In vivo and in vitro effects of high-K+ stress on branchial expression of ROMKa in seawater-acclimated Mozambique tilapia

Abstract

Recently, a teleost ortholog of renal outer medullary K(+) channel (ROMK) expressed in gill ionocytes (ROMKa) has emerged as a primary K(+)-excreting pathway in fish. However, the mechanisms by which ROMKa expression is regulated in response to perturbations of plasma K(+) levels are unknown. In this study, we aimed to identify potential links between the endocrine system and K(+) regulation in a euryhaline fish. We assessed time-course changes in multiple endocrine parameters, including plasma cortisol and gene expression of branchial glucocorticoid and mineralocorticoid receptors (GR1, GR2, and MR) and pituitary hormones, in seawater (SW)-acclimated Mozambique tilapia (Oreochromis mossambicus) exposed to high-K(+) (H-K) SW. Exposure to H-K SW elicited little effects on plasma cortisol or mRNA levels of GRs and pituitary hormones. Since plasma K(+) and branchial ROMKa expression was increased within 6h after H-K treatment in vivo, the effect of high K(+) was subsequently tested in a gill filament incubation experiment using media with differing K(+) concentrations. ROMKa mRNA levels were induced following incubation of filaments in H-K medium for 6h. The present study is the first to demonstrate that the expression of ROMKa in teleost ionocytes can respond to high K(+) conditions independent from systemic signaling.

Stable potassium isotopes (41K/39K) track transcellular and paracellular potassium transport in biological systems

“…K + loss is not well-understood but recent discoveries of apical ROMK channels indicate that transcellular secretion through MRCs is likely an important pathway ( Furukawa et al, 2012 ). Both stenohaline and euryhaline marine fish possess this capability but euryhaline marine fish have evolved the ability to adapt this machinery to a wide range of water salinities by adjusting expression of ROMK and tight junction claudins ( Furukawa et al, 2012 ; Kolosov et al, 2013 ; Furukawa et al, 2014 ; Furukawa et al, 2015 ).…”

Stable Potassium Isotopes (41K/39K) Track Transcellular and Paracellular Potassium Transport in Biological Systems

“…Specifically, Na + , K + and Cl - enter the MRC from the blood side via a basolateral Na + , K + , 2Cl - transporter (NKCC) driven by the inward directed Na + gradient created by basolateral Na,K-ATPase; Na + is recycled back to the blood via the Na,K-ATPase and secreted into seawater via “leaky” tight junction proteins (claudin 10; (36)); K + is either 1) secreted across the apical membrane into the seawater through ROMK channels or 2) recycled back to the blood via Kir channels while Cl - is secreted across the apical membrane via CFTR channels (5, 35). Both stenohaline and euryhaline marine teleosts possess this capability but euryhaline marine teleosts have evolved the ability to adapt this machinery to a wide range of water salinities by adjusting expression of NKCC, ROMK and tight junction claudins (5, 36–38).…”

“…K + loss is not well-understood but recent discoveries of apical ROMK channels indicate that transcellular secretion through MRCs is likely an important pathway (Furukawa et al, 2012). Both stenohaline and euryhaline marine fish possess this capability but euryhaline marine fish have evolved the ability to adapt this machinery to a wide range of water salinities by adjusting expression of ROMK and tight junction claudins (Furukawa et al, 2012; Furukawa et al, 2014; Furukawa et al, 2015; Kolosov et al, 2013).…”

Ecosystem and fish commercializing in a rich-minerals, low-salinity and semi-arid closed lake

“…Euryhaline shes can survive in environments with uctuated salinity through osmoregulation strategies to maintain a virtually persistent blood osmolality. Such species include Sparus aurata (Kir and Sunar, 2018), many mullets' species (Cardona 2001(Cardona , 2006; Lisboa et al, 2015; Loi et al, 2022), Lateolabrax maculatus (Tian et al, 2020), Oreochromis mossambicus (Furukawa et al, 2015), and Dicentrarchus labrax (Pickett et al, 2004). The patterns and mechanisms of osmotic and ionic regulation in euryhaline shes are well documented in adult sh (Mozanzadeh et al, 2021), juveniles (Kir and Sunar, 2018;Antony et al, 2020;Loi et al, 2022), early postembryonic stages, larval and post-larval stages (Thomas et al, 2021;Anand et al, 2023).…”