Differential expression of Na+, K+-ATPase α-1 isoforms during seawater acclimation in the amphidromous galaxiid fish Galaxias maculatus

Abstract

Inanga (Galaxias maculatus) is an amphidromous fish with a well-known capacity to withstand a wide range of environmental salinities. To investigate the molecular mechanisms facilitating acclimation of inanga to seawater, several isoforms of the Na(+), K(+)-ATPase ion transporter were identified. This included three α-1 (a, b and c), an α-2 and two α-3 (a and b) isoforms. Phylogenetic analysis showed that the inanga α-1a and α-1b formed a clade with the α-1a and α-1b isoforms of rainbow trout, while another clade contained the α-1c isoforms of these species. The expression of all the α-1 isoforms was modulated after seawater exposure (28‰). In gills, the expression of the α-1a isoform was progressively down-regulated after seawater exposure, while the expression of the α-1b isoform was up-regulated. The α-1c isoform behaved similarly to the α-1a, although changes were less dramatic. Physiological indicators of salinity acclimation matched the time frame of the changes observed at the molecular level. A 24-h osmotic shock period was highlighted by small increases in plasma osmolality, plasma Na(+) and a decrease in muscle tissue water content. Thereafter, these values returned close to their pre-exposure (freshwater) values. Na(+), K(+)-ATPase activity showed a decreasing trend over the first 72 h following seawater exposure, but activity increased after 240 h. Our results indicate that inanga is an excellent osmoregulator, an ability that is conferred by the rapid activation of physiological and molecular responses to salinity change.

Sublethal salinity stress contributes to habitat limitation in an endangered estuarine fish

“…In teleosts, a hallmark effector of osmoregulation in the gills is the modulation of NKA along with related cotransporters to effectively maintain osmotic and ionic balance (Evans et al 2005;Hwang and Lin 2013). Studies in a variety of fishes have documented increased NKA activity with osmotic stress (Marshall 2013) and NKA 'isoform switching', in which one isoform is upregulated at low salinities while another is downregulated and vice versa at increased salinities (Richards et al 2003;Bystriansky et al 2006;Urbina et al 2013). Additionally, delta smelt downregulated gene expression of multiple NKA subunits at high salinities, but we did not detect any reciprocal increases in the transcription of alternate isoforms.…”

“…; Urbina et al. ). Additionally, delta smelt downregulated gene expression of multiple NKA subunits at high salinities, but we did not detect any reciprocal increases in the transcription of alternate isoforms.…”

Adaptive genomic divergence under high gene flow between freshwater and brackish‐water ecotypes of prickly sculpin (Cottus asper) revealed by Pool‐Seq

“…ATPase is crucial for maintaining the ion balance and electrolyte homeostasis in different osmoregulatory epithelia (Evans et al 2005), with a plethora of studies supporting its adaptive function for ion uptake in freshwater in teleost fishes (e.g. Hohenlohe et al 2010;Shikano et al 2010;Norman et al 2011;Papakostas et al 2012;Kozak et al 2013;Urbina et al 2013;Whitehead et al 2013;DeFaveri & Meril€ a 2014;Sutherland et al 2014;Velotta et al 2014). Overall, ATPase isozymes appear to be evolutionarily highly conserved (e.g.…”

Physiological and biochemical strategies for withstanding emersion in two galaxiid fishes

“…Gill NKA activity was assessed using a modified microplate assay (McCormick, 1993), as previously described by Urbina et al (2013). NKA activity was considered the ouabain-sensitive component of total gill ATPase activity, per unit of protein in the supernatant.…”