAs of the secretory NKCC1 isoform were cloned and sequenced from both brown trout and Atlantic salmon gills. Two differently sized transcripts were detected by Northern blotting in the gill but not in other osmoregulatory tissues (kidney, pyloric caeca, intestine). The abundance in the gill of these transcripts and of the associated NKCC protein increased four- and 30-fold, respectively, during parr-smolt transformation. The abundance of NKA alpha-subunit protein also increased in the gill during parr-smolt transformation though to a lesser extent than enzymatic activity (2.5- and eight-fold, respectively). In separate series of in vitro experiments, cortisol directly stimulated the expression of NKCC mRNA in gill tissue of both salmonids. The study demonstrates the coordinated regulation of NKCC and NKA proteins in the gill during salinity shifts and parr-smolt transformation of salmonids.

Cortisol regulation of ion transporter mRNA in Atlantic salmon gill and the effect of salinity on the signaling pathway

“…Consistent with the SW-adaptive role of NKCC (reviewed by McCormick 2001, Tipsmark et al 2002, cortisol increased NKCC mRNA levels but only in gills from SW-acclimated salmon. Previously, cortisol stimulated NKCC mRNA in FW gill in vitro (Tipsmark et al 2002) and NKCC protein level in vivo (Pelis & McCormick 2001).…”

“…Previously, cortisol stimulated NKCC mRNA in FW gill in vitro (Tipsmark et al 2002) and NKCC protein level in vivo (Pelis & McCormick 2001). A reason for the disparity in response to cortisol in the FW gill may be found in seasonal variation of sensitivity of the gill, since post-smolt salmon were used in this study whereas Tipsmark et al (2002) Scott et al (2005), where neither RU486 nor spironolactone implants affected the suppression of NKCC mRNA levels in BW-to FW-transferred killifish (Scott et al 2005).…”

“…Cortisol stimulated both transcripts in gills from both salinities thus agreeing with its dual role in osmoregulation (reviewed by McCormick 2001). Cortisol has previously been shown to increase overall Na (Seidelin et al 1999) and a-subunit mRNA (Tipsmark et al 2002) levels in the salmonid gill, but this is the first study to distinguish cortisol effects on the distinct Na C , K C -ATPase a1 isoforms and to give evidence for the involvement of both GR and MR. Curiously, the signaling pathway is opposite at the two salinities.…”

Involvement of redox- and phosphorylation-dependent pathways in osmotic adaptation in sperm cells of euryhaline tilapia

“…This adaptation involves modulation of ATPase and ion transporter activity, and changes in structural proteins (Evans, 2002). The adaptation response is based on the turnover of gill cilia and altered gill cell differentiation, which occur as a result of altered transcription (Tipsmark et al, 2002;Fiol and Kultz, 2005;Fiol et al, 2006). The architecture of the sperm flagellum is similar to that of the cilium, and the motility apparatuses of the flagellum and the cilium are structurally identical (Gibbons, 1981;Inaba, 2003).…”

Effects of cortisol and salinity acclimation on Na⁺/K⁺/2Cl^–- cotransporter gene expression and Na⁺, K⁺-ATPase activity in the gill of Persian sturgeon, <i>Acipenser persicus</i>, fry

“…Recently, duplicate isoforms have been reported for NKCC1 (NKCC1a and NKCC1b) in European eel and also two NKCC2 homologues have been isolated from Mozambique tilapia (Hiroi et al, 2005). Gill NKCC protein abundance was found to increase in European eels and sea bass (Lorin-Nebel, 2006) and also in salmonids during smoltification (Tipsmark et al 2002;Hiroi and McCormick, 2007). NKCC1 is the most widely distributed isoform whereas NKCC2 appears to be expressed in the kidney (Lytle et al, 1995;Bachmann et al, 1999;Lorin-Nebel et al, 2006).…”