AVT is involved in the regulation of ion transport in the intestine of the sea bream (Sparus aurata)

Abstract

The intestine of marine fish plays a crucial role in ion homeostasis by selective processing of ingested fluid. Although arginine vasotocin (AVT) is suggested to play a role in ion regulation in fish, its action in the intestine has not been demonstrated. Thus, the present study investigated in vitro the putative role of AVT in intestinal ion transport in the sea bream (Sparus aurata). A cDNA encoding part of an AVT receptor was isolated and phylogenetic analysis revealed it clustered with the V1a2-type receptor clade. V1a2 transcripts were expressed throughout the gastrointestinal tract, from esophagus to rectum, and were most abundant in the rectum regardless of long-term exposure to external salinities of 12, 35 or 55p.p.t. Basolateral addition of AVT (10(-6)M) to the anterior intestine and rectum of sea bream adapted to 12, 35 or 55p.p.t. mounted in Ussing chambers produced rapid salinity and region dependent responses in short circuit current (Isc), always in the absorptive direction. In addition, AVT stimulation of absorptive Isc conformed to a dose-response curve, with significant effects achieved at 10(-8)M, which corresponds to physiological values of plasma AVT for this species. The effect of AVT on intestinal Isc was insensitive to the CFTR selective inhibitor NPPB (200μM) applied apically, but was completely abolished in the presence of apical bumetanide (200μM). We propose a role for AVT in the regulation of ion absorption in the intestine of the sea bream mediated by an absorptive bumetanide-sensitive mechanism, likely NKCC2.

Vasotocinergic and isotocinergic systems in the gilthead sea bream (Sparus aurata): An osmoregulatory story

“…In addition, treatment of S. aurata with AVT and their subsequent transfer to different salinity conditions enhanced plasma cortisol level, gill and kidney Na + ,K + -ATPase activities and metabolism rate at plasma and tissue levels, reinforcing the idea of a hypoosmoregulatory role for AVT in this species (Sangiao-Alvarellos et al, 2006). Moreover, the effects of those hormones on several osmoregulatory epitheliums, such as gills, kidney or gastrointestinal tract, have been already reported in other species by their actions on ion absorption/secretion, urine production or glomerular filtration (Maetz et al, 1964;Motais and Maetz, 1967;Henderson and Wales, 1974;Amer and Brown, 1995;Martos-Sitcha et al, 2013).…”

Cortisol modulates vasotocinergic and isotocinergic pathways in the gilthead sea bream (Sparus aurata, Linnaeus 1758)

“…Several aspects of the vasotocinergic and isotocinergic systems have been previously characterised in the gilthead sea bream (S. aurata), and these systems have been putatively linked to several physiological processes, including osmoregulation Martos-Sitcha et al, 2013a;Martos-Sitcha et al, 2013b;Martos-Sitcha et al, 2014a), metabolism (Sangiao-Alvarellos et al, 2004;Sangiao-Alvarellos et al, 2006), and stress due to starvation and high stocking density (Mancera et al, 2008). However, relatively few studies have examined the link between stress pathway activation by cortisol and the vasotocinergic and isotocinergic systems.…”

“…In S. aurata, it has been demonstrated that AVT has regulatory effects on several molecular components of chloride cells, including the Na + /K + -ATPase pump (NKA), the cystic fibrosis transmembrane conductance regulator (CFTR) and the apical co-transporter Na + /K + /2Cl -(NKCC2), with the intracellular pathways of these receptors and ion transporters being shared (Martos-Sitcha et al, 2013a;Martos-Sitcha et al, 2014a). In fact, the development and proliferation of chloride cells, the increased NKA activity observed in several teleosts (McCormick, 1995;McCormick, 2012;Mancera et al, 2002;Laiz-Carrión et al, 2003) and the phenomenon of chloride secretion during episodes of chronic stress (Guibbolini et al, 1988;Martos-Sitcha et al, 2014a) support these conclusions.…”

“…Our research group has analysed various aspects of the vasotocinergic and isotocinergic systems of S. aurata in the context of osmoregulation, metabolism and multiple stressors Laiz-Carrión et al, 2002;Laiz-Carrión et al, 2005;Sangiao-Alvarellos et al, 2003b;Sangiao-Alvarellos et al, 2005;Sangiao-Alvarellos et al, 2006;Martos-Sitcha et al, 2013b). Recently, we cloned two distinct AVT receptors (AVTR V1a2 and V2) and one IT receptor (ITR), and we have characterised changes in the levels of these receptors during osmotic shifts (MartosSitcha et al, 2014a) and assessed their roles during intestinal ion transport (Martos-Sitcha et al, 2013a).…”

AVT and IT regulate ion transport across the opercular epithelium of killifish (Fundulus heteroclitus) and gilthead sea bream (Sparus aurata)

“…In the sea bream, AVT treatment enhanced gill Na + ,K + -ATPase activity after hyperosmotic challenge (SangiaoAlvarellos et al, 2006). Also, we have recently shown an enhancement in absorptive pathways mediated by AVT in the regulation of a bumetanide sensitive mechanism, likely NKCC co-transporter, in the intestine of sea bream (Martos-Sitcha et al, 2013).…”