Shell thickening in Anodonta cygnea by induced acidosis

Exposure of zebra mussels to extracorporeal shock waves demonstrates formation of new mineralized tissue inside and outside the focus zone

The success rate of extracorporeal shock wave therapy (ESWT) for fracture nonunions in human medicine (i.e. radiographic union at 6 months after ESWT) is only approximately 75%. Detailed knowledge regarding the underlying mechanisms that induce bio-calcification after ESWT is limited. We analyzed the biological response within mineralized tissue of a new invertebrate model organism, the zebra mussel Dreissena polymorpha, after exposure with extracorporeal shock waves (ESWs). Mussels were exposed to ESWs with positive energy density of 0.4 mJ/mm² (A) or were sham exposed (B). Detection of newly calcified tissue was performed by exposing the mussels to fluorescent markers. Two weeks later, the A-mussels showed a higher mean fluorescence signal intensity within the shell zone than the B-mussels (P<0.05). Acoustic measurements revealed that the increased mean fluorescence signal intensity within the shell of the A-mussels was independent of the size and position of the focal point of the ESWs. These data demonstrate that induction of bio-calcification after ESWT may not be restricted to the region of direct energy transfer of ESWs into calcified tissue. The results of the present study are of relevance for better understanding of the molecular and cellular mechanisms that induce formation of new mineralized tissue after ESWT.

Effects of carbon dioxide on juveniles of the freshwater mussel (Lampsilis siliquoidea [Unionidae])

Carbon dioxide (CO₂ ) has shown promise as a tool to control movements of invasive Asian carp, but its effects on native freshwater biota have not been well studied. The authors evaluated lethal and sublethal responses of juvenile fatmucket (Lampsilis siliquoidea) mussels to CO₂ at levels (43-269 mg/L, mean concentration) that bracket concentrations effective for deterring carp movement. The 28-d lethal concentration to 50% of the mussels was 87.0 mg/L (95% confidence interval [CI] 78.4-95.9) and at 16-d postexposure, 76.0 mg/L (95% CI 62.9-90.3). A proportional hazards regression model predicted that juveniles could not survive CO₂ concentrations >160 mg/L for more than 2 wk or >100 mg/L CO₂ for more than 30 d. Mean shell growth was significantly lower for mussels that survived CO₂ treatments. Growth during the postexposure period did not differ among treatments, indicating recovery of the mussels. Also, CO₂ caused shell pitting and erosion. Behavioral effects of CO₂ included movement of mussels to the substrate surface and narcotization at the highest concentrations. Mussels in the 110 mg/L mean CO₂ treatment had the most movements in the first 3 d of exposure. If CO₂ is infused continuously as a fish deterrent, concentrations <76 mg/L are recommended to prevent juvenile mussel mortality and shell damage. Mussels may survive and recover from brief exposure to higher concentrations. Environ Toxicol Chem 2017;36:671-681. Published 2016 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

2,4-Dichlorophenoxyacetic acid alters intracellular pH and ion transport in the outer mantle epithelium of the bivalve Anodonta cygnea

Bivalve molluscs, due to their sedentary mode of life and filter-feeding behavior, are very susceptible to pollutant bioaccumulation and used as sentinel organisms in the assessment of environment pollution. Herein we aimed to determine the in vivo, ex vivo and in vitro effects of 2,4-dichlorophenoxyacetic acid (2,4-D), a widely used herbicide, in Anodonta cygnea shell growth mechanisms. For that, we evaluated the effect of 2,4-D (100 μM) exposure on the transepithelial short-circuit current (Isc), potential (Vt) and conductance (Gt), as well as on OME ion transport systems and intracellular pH (pHi). In vivo exposure to 2,4-D caused an increase of 50% on the Isc generated by OME and ex vivo addition of that compound to the apical side of OME also induced an Isc increase. Furthermore, 2,4-D was able to cause a pHi increase in isolated cells of OME. Noteworthy, when 2,4-D was added following the exposure to specific inhibitors of several membrane transporters identified as responsible for pHi maintenance in these cells, no significant effect was observed on pHi except when the V-type ATPase inhibitor was used, indicating an overlap with the effect of 2,4-D. Thus, we concluded that 2,4-D is able of enhancing the activity of the V-ATPases present on the OME of A. cygnea and that this effect seems to be due to a direct stimulation of those H(+) transporters present on the apical portion of the membrane of OME cells, which are vital for shell maintenance and growth. This study allows us to better understand the molecular mechanisms behind 2,4-D toxicity and its deleterious effect in aquatic ecosystems, with particular emphasis on those involved in shell formation of bivalves.

Effects of non-steroidal estrogen diethylstilbestrol on pH and ion transport in the mantle epithelium of a bivalve Anodonta cygnea

Freshwater bivalves are used as sentinel organisms to detect pollutants effects in the aquatic environment due to their sedentary nature, filter-feeding behaviour. We aimed to determine the in vivo, ex vivo and in vitro influence of Diethylstilbestrol (DES), a widely used synthetic non-steroidal estrogen and endocrine disruptor, in Anodonta cygnea shell growth mechanisms. For that, in vivo exposure to DES (0.75μM) during 15 days, in vitro and ex vivo exposure of outer mantle epithelium (OME) cells to DES (0.75μM), were performed followed by study of short-circuit current (Isc), transepithelial potential (Vt) and transepithelial conductance (Gt) as well as identification of membrane transport systems and intracellular pH (pHi). Our results show that in vivo exposure to DES decreases in 30% the OME Isc and ex vivo addition of DES to the basolateral side of OME also induced Isc decrease. Several membrane transporters such as V-type ATPases, Na(+)/H(+) exchangers, Na(+)-K(+) pump, Na(+)-driven and Na(+)-independent HCO3(-)/Cl(-) transporters and Na(+)/HCO3(-) co-transporter were identified as responsible for pHi maintenance in OME and noteworthy, DES caused a pHi decrease in OME cells similar to the effect observed when OME cells were exposed to 4,4'-diisothiocyanostilbene disulfonic acid (DIDS), an inhibitor of several bicarbonate membrane transporters. The addition of DIDS after OME cells exposure to DES did not cause any alteration. We concluded that DES is able to modulate membrane ion transport and pHi in the OME of A. cygnea and that this effect seems to be due to inhibition of HCO3(-)/Cl(-) co-transporters present on the basolateral membrane.

Ionic regulation and shell mineralization in the bivalve Anodonta cygnea (swan mussel) following heavy-metal exposure

Freshwater mussels are one of the most imperiled faunistic groups in the world and environmental exposure to toxic heavy metals, which result in deregulation of calcium absorption and deposition in the laboratory, may be a contributing factor in their decline. To address potential effects of heavy-metal exposure on calcium transport and metabolism in freshwater bivalves, adult Anodonta cygnea (L., 1758) were exposed to a sublethal concentration (1.0 × 10−6 mol/L) of essential (Zn2+ and Cu2+) or nonessential (Pb2+ and Cr3+) metal for 30 days in the laboratory. Inorganic composition of extrapallial, haemolymph, heart, and pericardium fluids, and kidney tissue, as well as shell morphology by scanning electron microscopy, were compared in treated and untreated mussels. Calcium levels in fluids varied after exposure to any of the metals investigated, although the magnitude and threshold of effect were metal- and compartment-specific. Ca2+ levels increased robustly in all fluids following exposure to Zn2+, Cu2+, or Cr3+, whereas levels decreased significantly in heart fluid alone following Pb2+ exposure (p < 0.05). In constrast to exposure to the other metals, Cu2+ revealed an interesting reverse-accumulation pattern, decreasing in the fluids but not in the kidney, where it clearly accumulates for excretion. In addition, whereas essential Cu2+ and Zn2+ are closely regulated, the nonessential metals Pb2+ and Cr3+ increase to very high levels. Drastic alterations in shell morphology, specifically the structure of border and inner pallial regions of the nacreous layer, were observed after Cu2+ or Cr3+ exposure. Collectively, data suggest that prolonged exposure to a sublethal concentration of these heavy metals can adversely affect compartmental calcium availability and shell composition in A. cygnea.

Acute physiological responses of the freshwater snail Elimia flava (Mollusca: Pleuroceridae) to environmental pH and calcium

The individual and interactive effects of environmental pH (7 [control], 6, 5, and 4) and calcium (0, 5, and 50 mg/L) were studied on hemolymph ions (pH, Ca(2+), total CO(2), Na(+), K(+)) and osmolality in the freshwater snail, Elimia flava, over a 72-h exposure. All hemolymph factors strongly differed with environmental pH. Snails exposed to pH 4 were inactive and experienced more dramatic ionic disturbances than snails at pH 5, 6, and 7, including reduced hemolymph pH, depressed Na(+) concentrations, and increased Ca(2+) and total CO(2) concentrations. There was an initial but transient increase in hemolymph K(+) over the 72 h exposure period. Environmental calcium ameliorated effects of acidification on hemolymph pH and Na(+), reducing the degree of depression in both variables irrespective of environmental pH or exposure time. In a separate experiment, effects of acidification on snail respiration were examined in which VO(2) was measured over 24 h in snails exposed to pH 7 and 4. Exposure to pH 4 caused a 64% reduction in oxygen uptake at 2 h and a maximum reduction (81%) at 11 h. Our results suggest that snails exposed to pH 4 cease interacting with the surrounding medium and use internal stores of CaCO(3) to buffer hemolymph acidification, whereas snails at pH 5 and higher appear to use environmental calcium as a buffer source. These results suggest an important role of environmental calcium in ameliorating the impacts of short-term, sublethal acidification.

Studies on a PMCA-like protein in the outer mantle epithelium of Anodonta cygnea: insights on calcium transcellular dynamics

Early studies on the outer mantle epithelium (OME) cells of the freshwater bivalve Anodonta cygnea (Linnaeus, 1758) revealed high ionic calcium concentrations by electrophysiological methods and subsequently a high tendency to reach an intracellular toxic condition. This toxicity could be neutralized by specific mechanisms in the cytosol of OME cells of A. cygnea. The present immunocytochemistry studies of OME cells by light and transmission electron microscopy (TEM) clearly showed a positive reaction of an antibody directed against the human plasma membrane Ca(2+)-ATPase 1 (PMCA-1) in the cytoplasm of OME cells. Also, western blot analysis of different fractions of OME cells with anti human PMCA-1 and C28R2 antibodies confirmed the presence of a PMCA-like protein with an unusual topographical localization and a molecular weight of only 70-80 kDa. These results lead us to speculate that this PMCA-like protein is distributed either in the plasma membrane or in the entire cytosol, where it eventually regulates intracellular calcium levels. Interestingly, the antibody reactions showed seasonal variations, being highest in OME samples prepared during summer when A. cygnea live under natural acidosis and absent in samples taken in winter conditions, which is in accordance with the seasonal variation of shell calcification rates. During winter, PMCA-1 antibody reaction was also detected in OME cells of animals kept only under experimentally induced acidosis conditions. Therefore, we assume that a functional role for this PMCA-like protein in the intracellular calcium regulation of OME cells during the mineralization of the shells of A. cygnea can be speculated.

Isolation, purification and characterization of glycosaminoglycans in the fluids of the mollusc Anodonta cygnea

The isolation, purification and characterization of Anodonta cygnea haemolymph, and extrapallial fluid glycosaminoglycans (Gags), which have high calcium affinity, were carried out in order to better understand the process of nacreous shell biomineralization. Our results show the existence of two different Gags with similar contents in the two fluids, throughout the year, but with significant seasonal variations for both. In the winter months, we identified by electrophoresis, only one kind of Gag chain (hyaluronic acid) while two different Gags (hyaluronic acid and heparan sulphate-like) from both fluids of A. cygnea were found in summer months. Quantification showed the total Gag fractions of both fluids in average, at their highest concentration (79.8 mg/L) in the highest calcification summer period. In contrast, the period of the year with the lowest concentration of total Gags (54.6 mg/L) occurred during the winter when calcification is reduced. This significant decrease between seasons is correlated mainly with the sulphated fraction, being 37.1 mg/L in the summer while only 9.2 mg/L in the winter haemolymph. The present data suggest that a heparan sulphate-like Gag has a relevant role in the biomineralization mechanisms acting as the calcium carbonate nucleator in the shell.

Cuticle Ultrastructure Changes in the Crab Scylla serrata Over the Molt Cycle

Morphological and chemical studies on the cuticle during the molt cycle of the crab Scylla serrata were performed in order to understand the layer formation. Cuticle ultrastructure was studied by scanning electron microscopy (SEM). Energy-dispersive, X-ray diffraction, and X-ray fluorescence analysis were used for identification of the elements and phases in the inner surface of the cuticle. In the first stage (A) of cuticle formation, a thin pellicle organized as an irregular fragmented structure is built. It is composed mainly of alpha-chitin/protein beta-keratin-like complexes where heterogeneous mineral nucleation occur. It is impregnated by ferric concretions, responsible for the brown colour of the carapace. At the beginning of the mineralization process, a spheroidal inorganic phase appears consisting of dicalcium phosphate dihydrate (DCPD) Ca/P=1.00, octacalcium phosphate (OCP) Ca/P=1.33 associated with hydromagnesite and bromapatite traces. During further cuticle development in the remaining A stage and in the beginning of the B stage, calcite and magnesian calcite are formed from the precursor calcium phosphate phase. The next development in the C stages is characterized by intense calcareous thickening consisting mainly of calcite and of magnesian calcite, which become the major mineral fraction of the cuticle. Organic-inorganic complex precipitations exhibit different aspects as spongiform, filamentary helicoidal, and concentric radial arrangements during C1, C2, and C3, respectively. During different stages of the cuticle formation in Scylla serrata, these mineral deposits may partially result from the balance among different organic contents, mainly between alpha-chitin and protein beta-keratin-like compounds. On the other hand, the calcium crystallization on apatite and calcite polymorphic structures may be influenced by variations of physico-chemical factors in the cuticle compartment. J. Exp. Zool. 293:414-426, 2002.

Cytometric, morphologic and enzymatic characterisation of haemocytes in Anodonta cygnea

The haemocytes in bivalve mussels are involved in many processes such as lesion repair, shell repair, elimination of small particles and toxic substances. In Anodonta cygnea there are two categories of haemolymph cells, the granulocytes and hyalinocytes. Two groups of cells were identified by flow cytometry and morphological studies: one with larger size and granularity representing 75%, and another group of cells (25%) which were approximately half the size. The cytochemical reactions showed peroxidase activity in the larger cells and a weak prophenoloxidase activity in the smaller cells. These characteristics suggest that the most common haemocytes are granulocytes and hyalinocytes are less common. Enzymatic studies showed clear activities of few enzymes in different compartments of the mantle. Both haemocytes presented significant variations for alpha-manosidase and beta-glucurosidase activities depending on the acid or alkaline pH. Almost all were sensitive to the pH changes, mainly the beta-galactosidase in the haemolymph plasma. On the contrary, the same enzymatic analysis in the extrapallial elements showed more stabilised activities. The simulation of acidic and alkaline condition with the observation of significant morphological and enzymatic activity changes, allow us to speculate some functional role, mainly in the haemolymph elements. The granulocytes may be speculated to have intense involvement in the digestion of small residues with the formation of calcareous stores while the hyalinocytes are more responsible for the elimination of soluble cytotoxic compounds.

The action of Cd, Cu, Cr, Zn, and Pb on fluid composition of Anodonta cygnea (L.): organic components

The heavy metals, Cd, Cu, Cr, Zn, and Pb, were used to incubate healthy specimens of the freshwater mussel species, Anodonta cygnea. Afterwards, their biological fluids, either haemolymph or extrapallial fluid were analyzed for the presence of several organic constituents, known to be important for biomineralization, such as proteins, glycosaminoglycans (GAGs) and glucosamine. Proteins were subjected to further study, namely through the total amino acid determination after acid hydrolysis. The most disturbing pollutants tested seem to be Pb, Zn, and Cr, which caused highly decreased overall compositions, namely with respect to protein, and glucosamine, in comparison to the control group. This suggests that this group contributes to a decrease of the metabolic activity, and thus mineralization, in the exposed animals.