Drinking and Water Handling in the Medaka Intestine: A Possible Role of Claudin-15 in Paracellular Absorption?

When euryhaline fish move between fresh water (FW) and seawater (SW), the intestine undergoes functional changes to handle imbibed SW. In Japanese medaka, the potential transcellular aquaporin-mediated conduits for water are paradoxically downregulated during SW acclimation, suggesting paracellular transport to be of principal importance in hyperosmotic conditions. In mammals, intestinal claudin-15 (CLDN15) forms paracellular channels for small cations and water, which may participate in water transport.

Prolactin controls Na,Cl cotransporter via Stat5 pathway in the teleost gill.

In some freshwater fish species, the control of gill Na, Cl cotransporter (Ncc2b) by prolactin appears to be instrumental to ionic homeostasis. This study was carried out to examine the signaling pathways involved in prolactin-mediated salt retention using gill explants from Japanese medaka (Oryzias latipes). Ovine prolactin induced a concentration-dependent stimulation of ncc2b with significant effects of 10, 100 and 1000 ng of hormone per mL media (2-6 fold).

Prolactin and cortisol regulate branchial claudin expression in Japanese medaka.

Several gill claudin (Cldn) tight junction proteins in Japanese medaka are regulated by salinity (cldn10 paralogs and cldn28b), while others are constitutively expressed (cldn27a, cldn28a and cldn30c). The role of the endocrine system in this regulation has yet to be understood. The in vitro effects of cortisol and prolactin on cldn expression in gill explant cultures were investigated in medaka.

Does Japanese medaka (Oryzias latipes) exhibit a gill Na(+)/K(+)-ATPase isoform switch during salinity change?

Some euryhaline teleosts exhibit a switch in gill Na(+)/K(+)-ATPase (Nka) α isoform when moving between fresh water (FW) and seawater (SW). The present study tested the hypothesis that a similar mechanism is present in Japanese medaka and whether salinity affects ouabain, Mg(2+), Na(+) and K(+) affinity of the gill enzyme. Phylogenetic analysis classified six separate medaka Nka α isoforms (α1a, α1b, α1c, α2, α3a and α3b).

Functional dynamics of claudin expression in Japanese medaka (Oryzias latipes): Response to environmental salinity.

Salinity regulation of 13 claudin paralogs was investigated in osmoregulatory organs of euryhaline Japanese medaka. They were identified by blast-search in the medaka genome database based on representation in osmoregulatory organs of other teleosts. Our hypothesis was that, because of their sequence similarities to mammalian orthologs previously characterized as barrier- and ion-selective channel-forming proteins, these paralogs would respond to salinity according to expected modulation of osmoregulatory function.

Transepithelial resistance and claudin expression in trout RTgill-W1 cell line: effects of osmoregulatory hormones.

In the present study, we examined the trout gill cell line RTgill-W1 as a possible tool for in vitro investigation of epithelial gill function in fish. After seeding in transwells, transepithelial resistance (TER) increased until reaching a plateau after 1-2 days (20-80Ω⋅cm(2)), which was then maintained for more than 6 days. Tetrabromocinnamic acid, a known stimulator of TER via casein kinase II inhibition, elevated TER in the cell line to 125% of control values after 2 and 6h.

Behavioural and transcriptional changes in the amphipod Echinogammarus marinus exposed to two antidepressants, fluoxetine and sertraline.

In the past decade, there have been increasing concerns over the effects of pharmaceutical compounds in the aquatic environment, however very little is known about the effects of antidepressants such as the selective serotonin re-uptake inhibitors (SSRIs). Many biological functions within invertebrates are under the control of serotonin, such as reproduction, metabolism, moulting and behaviour. The effects of serotonin and fluoxetine have recently been shown to alter the behaviour of the marine amphipod, Echinogammarus marinus (Leach, 1815).