Ionic and Amino Acid Regulation in Hard Clam (Meretrix lusoria) in Response to Salinity Challenges

Abstract

Most marine mollusks are osmoconformers, in that, their body fluid osmolality changes in the direction of the change in environmental salinity. Marine mollusks exhibit a number of osmoregulatory mechanisms to cope with either hypo- or hyperosmotic stress. The effects of changes in salinity on the osmoregulatory mechanisms of the hard clam (Meretrix lusoria, an economically important species of marine bivalve for Taiwan) have not been determined. In this study, we examined the effect of exposure to hypo (10‰)- and hyper (35‰)-osmotic salinity on hard clams raised at their natural salinity (20‰). The osmolality, [Na+], and [Cl−] of the hard clam hemolymph were changed in the same direction as the surrounding salinity. Further, the contents of total free amino acids including taurine in the gills and mantles were significantly upregulated in hard clam with increasing salinity. The gill Na+, K+-ATPase (NKA) activity, the important enzyme regulating cellular inorganic ions, was not affected by the changed salinity. Mantle NKA activity, however, was stimulated in the 35‰ SW treatment. The taurine transporter (TAUT) is related to the regulation of intracellular contents of taurine, the dominant osmolyte. Herein, a TAUT gene of hard clam was cloned and a TAUT antibody was derived for the immunoblotting. The TAUT mRNA expression of the mantle in hard clam was significantly stimulated in 35‰ SW, but protein expression was not modulated by the changed salinity. In gills of the hard clam with 10‰ SW, both TAUT mRNA and protein expressions were significantly stimulated, and it may reflect a feedback regulation from the decreased gills taurine content under long-term hypoosmotic acclimation. These findings suggest that TAUT expression is regulated differently in gills and mantles following exposure to alterations in environmental salinity. Taken together, this study used the physiological, biochemical and molecular approaches to simultaneously explore the osmoregulation in tissues of hard clam and may further help to understand the osmoregulation in bivalves.

Dilution of Seawater Affects the Ca2 + Transport in the Outer Mantle Epithelium of Crassostrea gigas

“…Bivalves are osmoconformers, with hemolymph osmolality following that of the environment (McFarland et al, 2013;Lin et al, 2016). When faced with hypo-osmotic conditions, epithelia tighten up to decrease the leakage of water into the tissues (Shumway, 1977b;Fuhrmann et al, 2018).…”

“…Reduction in environmental salinity has been shown to decrease the mantle NKA activity in multiple bivalve species such as Meretrix lusoria and M. galloprovincialis as well as in the abalone Haliotis discus hannai (Borgatti et al, 2003;Lin et al, 2016;Jia and Liu, 2018). However, in some species hypoosmotic conditions did not affect the NKA mRNA expression in the mantle (Paganini et al, 2010), gills (Lin et al, 2016) or whole body (Willmer, 1978;Peng et al, 2019) and in other cases increased it. Interestingly, when either up-or down-regulated, the need to maintain an electrochemical gradient across the cell membrane is suggested to explain the observed changes in NKA expression.…”

Time‐course changes in the regulation of ions and amino acids in the hard clam Meretrix lusoria upon lower salinity challenge

“…Accordingly, it is imperative that the hard clam is able adjust the cell volume of tissues when exposed to salinity stress. In this regard, only the physiological responses of hard clams under long-term adaptation to lower salinity environments have been examined to date (Lin et al, 2016).…”

Integrated transcriptomic and functional immunological approach for assessing the invasiveness of bivalve alien species

“…It seems clear that osmoregulatory and metabolic processes are enriched in X. securis , to the detriment of immune capabilities. It is likely that the daily variations in salinity in the inner part of the Ría de Vigo induce a high physiological stress for this species, as can be suggested by the high expression of ion and amino acid transporters, usually modulated during a decrease in water salinity 55,56 . In particular, the taurine concentration is one of the major contributors to the acclimation to salinity changes in Crassostrea gigas 57 and Mytilus galloprovincialis 58 .…”