Control mechanisms of amino acid‐mediated cell volume regulation in salinity‐stressed molluscs

Abstract

The mechanisms of cell volume regulation in molluscs have been examined in detail in only a few species. While generalizations must be made with some caution until additional species have been tested, the following mechanism has emerged. When stressed with a decreased external salinity the cells of osmoconforming bivalves swell for a period of time and then recover toward the original cell volume. The volume recovery is effected by an efflux of intracellular free amino acids which act as osmotic solute. While the drop in external osmolality initiates the efliux, the duration of the efflux (restoration of normal amino acid permeability) relies on the activity of a Ca2+ -Mg2+ requiring ATPase.In addition, cell volume regulation and the amino acid efflux are accompanied by an alteration in the number of membrane associated particles per unit of membrane area. While the relationship between the ATPase activity, membrane associated particles and amino acid permeability is not yet clear, there is good evidence that the mechanism of cell volume control resides with the cell membrane in these animals.

Genome and Transcriptome Analyses Provide Insight into the Euryhaline Adaptation Mechanism of Crassostrea gigas

“…To adapt to changes or fluctuations in the salinity of ambient seawater, osmo-conforming marine animals, including oysters, exhibited mechanisms that allow them to adjust the concentrations of intracellular osmolytes to regulate cell volume. Previous studies have shown that intracellular FAAs are the main contributors to the regulation of intracellular osmolality and cell volume in bivalves [11]. However, FAAs osmotic regulation molecular mechanism has been little studied to our knowledge.…”

“…In oyster, salt stress mainly induces an osmotic response. Many studies have revealed that intracellular free amino acids (FAAs) predominantly contribute to intracellular osmolality and to cell volume regulation in oysters [11]. The functions of FAAs as osmolytes have been reported by previous studies [16].…”

“…Facing salinity stress, osmoconforming oysters exhibit a number of functional mechanisms to prevent their internal medium from fluctuating widely. Their physiological reactions and tolerance to changes in salinities have been studied by numerous authors [5], [11], [12], [13], [14]. The salt stress responses have been shown to encompass several aspects, including reversible changes in protein and RNA synthesis, alteration of the patterns of multiple molecular forms of different enzymes, and regulation of ionic content and cell volume [15].…”

Dynamic changes in the accumulation of metabolites in brackish water clam Corbicula japonica associated with alternation of salinity

“…Although there are several data about the effects of the environmental stress on the clam metabolism, the adaptation to the salinity change has remained largely unknown (Liu et al, 2011;Zhang et al, 2011aZhang et al, ,2011bZhang et al, ,2011cWu et al, 2013). The bivalves change ion and intracellular free amino acid concentrations to maintain inorganic ion strength (Pierce and Amende, 1981;Pierce, 1982). For instance, Na + , Ca 2+ and Mg 2+ concentrations in the hemolymph of bivalves such as queen scallop Chlamys opercularis change depending on salinity, whereas alanine, proline, glycine and glycine betaine are accumulated in the gill of ribbed mussel Geukensia demissa at high salinity (Shumway, 1977;Bishop et al, 1994;Deaton, 2001).…”

Egg-Mass Gel of Melanochlamys diomedea (Bergh) Protects Embryos From Low Salinity

“…Although intracellular solutes were not studied in M. diomedea, many marine invertebrates regulate the levels of these substances, especially free amino acids and some inorganic ions, in order to minimize osmotic concentration differences between cellular and external spaces (Amende and Pierce, 1980;Bedford, 1971;Chamberlin and Strange, 1989;Clark, 1985;Florkin and Schoffeniels, 1969;Greenwalt and Bishop, 1980;Kasschau, 1975;Pierce and Amende, 1981;Silva and Wright, 1994). But regulation of intracellular solutes is not instantaneous (Amende and Pierce, 1980;Burton, 1991;Neufeld and Wright, 1996;Silva and Wright, 1994).…”