Dynamic changes in nitric oxide synthase expression are involved in seawater acclimation of rainbow troutOncorhynchus mykiss

Abstract

Recent research has shown that nitric oxide (NO) produced by nitric oxide synthases (NOS) is an inhibitor of ion transporter activity and a modulator of epithelial ion transport in fish, but little is known on changes in the NOS/NO system during osmotic stress. We hypothesized that the NOS/NO system responds to salinity changes as an integrated part of the acclimation process. Expression and localization of nos1/Nos1 and nos2/Nos2 were investigated in gill, kidney, and intestine of freshwater (FW)- and seawater (SW)-transferred trout using quantitative PCR, Western blotting, and immunohistochemistry, along with expressional changes of major ion transporters in the gill. The classical branchial ion transporters showed expected expressional changes upon SW transfer, there among a rapid decrease in Slc26a6 mRNA, coding a branchial Cl/[Formula: see text] exchanger. There was a major downregulation of nos1/ nos2/Nos2 expression in the gill during SW acclimation. A significant decrease in plasma nitrite supported an overall decreased Nos activity and NO production. In the middle intestine, Nos1 was upregulated during SW acclimation, whereas no changes in nos/Nos expression were observed in the posterior intestine and the kidney. Nos1 was localized along the longitudinal axis of the gill filament, beneath smooth muscle fibers of the intestine wall and in blood vessel walls of the kidney. Nos2 was localized within the epithelium adjacent to the gill filament axis and in hematopoietic tissues of the kidney. We conclude that downregulation of branchial NOS is integrated to the SW acclimation process likely to avoid the inhibitory effects of NO on active ion extrusion.

Dietary Feeding Lycopene, Citric Acid, and Chlorella Alleviated the Neurotoxicity of Polyethylene Microplastics in African Catfish (Clarias gariepinus)

“…Inhibition of NO synthase can lead to decreased locomotor activity (Motahari et al, 2016). The NO system of fish responds to many environmental stressors, such as: tributyltin (Zhang et al, 2008;Li, et al, 2015), hyperammonia (Choudhury and Saha 2012b;Kumari et al, 2019), temperature elevation (Jørgensen et al, 2014), desiccation stress (Choudhury and Saha, 2012a;Garofalo et al, 2015), waterborne cadmium (Zheng et al, 2016), hyperosmotic stress (Gerber et al, 2018), and hypoxia/anoxia (Jensen et al, 2015;Hansen et al, 2016).…”

Nitric oxide synthase (NOS) inhibitor L‐NAME activates inducible NOS/NO system and drives multidimensional regulation of Na+/K+‐ATPase in ionocyte epithelia of immersion‐stressed air‐breathing fish (Anabas testudineus Bloch)

“…NO has been implicated in the modulation of Na + homeostasis and hypoxia tolerance in mammals and gill‐breathing fishes (Althanus, 2012; Ebbsson et al, 2005; Gerber et al, 2018; Malyshev & Manukhina, 1998). However, its role in NKA‐driven epithelial Na + transport is uncertain in air‐breathing fishes particularly in obligate air‐breathing fish like Anabas which shows resistance to acute hypoxemia when kept under forced submergence because of its dependence on atmospheric oxygen.…”

“…The NOS/NO system of fish responds to many environmental stressors such as hyperammonia (Choudhury & Saha, 2012a), temperature elevation (Jorgensen et al, 2014), desiccation stress (Choudhury & Saha, 2012b; Garofalo et al, 2015), hyperosmotic stress (Gerber et al, 2018) and hypoxia/anoxia (Imbrogno et al, 2014; Jensen et al, 2015; Sandvik et al, 2012; Hansen et al, 2016). Similarly, a role for NO in stress acclimation has been reported in fishes (Fago & Jensen, 2015; Hasan et al, 2020).…”

Seawater acclimation affects cardiac output and adrenergic control of blood pressure in rainbow trout (Oncorhynchus mykiss)—implications for salinity variations now and in the future

“…In mammals, intestinal hyperosmolarity, as would be expected with SW drinking in fish, have both direct vasodilatory effects on the gastrointestinal resistance vasculature, as well as indirect vasodilatory effects by stimulating nitric oxide production ( Bohlen, 1998 ; Levine et al , 1978 ; Steenbergen and Bohlen, 1993 ; Zani and Bohlen, 2005 ). Interestingly, an increased activity of neuronal nitric oxide synthase was found in the anterior intestine of rainbow trout after 7 days of exposure to SW (25 ppt; Gerber et al , 2018 ). This indicates a role of nitric oxide in SW-acclimation and as a possible mediator of gastrointestinal vasodilation.…”