Cellular and subcellular distribution of metals in molluscs

Abstract

The cellular processes involved in metal metabolism in molluscs are reviewed, with emphasis on the contribution of microscopy (AMG, ARG, EPMA, and SIMS) to both basic research of metal cell biology and applied environmental research. In molluscs, metal uptake may occur by facilitated diffusion, active transport, or endocytosis, and can be enhanced by MT synthesis or formation of mineralized granules. In aquatic molluscs, gills constitute a key interface for dissolved metal uptake, where metals are bound to MT, incorporated into lysosomes, and released basally towards the blood plasma and circulating hemocytes. However, particulate metal uptake is mainly achieved via the digestive tract by endocytosis; further metals are transferred first to lysosomes and then to residual bodies, especially in the digestive cells of the digestive gland. Additionally, metals can be accumulated selectively in specific cell types. As ligands pools differ from cell to cell, different metals may be retained in different cell types. Class "a" metals are localized in cells with granules composed of carbonate, oxalate, phosphate, and sulfate (oxygen donors), whereas "b" metals are associated with those cell types rich in sulfur and nitrogen ligands (sulfur donors). In molluscs, oxygen donors occur in connective tissue calcium cells and basophilic cells, whereas sulfur donors are present in digestive cells, podocytes, nephrocytes, and rhogocytes. Hemocytes, which constitute the most relevant system for metal transport between tissues, move around the body and may penetrate tissues and remove metals from the inner medium to be accumulated in lysosomes as nondigested products. Rhogocytes also participate in metal mobilization, accumulation, and release. The assessment of metal levels in target cells of sentinel molluscs by microscopic techniques provides an early-warning measure, with promising applications as an exposure biomarker for environmental monitoring programs.

Effects of hypoxia in the gills of the Manila clam Ruditapes philippinarum using NMR-based metabolomics

“…1). The irregularity of epithelium and loss of interlamellar tissue of the gill filaments may have significant effects on respiration and , isoleucine; 2, alanine; 3, succinate; 4, betaine; 5, arginine; 6, glycine; 7, tyrosine; 8, phenylalanine; and 9, aspartate. food uptake, as previously reported (Marigómez et al, 2002;Au, 2004;Abdel-Nabi et al, 2007), although food clearance rates were not measured in the current study. In support of this, a previous study showed that repeated exposure to hypoxia reduces the clearance rate (Kozuki et al, 2013).…”

“…The gills and hepatopancreas of bivalve species are responsive and sensitive to environmental stressors (Marigómez et al, 2002;Au, 2004;Abdel-Nabi et al, 2007). In the present study, we observed that the gills of R. philippinarum exposed to hypoxia lost their structures (Fig.…”

Relative importance of direct and trophic uranium exposures in the crayfish Orconectes limosus: Implication for predicting uranium bioaccumulation and its associated toxicity

“…These are often used as indicators of freshwater metal pollution, because they tend to rapidly accumulate metals and radionuclides (uranium) exposure pathways. As prey for trophic exposure experiments, we selected the Asiatic clam, C. fluminea, which is well known for its high capacity for metal bioaccumulation [33][34][35][36].…”

Differences in metal sequestration between zebra mussels from clean and polluted field locations

“…With this, essential metals in excess of metabolic requirements and non-essential metals are detoxified and/or excreted (Rainbow, 2002;Campbell et al, 2005Campbell et al, , 2008. Excess of metals can be bound to the metal binding protein metallothionein (Vijver et al, 2004;Van Campenhout et al, 2008) and (subsequently) immobilized within granules (Marigómez et al, 2002). Metal-rich granules can be excreted via faeces or basal exocytosis towards haemocytes (Desouky, 2006).…”

“…Techniques like differential centrifugation (Wallace et al, 2003), chromatographic separation (Van Campenhout et al, 2008), and microscopic analysis (Marigómez et al, 2002) give the opportunity to study the internal distribution of the metals. However, it is not yet fully understood whether and how factors such as total tissue concentration, uptake rate and physiological condition are involved in the capacity of metal detoxification.…”