A Contribution to the Understanding of Osmoregulation in Two Tooth-Carps Occupying Different Osmotic Niches
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RESEARCH PAPER
A Contribution to the Understanding of Osmoregulation in Two ToothCarps Occupying Different Osmotic Niches Atefeh Zarei1 • Mina Motamedi1
•
Sara Soltanian1 • Azad Teimori1
Received: 17 July 2020 / Accepted: 31 August 2020 Ó Shiraz University 2020
Abstract The great ecological tolerance of aphaniid tooth-carps (Aphaniidae) suggests that the genetic-based adaptation to divergent osmoregulatory environments may be an important driver of the aphaniid fish diversity. This study was conducted to assess gill mRNA expression levels of two osmoregulatory genes, i.e., the CLC-3 and the Na?/K?-ATPase in two tooth-carps inhabiting the freshwater (FW) spring and salty water (SW) river. The expression pattern of genes was examined by quantitative real-time PCR. The number of ionocytes in the gill tissues was counted and compared using histological sections. The expression of CLC-3 in the FW fishes was 3.4 fold higher than that in the SW specimens, which highlighted the role of CLC-3 as a hyposmotically activated chloride channel. The expression of Na?/K?-ATPase was increased by 5.6 fold in the SW fishes. This upregulation in the SW fishes leads to the excretion of excess ions and maintains the homeostasis. The histological sections demonstrated that the ionocytes were distributed in the interlamellar region of the gill filament and that the average number of ionocytes was more in the SW fishes. This is probably an ecophysiological response to the saline condition of the habitat. The results of this study revealed that the examined osmogenes likely play an essential role in the adaptive responses of the studied killifishes to the variable osmotic conditions. Keywords Habitat ecology Aphaniops hormuzensis Aphanius sophiae Na?/K?-ATPase Ionocytes RT-qPCR
1 Introduction Osmoregulation and ion balance in teleost fishes are mainly achieved by the transportation of relevant ions (i.e., Na? and Cl–) through epithelial transporter systems across the gill (Marshall 2002; Hiroi et al. 2008; Evans et al. 2005; Hwang and Lee 2007; Evans 2008). Several types of cells consisting of the mucosal, the epithelial, and the specialized mitochondria-rich cells so-called ionocytes exist in the gill tissue of fishes, which are responsible for transepithelial ion transport. The ionocytes are the main localization sites for transporter enzyme, i.e., Na?/K?-ATPase. This enzyme acts as a cell marker to differentiate the chloride cells from the other cells. The Na?/K?-ATPase gene is a plasma membrane protein that helps in the maintenance of & Mina Motamedi [email protected] 1
Department of Biology, Faculty of Sciences, Shahid Bahonar University of Kerman, Kerman 76169-14111, Iran
electrochemical gradients of sodium and potassium ions across the plasma membrane and guarantees a constant osmolarity for the cells and blood plasma (Mobasheri et al. 2000). In killifish Fundulus heteroclitus, the Na?/K?-ATPase display salinity-dependent regulation when the fish is exposed to differen
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