Calcium regulation in crustaceans during the molt cycle: a review and update

'Dust you shall eat': The complex nutritional and functional considerations underlying a simple diet

Animals assimilate macronutrients and mineral nutrients in specific quantities and ratios to maximise fitness. To achieve this, animals must ingest different foods that contain the needed nutrients or facilitate the digestion of those nutrients. We explored how these multidimensional considerations affect the desert isopods (Hemilepistus reaumuri) curious food selection, using field and laboratory experiments. Wild isopods consumed three-fold more macronutrient-poor biological soil crust (BSC) than plant litter. Isopods tightly regulated macronutrient and calcium intake, but not phosphorus when eating the two natural foods and when artificial calcium and phosphorus sources substituted the BSC. Despite the equivalent calcium ingestion, isopods performed better when eating BSC compared to artificial foods. Isopods that consumed BSC sterilised by gamma-radiation ate more but grew slower than isopods that ate live BSC, implying that ingested microorganisms facilitate litter digestion. Our work highlights the need to reveal the multifaceted considerations that affect food-selection when exploring trophic-interactions.

The comparison and analysis of nutritional qualities of Chinese mitten crabs (Eriocheir sinensis) in rice field and pond culture modes

The nutritional quality of three edible parts (gonads, hepatopancreas and muscles) of Chinese mitten crabs (CMCs) from rice field culture and pond culture was firstly compared in our current study. It was found that the contents of mineral elements and volatile compounds in rice CMCs were superior to those in pond CMCs, and the antioxidant enzyme activities of rice CMCs were markedly higher than those of pond CMCs. Besides, the total free amino acid levels in the edible parts of pond CMCs were higher than those of rice CMCs. Compared with other tissues, the nucleotide and equivalent umami concentrations of the gonads in female rice CMCs were the maximum. Overall, both types of crabs demonstrated good nutritional quality, which met human nutrition and dietary needs. In comparison, the quality of rice CMCs was better than that of pond CMCs.

Deciphering Molecular Mechanisms Governing the Reproductive Molt of Macrobrachium nipponense: A Transcriptome Analysis of Ovaries across Various Molting Stages

The relationship between molting and reproduction has received more attention in economically important crustacean decapods. Molting and reproduction are synergistic events in Macrobrachium nipponense, but the molecular regulatory mechanisms behind them are unclear. In the current study, we performed Illumina sequencing for the ovaries of M. nipponense during the molt cycle (pre-molting, Prm; mid-molting, Mm; and post-molting, Pom). A total of 66.57 Gb of transcriptome data were generated through sequencing, resulting in the identification of 105,149 unigenes whose alignment ratio with the reference genome exceeded 87.57%. Differentially expressed genes (DEGs) were annotated through the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases for gene classification and pathway analysis. A total of twenty-six molt-related DEGs were found, and their expression patterns were examined across various molting stages. The KEGG enrichment analysis revealed that the key pathways involved in regulating the molting process of M. nipponense primarily include the mTOR, insect hormone biosynthesis, TGF-beta, and Wnt signaling pathways. Our transcriptomic data suggest that these pathways crosstalk with each other to regulate the synthesis and degradation of ecdysone throughout the molt cycle. The current study has deepened our understanding of the molecular mechanisms of crustacean molting and will serve as a basis for future studies of crustaceans and other molting animals.

Molecular characterization of TRPA1 and its function in temperature preference in Eriocheir sinensis

Chinese mitten crab (Eriocheir sinensis) is an economically important aquaculture species, and its growth and development are regulated by temperature, but the molecular mechanisms of the responses to temperature remain unclear. Herein, we identified TRPA1 from E. sinensis, a member of the TRP family of heat receptor potential channels, performed RACE cloning and bioinformatics analysis, and investigated the effect of TRPA1 on temperature responses and molting by real-time PCR and RNA interference (RNAi). The open reading frame of Es-TRPA1 is 3660 bp, and the encoded protein has a molecular weight of 136.91 kDa, and is expressed in embryos and juveniles. RNAi-mediated silencing decreased Es-TRPA1 expression in juvenile crabs, molting rate was decreased, mortality was increased, and crabs avoided cold areas (4 °C) much less than control juvenile crabs. The results suggest that Es-TRPA1 is involved in regulating temperature adaptation and molting processes in E. sinensis. The findings lay a foundation for further exploration of temperature regulation mechanisms in E. sinensis and other crustaceans.

Metal bioaccumulation in stygophilous amphipod Synurella ambulans in the hyporheic zone: The influence of environmental factors

Given the increasing need to protect vulnerable freshwater ecosystems and make them more resilient to human use and climate change, biomonitoring of the hyporheic zone (HZ), which plays a critical role in pollution attenuation, is essential. The aim of the present study was to assess the potential of the amphipod species Synurella ambulans as a bioindicator of metal contamination in the HZ of the Sava River (Croatia). Amphipods were collected during the four seasons at two sampling sites (average sampling depth 55 cm) differing in type (agricultural and urban) and intensity (diffuse and point source contamination) of anthropogenic influence, one located upstream (Medsave), and the other downstream (Jarun) of the wastewater treatment plant discharge. Concentrations of Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Rb, Sn, Zn, Ca, K, Mg and Na were measured in the interstitial water, sediments and specimens of S. ambulans by HR ICP-MS. Physicochemical parameters (temperature, DO, O₂ saturation, pH, conductivity, alkalinity, total water hardness, COD_KMnO4, nutrients) were measured in the interstitial water, while organic carbon was measured in the interstitial water and sediments. Metal concentrations in interstitial water and sediments were below thresholds set by environmental quality standards. Metal concentrations in S. ambulans were classified as follows: higher at the Jarun site (Al, Cr, Fe, Ni, Pb, Sn), higher at the Medsave site (Cd, Cu, Rb) and mostly comparable at both sites (Co, Mn, Zn). Bioaccumulation factors were generally higher at Jarun, with average values ranging from 322 to 143,278 L kg^-1. Bioaccumulation of metals in S. ambulans depended on various environmental factors, with metal exposure level and dissolved macro elements showing the strongest association with metals accumulated in S. ambulans. The findings provided the first evidence on the suitability of S. ambulans as a good bioindicator of chronic metal contamination in the HZ.

Can hypoosmotic shock and calcium influx lead to translocation of Aquaporin-1 in shrimp muscle cells?

The physiological variations during the crustacean molting cycle have intrigued researchers for many years. Maintaining osmotic homeostasis in the face of hemolymph dilution and dealing with dynamic intracellular and extracellular calcium fluctuations are challenges these animals continuously confront. It has recently been shown that water channels present in the cell membrane (aquaporins) are essential for water uptake during pre-molt and post-molt. This study aims to investigate whether hypoosmotic shock and intracellular and extracellular calcium variations can lead to translocation of aquaporin 1 (AQP-1) from the intracellular region to the plasma membrane during pre-molt and post-molt, thus allowing increased water flow in these stages. For this, we investigate in vitro the rapid change of AQP-1 positions in the abdominal muscle cells in the freshwater shrimp, P. argentinus. Using cell volume analysis and immunohistochemistry, we show that hypoosmotic conditions and an elevation of the intracellular and extracellular calcium concentrations are concurrent with the translocation of AQP-1 to the plasma membrane. These results indicate that calcium flux and hypoosmotic shock may be regulators of aquaporin 1 in the translocation process. This article is protected by copyright. All rights reserved.

Lead Inhibits Postecdysial Exoskeletal Calcification in the Blue Crab (Callinectes sapidus)

Postecdysial mineralization in crustaceans involves the deposition of carbonate salts, such as calcium carbonate, to the organic matrix. Because of the resemblance between Pb²⁺ and Ca²⁺ , the present study was carried out to investigate whether Pb is incorporated into the new shell during postecdysial mineralization using the blue crab (Callinectes sapidus) as the model crustacean. It was hypothesized that injected Pb would be deposited in the shell via calcium transporters in the epidermis during the mineralization process. Postecdysial blue crabs were injected with two doses of 5 µg Pb/g wet weight each in lead acetate, and then Pb, Ca, and Mg contents were analyzed in the exoskeleton, while only Pb bioaccumulation was quantified for the hepatopancreas, gills, muscles, and hemolymph. The results showed a statistically nonsignificant increase in exoskeletal Pb content in Pb-treated crabs compared to control, suggesting that exoskeletal Pb may not be a sensitive proxy for aquatic Pb pollution. There was a significant decrease in Ca content in Pb-treated crabs, suggesting that Pb hindered the deposition of Ca to crab exoskeleton, thereby obstructing calcification. A trend of a decrease in exoskeletal Mg was also observed in Pb-treated crabs. There was a significant increase in Pb content found in the gills, hepatopancreas, muscle, and hemolymph in Pb-treated crabs. The rank of the Pb level among three soft tissues in a decreasing order is hepatopancreas > gill > muscle. This is the first study to present evidence that Pb disrupts postecdysial exoskeletal calcification in a crustacean. Environ Toxicol Chem 2022;41:474-482. © 2021 SETAC.

Probiotic Effects of a Marine Purple Non-Sulfur Bacterium, Rhodovulum sulfidophilum KKMI01, on Kuruma Shrimp (Marsupenaeus japonicus)

Purple non-sulfur bacteria (PNSB) are used as probiotics in shrimp aquaculture; however, no studies have examined the probiotic effects of PNSB in shrimp at the gene expression level. In this study, we examined the effects of a marine PNSB, Rhodovulum sulfidophilum KKMI01, on the gene expression of kuruma shrimp (Marsupenaeus japonicus). Short-term (3 days) effects of R. sulfidophilum KKMI01 on the gene expression in shrimp were examined using small-scale laboratory aquaria experiments, while long-term (145 days) effects of R. sulfidophilum KKMI01 on the growth performance and gene expression were examined using 200-ton outdoor aquaria experiments. Gene expression levels were examined using qRT-PCR. Results of the short-term experiments showed the upregulation of several molting-related genes, including cuticle proteins, calcification proteins, and cuticle pigment protein, suggesting that PNSB stimulated the growth of shrimp. The upregulation of several immune genes, such as prophenoloxidase, antimicrobial peptides, and superoxide dismutase, was also observed. In the 145-day outdoor experiments, the average body weight at harvest time, survival rate, and feed conversion ratio were significantly improved in PNSB-treated shrimp, and upregulation of molting and immune-related genes were also observed. When PNSB cells were added to the rearing water, the effective dosage of PNSB was as low as 10³ cfu/mL, which was more than a million times dilution of the original PNSB culture (2–3 × 10⁹ cfu/mL), indicating that R. sulfidophilum KKMI01 provides a feasible and cost-effective application as a probiotic candidate in shrimp aquaculture.

Short communication: Effects of acute copper exposure on ionic regulation of the freshwater crab Aegla castro

Aeglids are unique freshwater decapods whose habitats are being impacted by metallic compounds, such as copper (Cu). Thus, we investigated the effects of acute Cu exposure on ionic regulation of Aegla castro. For this, male specimens in intermolt were collected from a reference stream and acclimated for 5 days in laboratory. After which, crabs were exposed to 11 μg L^-1 Cu (Cu11) or only to water (CTR) for 24 h. Hemolymph samples were withdrawn for the determination of Na⁺, K⁺, Ca²⁺, and Mg²⁺ concentrations and the posterior gills removed for the analysis of Na⁺/K⁺-ATPase, Ca²⁺-ATPase, H⁺-ATPase, and carbonic anhydrase (CA) activities. Increased Ca²⁺ and Mg²⁺ hemolymph concentrations were observed in animals from Cu11, when compared with CTR group. In addition, decreased activity of CA was observed in animals exposed to Cu. In the current study, alterations in Ca²⁺ and Mg²⁺concentrations probably indicate that animals activated exoskeleton reabsorption mechanisms, characteristic of the premolt. Therefore, increased Ca²⁺ and Mg²⁺ concentrations in hemolymph may indicate that a biochemical signal associated with the molting cycle was triggered by Cu exposure. Despite the known harmful effects of Cu on osmoregulatory enzymes, here we observed decreased activity only in CA. However, decreased activity of CA could trigger both acid-base imbalance and ionic disruption, since CA provides H⁺ and HCO₃^- for intracellular pH maintenance, and underpins Na⁺ and Cl^- for ionic regulation. Therefore, understanding how aeglids respond to metal contamination in laboratory conditions is crucial to assess their potential as an alternative biological model for aquatic ecotoxicology.

La dureza total del agua afecta la muda, calcificación, crecimiento y supervivencia de Cryphiops caementarius (Palaemonidae)

El objetivo de este estudio fue evaluar los efectos de diferentes niveles de dureza total del agua en la muda, calcificación del exoesqueleto, crecimiento y supervivencia de Cryphiops caementarius. Los camarones machos fueron colectados del río Pativilca (Lima, Perú) y cultivados en recipientes individuales dentro de acuarios (55 L). Se emplearon cuatro niveles de dureza total del agua (100, 200, 300 y 400 mg CaCO3 L-1), con tres repeticiones, respectivamente. Los camarones cultivados en agua con dureza de 300 mg L-1 tuvieron menor periodo de muda (26,7 días) y mayor frecuencia de mudas (tres mudas). El contenido de calcio del exoesqueleto del camarón incrementó (p < 0,05) de 25 a 31 % en agua con dureza de 100 y 400 mg L-1, respectivamente. El mayor grosor del exoesqueleto (144 µm en cefalotórax y 131 µm en abdomen) fue obtenido en agua con dureza de 400 mg L-1 y el menor grosor (93 µm en cefalotórax y abdomen) en 100 mg L-1. El crecimiento en longitud fue mayor (p < 0,05) en agua con durezas de 200 y 300 mg L-1. El crecimiento en peso fue similar (p > 0,05) entre tratamientos. La mayor supervivencia (> 94,4 %) se mantuvo en agua con durezas de hasta 300 mg L-1 y la menor supervivencia (77,8 %) fue con 400 mg L-1. La dureza total del agua de 200 y 300 mg L-1 es conveniente para el cultivo del camarón, pero dureza del agua mayor o menor a este rango afectan la muda, el crecimiento y la supervivencia por deficiencia o exceso de calcio acumulado, respectivamente en el exoesqueleto del camarón.

Basolateral Na+/Ca2+ exchanger 1 and Na+/K+-ATPase, which display light-enhanced gene and protein expression levels, could be involved in the absorption of exogenous Ca2+ through the ctenidium of the giant clam, Tridacna squamosa

Giant clams perform light-enhanced shell formation (calcification) and therefore need to increase the uptake of exogenous Ca²⁺ during illumination. The ctenidium of the fluted giant clam, Tridacna squamosa, is involved in light-enhanced Ca²⁺ uptake. It expresses the pore-forming voltage-gated calcium channel (VGCC) subunit alpha 1 (CACNA1) in the apical membrane of the epithelial cells, and the protein expression level of CACNA1 is upregulated in the ctenidium during illumination. This study aimed to elucidate the mechanism involved in the transport of the absorbed Ca²⁺ across the basolateral membrane of the ctenidial epithelial cells into the hemolymph. We obtained a homolog of Na⁺/Ca²⁺exchanger 1 (NCX1-like) from the ctenidium of T. squamosa, which comprised 2418 bp, encoding a protein of 806 amino acids (88.9 kDa). NCX1-like had a basolateral localization in the epithelial cells of the ctenidial filaments and tertiary water channels. Illumination resulted in significant increases in the transcript and protein levels of NCX1-like/NCX1-like in the ctenidium. Hence, NCX1-like could operate in conjunction with VGCC to increase the transport of Ca²⁺ from the ambient seawater into the hemolymph during illumination. Illumination also resulted in the upregulation of the gene and protein expression levels of Na⁺/K⁺-ATPase (NKA) α-subunit (NKAα/NKAα) in the ctenidium of T. squamosa. As light-enhanced extrusion of Ca²⁺ into the hemolymph through NCX1-like would lead to a greater influx of extracellular Na⁺, the increased expression of the basolateral NKA was required to augment the capacity of intracellular Na⁺ homeostasis.

Investigating the mechanism of vanadium toxicity in freshwater organisms

Vanadium (V) could present a risk for aquatic organisms from the Alberta oil sands region, if present in high concentrations. An industry pilot project has used petroleum coke (PC) as a sorbent to remove organic toxicants from oil sands process-affected water (OSPW), but it also caused V to leach from PC into the OSPW, reaching concentrations of up to 7 mg V/L (a level known to be toxic to aquatic organisms). Vanadium is a transition metal with several oxidation states, which could potentially elicit its toxicity through either ion imbalance or oxidative stress. This study investigated the effect of V on Daphnia magna and Oncorhynchus mykiss. Daphinds and O. mykiss were exposed to concentrations of V up to their respective calculated median lethal concentration (LC₅₀): 3 mg V/L for D. magna and 7 mg V/L for O. mykiss. For both organisms, the influence of V on sodium flux and whole body sodium was evaluated. Its effect on whole body calcium and the oxidative stress responses in O. mykiss at the gill and liver levels was also studied. Results suggested that 3.1 mg V/L for D. magna and 6.8 mg V/L for O. mykiss caused an overall increase in sodium influx in both the daphnids and rainbow trout. However, concentrations of V ranging between 0.2 and 4 mg V/L for D. magna and 1.8 and 6 mg V/L for O. mykiss reduced whole body sodium in both organisms and whole body calcium in O. mykiss. Concentrations above 3.6 mg V/L caused significant lipid peroxidation in the gills and liver of rainbow trout, while 1.9 mg V/L produced a substantial decrease in the fish gill GSH:GSSG ratio, but no change in the ratio between these thiols in the liver. Concentrations of 6.62 mg V/L sharply increased catalase activity in the liver but not in the gills. Neither liver nor gill superoxide dismutase was altered by V. Overall, results suggest that both ion imbalance and oxidative stress are part of the mechanism of toxicity of V in D. magna and O. mykiss and that further research is warranted to fully elucidate the mechanism(s) of V toxicity in aquatic organisms.

Multi-species transcriptomics reveals evolutionary diversity in the mechanisms regulating shrimp tail muscle excitation-contraction coupling

The natural flight response in shrimp is powered by rapid contractions of the abdominal muscle fibres to propel themselves backwards away from perceived danger. This muscle contraction is dependent on repetitive depolarization of muscle plasma membrane, triggering tightly spaced cytoplasmic [Ca²⁺] transients and rapidly rising tetanic force responses. To achieve such high amplitude and high frequency of Ca²⁺ transients requires a high abundance of sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPase (SERCA) to rapidly clear cytoplasmic Ca²⁺ between each transient and an efficient Ca²⁺ release system consisting of the Ryanodine Receptor (RyR), and voltage gated Ca²⁺ channels (Ca_Vs). With the aim to expand our knowledge of muscle gene function and identify orthologous genes regulating muscle excitation-contraction (EC) coupling, this study assembled nine Penaeid shrimp muscle transcriptomes. On average, the nine transcriptomes contained 27,000 contigs, with an annotation rate of 36% and a BUSCO completeness of 70%. Despite maintaining their function, the crustacean RyR and Ca_V proteins showed evidence of significant diversification from mammalian orthologs, while SERCA remained more conserved. Several key components of protein interaction were conserved, while others showed distinct crustacean specific evolutionary adaptations. Lastly, this study revealed approximately 1,000 orthologous genes involved in muscle specific processes present across all nine species.

The effect of exuviae ingestion on lysosomal calcium accumulation and the presence of exosomes in the hepatopancreas of Porcellio scaber

The hepatopancreas of isopods has major functions in food digestion and storage of carbohydrates and lipids. Also, it stores essential and accumulates xenobiotic metals in lysosomal granules within the two major cell types, the S- and B-cells of the tissue. A µCT study on moulting Porcellio scaber has shown mineral within the hepatopancreas lumen, when the animal has ingested their shed cuticle after moulting, suggesting recycling of mineral from the exuviae. This study aims to reveal if the lysosomal metal containing granules store calcium originating from the ingested exuviae. Therefore, we investigated the effect of cuticle ingestion on the elemental composition of the hepatopancreas granules of P. scaber, using electron probe X-ray microanalysis. For the preservation of diffusible elements, samples were high pressure frozen and freeze substituted in acetone and we used Propane-1,3-diol as a floatation medium for sections. We analyzed S- and B-cells of animals in the postmoult and intermoult stage that have ingested their exuviae and, as a negative control, cells from postmoult animals that have not ingested their exuviae. STEM and TEM were used for the investigation of the ultrastructure. Unexpectedly, the cryo-fixed samples contain numerous extracellular vesicles (exosomes) and many multivesicular bodies containing pro-exosomes. We show a significant increase of calcium, copper, zinc and sulphur within the metal granules upon exuviae ingestion, and, after 9 days, a reduction of calcium and zinc. The results indicate transitory storage of calcium from the exuviae within the metal granules and its subsequent utilization in cuticle mineralization.

Terebratulide brachiopod shell biomineralization by mantle epithelial cells

To understand mineral transport pathways for shell secretion and to assess differences in cellular activity during mineralization, we imaged with TEM and FE-SEM ultrastructural characteristics of outer mantle epithelium (OME) cells. Imaging was carried out on Magellania venosa shells embedded/etched, chemically fixed/decalcified and high-pressure frozen/freeze-substituted samples from the commissure, central shell portions and from puncta. Imaging results are complemented with morphometric evaluations of volume fractions of membrane-bound organelles. At the commissure the OME consists of several layers of cells. These cells form oblique extensions that, in cross-section, are round below the primary layer and flat underneath fibres. At the commissure the OME is multi-cell layered, in central shell regions it is single-cell layered. When actively secreting shell carbonate extrapallial space is lacking, because OME cells are in direct contact with the calcite of the forming fibres. Upon termination of secretion, OME cells attach via apical hemidesmosomes to extracellular matrix membranes that line the proximal surface of fibres. At the commissure volume fractions for vesicles, mitochondria and lysosomes are higher relative to single-cell layered regions, whereas for endoplasmic-reticulum and Golgi apparatus there is no difference. FE-SEM, TEM imaging reveals the lack of extrapallial space between OME cells and developing fibres. In addition, there is no indication for an amorphous precursor within fibres when these are in active secretion mode. Accordingly, our results do not support transport of minerals by vesicles from cells to sites of mineralization, rather by transfer of carbonate ions via transport mechanisms associated with OME cell membranes.

Ocean acidification: effects of pH on 45Ca uptake by lobster branchiostegites

Gill chambers of the Atlantic lobster, Homarus americanus, possess three structures that are involved with respiration and ion regulation: gill filaments, epipodites, and branchiostegites. This paper describes ion transport mechanisms present in the plasma membranes of branchiostegite epithelial cells and the effects of pH on the uptake of ⁴⁵Ca by these processes. Partially purified membrane vesicles (PPMV) of branchiostegite cells were produced by a homogenization/centrifugation method that has previously been used to define ion transport processes in both crab and lobster gill tissues. In the present study, lobster branchiostegite PPMV ⁴⁵Ca uptake was highest at pH 8.5 and lowest at pH values between 6.0 and 7.0 (p < 0.02). At pH 8.0, ⁴⁵Ca uptake was a biphasic process consisting of a saturable process at low [Ca] and a linear process at higher [Ca]. At pH 6.0, ⁴⁵Ca uptake was only a linear process and paralleled linear uptake at pH 8.0. A valinomycin/K⁺-induced membrane potential (PD, inside negative) doubled ⁴⁵Ca uptake at pH 7.0 above that in the absence of a PD (p < 0.05). An induced PD at pH 8.0 did not significantly (p > 0.05) affect ⁴⁵Ca uptake observed in the absence of a PD, but was threefold greater than uptake at pH 7.0 in the absence of a PD (p < 0.05). Amiloride (2 mM) did not affect ⁴⁵Ca uptake at pH 8.0, but 2 mM amiloride + 100 µM verapamil reduced uptake by approximately 50%. In the presence of both 2 mM amiloride + 100 µM verapamil, 15 s ⁴⁵Ca influx at pH 8.5 was a hyperbolic function of [Ca] (0.1-5 mM) (K_m = 4.2 ± 0.3 mM; J_max = 9792 ± 439 pmol/mg protein × 15 s). ⁴⁵Ca influxes at pH 7.5 under the same conditions were also hyperbolic with K_m = 8.3 ± 1.4 mM; J_max = 10732 ± 1250 pmol/mg protein × 15 s. K_m values were significantly different (p < 0.05), but J_max values were not (p > 0.05). These results suggest that ⁴⁵Ca uptake by lobster branchiostegites may have occurred by the combination of diffusion through a verapamil-inhibited calcium channel and carrier-mediated transport by amiloride-insensitive, electroneutral, 1Ca²⁺/2H⁺ antiporters. Decreased pH, as might occur during ocean acidification, did not appear to modify calcium diffusion through the channels, but protons acted as competitive inhibitors of calcium transport by carrier-mediated antiport. Decreased calcium uptake with continued ocean acidification may significantly affect calcification processes during periodic molting, potentially influencing mortality.

Comparative molecular analyses of select pH- and osmoregulatory genes in three freshwater crayfish Cherax quadricarinatus, C. destructor and C. cainii

Systemic acid-base balance and osmotic/ionic regulation in decapod crustaceans are in part maintained by a set of transport-related enzymes such as carbonic anhydrase (CA), Na⁺/K⁺-ATPase (NKA), H⁺-ATPase (HAT), Na⁺/K⁺/2Cl⁻ cotransporter (NKCC), Na⁺/Cl⁻/HCO\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}${}_{3}^{-}$\end{document}3− cotransporter (NBC), Na⁺/H⁺ exchanger (NHE), Arginine kinase (AK), Sarcoplasmic Ca⁺²-ATPase (SERCA) and Calreticulin (CRT). We carried out a comparative molecular analysis of these genes in three commercially important yet eco-physiologically distinct freshwater crayfish, Cherax quadricarinatus, C. destructor and C. cainii, with the aim to identify mutations in these genes and determine if observed patterns of mutations were consistent with the action of natural selection. We also conducted a tissue-specific expression analysis of these genes across seven different organs, including gills, hepatopancreas, heart, kidney, liver, nerve and testes using NGS transcriptome data. The molecular analysis of the candidate genes revealed a high level of sequence conservation across the three Cherax sp. Hyphy analysis revealed that all candidate genes showed patterns of molecular variation consistent with neutral evolution. The tissue-specific expression analysis showed that 46% of candidate genes were expressed in all tissue types examined, while approximately 10% of candidate genes were only expressed in a single tissue type. The largest number of genes was observed in nerve (84%) and gills (78%) and the lowest in testes (66%). The tissue-specific expression analysis also revealed that most of the master genes regulating pH and osmoregulation (CA, NKA, HAT, NKCC, NBC, NHE) were expressed in all tissue types indicating an important physiological role for these genes outside of osmoregulation in other tissue types. The high level of sequence conservation observed in the candidate genes may be explained by the important role of these genes as well as potentially having a number of other basic physiological functions in different tissue types.

Toxicological perspective on the osmoregulation and ionoregulation physiology of major ions by freshwater animals: Teleost fish, crustacea, aquatic insects, and Mollusca

Anthropogenic sources increase freshwater salinity and produce differences in constituent ions compared with natural waters. Moreover, ions differ in physiological roles and concentrations in intracellular and extracellular fluids. Four freshwater taxa groups are compared, to investigate similarities and differences in ion transport processes and what ion transport mechanisms suggest about the toxicity of these or other ions in freshwater. Although differences exist, many ion transporters are functionally similar and may belong to evolutionarily conserved protein families. For example, the Na+ /H+ -exchanger in teleost fish differs from the H+ /2Na+ (or Ca2+ )-exchanger in crustaceans. In osmoregulation, Na+ and Cl- predominate. Stenohaline freshwater animals hyperregulate until they are no longer able to maintain hypertonic extracellular Na+ and Cl- concentrations with increasing salinity and become isotonic. Toxic effects of K+ are related to ionoregulation and volume regulation. The ionic balance between intracellular and extracellular fluids is maintained by Na+ /K+ -adenosine triphosphatase (ATPase), but details are lacking on apical K+ transporters. Elevated H+ affects the maintenance of internal Na+ by Na+ /H+ exchange; elevated HCO3- inhibits Cl- uptake. The uptake of Mg2+ occurs by the gills or intestine, but details are lacking on Mg2+ transporters. In unionid gills, SO42- is actively transported, but most epithelia are generally impermeant to SO42- . Transporters of Ca2+ maintain homeostasis of dissolved Ca2+ . More integration of physiology with toxicology is needed to fully understand freshwater ion effects. Environ Toxicol Chem 2017;36:576-600. 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.

Convergent Evolution of the Osmoregulation System in Decapod Shrimps

In adaptating to different aquatic environments, seawater (SW) and freshwater (FW) shrimps have exploited different adaptation strategies, which should generate clusters of genes with different adaptive features. However, little is known about the genetic basis of these physiological adaptations. Thus, in this study, we performed comparative transcriptomics and adaptive evolution analyses on SW and FW shrimps and found that convergent evolution may have happened on osmoregulation system of shrimps. We identified 275 and 234 positively selected genes in SW and FW shrimps, respectively, which enriched in the functions of ion-binding and membrane-bounded organelles. Among them, five (CaCC, BEST2, GPDH, NKA, and Integrin) and four (RasGAP, RhoGDI, CNK3, and ODC) osmoregulation-related genes were detected in SW and FW shrimps, respectively. All five genes in SW shrimps have been reported to have positive effects on ion transportation, whereas RasGAP and RhoGDI in FW shrimps are associated with negative control of ion transportation, and CNK3 and ODC play central roles in cation homeostasis. Besides, the phylogenetic tree reconstructed from the positively selected sites separated the SW and FW shrimps into two groups. Distinct subsets of parallel substitutions also have been found in these osmoregulation-related genes in SW and FW shrimps. Therefore, our results suggest that distinct convergent evolution may have occurred in the osmoregulation systems of SW and FW shrimps. Furthermore, positive selection of osmoregulation-related genes may be beneficial for the regulation of water and salt balance in decapod shrimps.

Voltage Dependence of a Neuromodulator-Activated Ionic Current

The neuromodulatory inward current (IMI) generated by crab Cancer borealis stomatogastric ganglion neurons is an inward current whose voltage dependence has been shown to be crucial in the activation of oscillatory activity of the pyloric network of this system. It has been previously shown that IMI loses its voltage dependence in conditions of low extracellular calcium, but that this effect appears to be regulated by intracellular calmodulin. Voltage dependence is only rarely regulated by intracellular signaling mechanisms. Here we address the hypothesis that the voltage dependence of IMI is mediated by intracellular signaling pathways activated by extracellular calcium. We demonstrate that calmodulin inhibitors and a ryanodine antagonist can reduce IMI voltage dependence in normal Ca(2+), but that, in conditions of low Ca(2+), calmodulin activators do not restore IMI voltage dependence. Further, we show evidence that CaMKII alters IMI voltage dependence. These results suggest that calmodulin is necessary but not sufficient for IMI voltage dependence. We therefore hypothesize that the Ca(2+)/calmodulin requirement for IMI voltage dependence is due to an active sensing of extracellular calcium by a GPCR family calcium-sensing receptor (CaSR) and that the reduction in IMI voltage dependence by a calmodulin inhibitor is due to CaSR endocytosis. Supporting this, preincubation with an endocytosis inhibitor prevented W7 (N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride)-induced loss of IMI voltage dependence, and a CaSR antagonist reduced IMI voltage dependence. Additionally, myosin light chain kinase, which is known to act downstream of the CaSR, seems to play a role in regulating IMI voltage dependence. Finally, a Gβγ-subunit inhibitor also affects IMI voltage dependence, in support of the hypothesis that this process is regulated by a G-protein-coupled CaSR.

Effects of seawater alkalinity on calcium and acid-base regulation in juvenile European lobster (Homarus gammarus) during a moult cycle

Fluxes of NH4(+) (acid) and HCO3(-) (base), and whole body calcium content were measured in European lobster (Homarus gammarus) during intermoult (megalopae stage), and during the first 24h for postmoult juveniles under control (~2000 μeq/L) and low seawater alkalinity (~830 μeq/L). Immediately after moulting, animals lost 45% of the total body calcium via the shed exoskeleton (exuvia), and only 11% was retained in the uncalcified body. At 24h postmoult, exoskeleton calcium increased to ~46% of the intermoult stage. Ammonia excretion was not affected by seawater alkalinity. After moulting, bicarbonate excretion was immediately reversed from excretion to uptake (~4-6 fold higher rates than intermoult) over the whole 24h postmoult period, peaking at 3-6h. These data suggest that exoskeleton calcification is not completed by 24h postmoult. Low seawater alkalinity reduced postmoult bicarbonate uptake by 29% on average. Net acid-base flux (equivalent to net base uptake) followed the same pattern as HCO3(-) fluxes, and was 22% lower in low alkalinity seawater over the whole 24h postmoult period. The common occurrence of low alkalinity in intensive aquaculture systems may slow postmoult calcification in juvenile H. gammarus, increasing the risk of mortalities through cannibalism.

The proteomic response of cheliped myofibril tissue in the eurythermal porcelain crab Petrolisthes cinctipes to heat shock following acclimation to daily temperature fluctuations

The porcelain crab Petrolisthes cinctipes lives under rocks and in mussel beds in the mid-intertidal zone where it experiences immersion during high tide and saturating humid conditions in air during low tide, which can increase habitat temperature by up to 20°C. To identify the biochemical changes affected by increasing temperature fluctuations and subsequent heat shock, we acclimated P. cinctipes for 30 days to one of three temperature regimes: (1) constant 10°C, (2) daily temperature fluctuations between 10 and 20°C (5 h up-ramp to 20°C, 1 h down-ramp to 10°C) and (3) 10–30°C (up-ramp to 30°C). After acclimation, animals were exposed to either 10°C or a 30°C heat shock to analyze the proteomic changes in claw muscle tissue. Following acclimation to 10–30°C (measured at 10°C), enolase and ATP synthase increased in abundance. Following heat shock, isoforms of arginine kinase and glycolytic enzymes such as aldolase, triose phosphate isomerase and glyceraldehyde 3-phosphate dehydrogenase increased across all acclimation regimes. Full-length isoforms of hemocyanin increased abundance following acclimation to 10–30°C, but hemocyanin fragments increased after heat shock following constant 10°C and fluctuating 10–20°C, possibly playing a role as antimicrobial peptides. Following constant 10°C and fluctuating 10–20°C, paramyosin and myosin heavy chain type-B increased in abundance, respectively, whereas myosin light and heavy chain decreased with heat shock. Actin-binding proteins, which stabilize actin filaments (filamin and tropomyosin), increased during heat shock following 10–30°C; however, actin severing and depolymerization proteins (gelsolin and cofilin) increased during heat shock following 10–20°C, possibly promoting muscle fiber restructuring. RAF kinase inhibitor protein and prostaglandin reductase increased during heat shock following constant 10°C and fluctuating 10–20°C, possibly inhibiting an immune response during heat shock. The results suggest that ATP supply, muscle fiber restructuring and immune responses are all affected by temperature fluctuations and subsequent acute heat shock in muscle tissue. Furthermore, although heat shock after acclimation to constant 10°C and fluctuating 10–30°C showed the greatest effects on the proteome, moderately fluctuating temperatures (10–20°C) broadened the temperature range over which claw muscle was able to respond to an acute heat shock with limited changes in the muscle proteome.

Analysis of gene expression in Homarus americanus larvae exposed to sublethal concentrations of endosulfan during metamorphosis

Agricultural pesticide runoff has been suspected as the cause of numerous fish kills in rivers throughout Prince Edward Island but the impact on the surrounding marine environment is unknown. Endosulfan, an organochlorine pesticide, is a potent neurotoxin and molt inhibitor used to combat the Colorado potato beetle however it has the potential to affect non-target organisms including the American lobster (Homarus americanus). Metamorphosis is a critical stage of development and the effects of contaminant exposure during this time are largely unknown in lobster. A 14day endosulfan exposure was performed to identify the effects on survival, development and gene expression in lobster larvae during metamorphosis; all of which were predicted to be negatively impacted. The higher endosulfan concentrations resulted in greater mortality and a significant increase in the number of days required to reach metamorphosis in surviving animals. A custom made H. americanus microarray was used for monitoring the changes in expression of 14,592 genes at the termination of the exposure. Genes with >1.5 fold change and identified as being significant at p<0.05 using one-way ANOVA were selected for further analysis. A total of 707 genes were identified as being significantly differentiated, however with only ~40% annotation of the array, the majority of these genes were unknown. Annotated genes of interest were involved in many processes: development, metabolism, immunity and oxidative stress response and gene regulation. Nine genes of interest (histone H1, farnesoic acid O-methyltransferase, cuticle protein, glutathione S-transferase, thioredoxin, NADH dehydrogenase, ecdysone nuclear receptor Fushi tarazu F1 (FTZ-F1), ferritin and ecdysone inducible protein E75 (EIP-E75)) were selected for RT-qPCR validation of the microarray results. The RT-qPCR method was more sensitive than the microarray yet detected similar expression patterns. The two highest endosulfan concentrations resulted in increased mortalities, developmental delays in reaching metamorphosis and significant changes in gene expression. This research provides a foundation for using microarray gene expression profiles as screening tools for exploring the impact of environmental contaminants on lobster.

An evaluation of muscle maintenance costs during fiber hypertrophy in the lobster Homarus americanus: are larger muscle fibers cheaper to maintain?

Large muscle fiber size imposes constraints on muscle function while imparting no obvious advantages, making it difficult to explain why muscle fibers are among the largest cell type. Johnston and colleagues proposed the 'optimal fiber size' hypothesis, which states that some fish have large fibers that balance the need for short diffusion distances against metabolic cost savings associated with large fibers. We tested this hypothesis in hypertrophically growing fibers in the lobster Homarus americanus. Mean fiber diameter was 316±11 μm in juveniles and 670±26 μm in adults, leading to a surface area to volume ratio (SA:V) that was 2-fold higher in juveniles. Na(+)/K(+)-ATPase activity was also 2-fold higher in smaller fibers. (31)P-NMR was used with metabolic inhibitors to determine the cost of metabolic processes in muscle preparations. The cost of Na(+)/K(+)-ATPase function was also 2-fold higher in smaller than in larger diameter fibers. Extrapolation of the SA:V dependence of the Na(+)/K(+)-ATPase over a broad fiber size range showed that if fibers were much smaller than those observed, maintenance of the membrane potential would constitute a large fraction of whole-animal metabolic rate, suggesting that the fibers grow large to reduce maintenance costs. However, a reaction-diffusion model of aerobic metabolism indicated that fibers in adults could attain still larger sizes without diffusion limitation, although further growth would have a negligible effect on cost. Therefore, it appears that decreased fiber SA:V makes larger fibers in H. americanus less expensive to maintain, which is consistent with the optimal fiber size hypothesis.

Effects of elevated seawater pCO(2) on gene expression patterns in the gills of the green crab, Carcinus maenas

Background

The green crab Carcinus maenas is known for its high acclimation potential to varying environmental abiotic conditions. A high ability for ion and acid-base regulation is mainly based on an efficient regulation apparatus located in gill epithelia. However, at present it is neither known which ion transport proteins play a key role in the acid-base compensation response nor how gill epithelia respond to elevated seawater pCO₂ as predicted for the future. In order to promote our understanding of the responses of green crab acid-base regulatory epithelia to high pCO₂, Baltic Sea green crabs were exposed to a pCO₂ of 400 Pa. Gills were screened for differentially expressed gene transcripts using a 4,462-feature microarray and quantitative real-time PCR.

Results

Crabs responded mainly through fine scale adjustment of gene expression to elevated pCO₂. However, 2% of all investigated transcripts were significantly regulated 1.3 to 2.2-fold upon one-week exposure to CO₂ stress. Most of the genes known to code for proteins involved in osmo- and acid-base regulation, as well as cellular stress response, were were not impacted by elevated pCO₂. However, after one week of exposure, significant changes were detected in a calcium-activated chloride channel, a hyperpolarization activated nucleotide-gated potassium channel, a tetraspanin, and an integrin. Furthermore, a putative syntaxin-binding protein, a protein of the transmembrane 9 superfamily, and a Cl^-/HCO₃^- exchanger of the SLC 4 family were differentially regulated. These genes were also affected in a previously published hypoosmotic acclimation response study.

Conclusions

The moderate, but specific response of C. maenas gill gene expression indicates that (1) seawater acidification does not act as a strong stressor on the cellular level in gill epithelia; (2) the response to hypercapnia is to some degree comparable to a hypoosmotic acclimation response; (3) the specialization of each of the posterior gill arches might go beyond what has been demonstrated up to date; and (4) a re-configuration of gill epithelia might occur in response to hypercapnia.

ATP pulse and calcium homeostasis in cells from hepatopancreas of Dilocarcinus pagei, a freshwater crab

Calcium (Ca) is critical for crustaceans due to their molting cycle and its presence in the carapace as calcium carbonate, apart from the usual functions of Ca, such as cell signalling. Ca transport in Dilocarcinus pagei, a freshwater crab, was studied in isolated cells from hepatopancreas to further characterize Ca transport mechanisms in these crabs. Cells were isolated and loaded with Fluo-3, a calcium fluorescent dye. Three different cell treatments were performed: Group 1 cells were Ca free during cell dissociation, and calcium was present (at 1 mM) for fluorescence cell loading and transport experiments (FC); Group 2 cells were calcium free during cell dissociation and for transport experiments, but not during cell loading (LC); and Group 3 cells were Ca free during cell dissociation, cell loading and transport experiments (WC). Intracellular Ca was recorded through time after ATP was added to the cells and ATP caused an increase in Ca efflux within 30s in all cells. WC cells showed the smallest Ca efflux compared to the other cells, probably because it was intracellularly Ca "depleted". Vanadate and amiloride decreased the Ca efflux when ATP was added to the cells, while verapamil did not cause any effect in Ca efflux, confirming the presence of a Ca(2+)-ATPase sensitive to vanadate in hepatopancreas of D. pagei. In a different set of experiments, cells were also exposed to a Ca pulse of 1 and 10mM during 180 s. 10mM Ca increased intracellular Ca compared to 1mM, and the increase was not recovered during the experimental time. Additionally, Ca influx was reduced by verapamil and amiloride, but not completely. The results suggest that Ca influx probably occurs through an undefined exchanger, apart from Ca channels (verapamil sensitive) and electrogenic 1 Na(+)(1H(+))/1 Ca(2+) exchanger (amiloride-sensitive). Similarities between freshwater and seawater crabs, lobsters and crayfish in relation to plasma membrane Ca transporters, although the environment where they live is quite diverse, suggest that universal mechanisms for Ca homeostasis are widespread among crustaceans.

Na(+)-K(+)-ATPase and Ca(2+) clearance proteins in smooth muscle: a functional unit

The Na(+)-K(+)-ATPase (NKA) can affect intracellular Ca(2+) concentration regulation via coupling to the Na(+)-Ca(2+) exchanger and may be important in myogenic tone. We previously reported that in mice carrying a transgene for the NKA alpha(2)-isoform in smooth muscle (alpha(2sm+)), the alpha(2)-isoform protein as well as the alpha(1)-isoform (not contained in the transgene) increased to similar degrees (2-7-fold). Aortas from alpha(2sm+) mice relaxed faster from a KCl-induced contraction, hypothesized to be related to more rapid Ca(2+) clearance. To elucidate the mechanisms underlying this faster relaxation, we therefore measured the expression and distribution of proteins involved in Ca(2+) clearance. Na(+)-Ca(2+) exchanger, sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA), and plasma membrane Ca(2+)-ATPase (PMCA) proteins were all elevated up to approximately fivefold, whereas actin, myosin light chain, and calponin proteins were not changed in smooth muscle from alpha(2sm+) mice. Interestingly, the corresponding Ca(2+) clearance mRNA levels were unchanged. Immunocytochemical data indicate that the Ca(2+) clearance proteins are distributed similarly in wild-type and alpha(2sm+) aorta cells. In studies measuring relaxation half-times from a KCl-induced contraction in the presence of pharmacological inhibitors of SERCA and PMCA, we estimated that together these proteins were responsible for approximately 60-70% of relaxation in aorta. Moreover, the percent contribution of SERCA and PMCA to relaxation rates in alpha(2sm+) aorta was not significantly different from that in wild-type aorta. The coordinate expressions of NKA and Ca(2+) clearance proteins without change in the relative contributions of each individual protein to smooth muscle function suggest that NKA may be but one component of a larger functional Ca(2+) clearance system.

Reciprocal changes in calcification of the gastrolith and cuticle during the molt cycle of the red claw crayfish Cherax quadricarinatus

Mobilization of calcium during the molt cycle from the cuticle to transient calcium deposits is widely spread in crustaceans. The dynamics of calcium transport to transient calcium deposits called gastroliths and to the cuticle over the course of the molt cycle were studied in the crayfish Cherax quadricarinatus. In this species, calcium was deposited in the gastroliths during premolt and transported back to the cuticle during postmolt, shown by digital X-ray radiograph analysis. The predominant mineral in the crayfish is amorphous calcium carbonate embedded in an organic matrix composed mainly of chitin. Scanning electron micrographs of the cuticle during premolt showed that the endocuticle and parts of the exocuticle were the source of most of the labile calcium, while the epicuticle did not undergo degradation and remained mineralized throughout the molt cycle. The gastroliths are made of concentric layers of amorphous calcium carbonate intercalated between chitinous lamella. Measurements of pH and calcium levels during gastrolith deposition showed that calcium concentrations in the gastroliths, stomach, and muscle were about the same (10 to 11 mmol l(-1)). On the other hand, pH varied greatly, from 8.7+/-0.15 in the gastrolith cavity through 7.6+/-0.2 in muscle to 6.9+/-0.5 in the stomach.

A structure-function analysis of ion transport in crustacean gills and excretory organs

Osmotic and ionic regulation in the Crustacea is mostly accomplished by the multifunctional gills, together with the excretory organs. In addition to their role in gas exchange, the gills constitute organs of active, transepithelial, ion transport, an activity of major importance that underlies many essential physiological functions like osmoregulation, calcium homeostasis, ammonium excretion and extracellular pH regulation. This review focuses on structure-function relationships in crustacean gills and excretory effectors, from the organ to molecular levels of organization. We address the diversity of structural architectures encountered in different crustacean gill types, and in constituent cell types, before examining the physiological mechanisms of Na(+), Cl(-), Ca(2+) and NH(4)(+) transport, and of acid-base equivalents, based on findings obtained over the last two decades employing advanced techniques. The antennal and maxillary glands constitute the principal crustacean excretory organs, which have received less attention in functional studies. We examine the diversity present in antennal and maxillary gland architecture, highlighting the structural similarities between both organ types, and we analyze the functions ascribed to each glandular segment. Emphasis is given to volume and osmoregulatory functions, capacity to produce dilute urine in freshwater crustaceans, and the effect of acclimation salinity on urine volume and composition. The microanatomy and diversity of function ascribed to gills and excretory organs are appraised from an evolutionary perspective, and suggestions made as to future avenues of investigation that may elucidate evolutionary and adaptive trends underpinning the invasion and exploitation of novel habitats.

Analysis of calcium concentration fluctuations in hepatopancreatic R cells of Marsupenaeus japonicus during the molting cycle

In this study we examined the fluctuations of the intracellular calcium concentration in isolated hepatopancreatic R cells during the four molting stages of the prawn Marsupenaeus japonicus. In addition, we used the Fura-2-AM fluorescence technique to investigate the release of calcium from mitochondria and ATP-sensitive calcium stores (endoplasmic reticulum (ER), Golgi, and nucleus) into cytoplasm during the molting cycle. Results demonstrate that both the cytosolic free calcium concentration and the total cell calcium (free, bound to calcium-binding proteins, and stored in amorphous form) in the R cells strictly depend upon the molting cycle. Interestingly, the total cell calcium was higher (approximately 10 mmol l(-1)) in postmolt than in premolt (approximately 1 mmol l(-1)) and intermolt (approximately 0.3 mmol l(-1)). The calcium released from mitochondria was higher during premolt than during postmolt and intermolt, but the amount of calcium released from ATP-sensitive calcium stores was similar during all four stages. All together, our results suggest that the mitochondria-ATP-sensitive calcium stores system does not play a key role in calcium storage during the molting cycle but that it is involved in transcellular calcium flux. We hypothesize that lysosome or membrane-clad concretion vacuoles could represent the main site of calcium storage in hepatopancreatic R cells.

Transepithelial transport of zinc and L-histidine across perfused intestine of American lobster, Homarus americanus

The intestine of the American lobster, Homarus americanus, was isolated and perfused in vitro with a physiological saline, based on the ion composition of the blood, to characterize the mechanisms responsible for transmural transport of zinc and how the amino acid, L-histidine, affects the net movement of the metal across the tissue. Previous studies with this preparation, focusing on the characteristics of unidirectional mucosa to serosa (M to S) fluxes of (65)Zn(2+) and (3)H-L-histidine, indicated the presence of a brush border co-transport process responsible for simultaneously transferring the metal and amino acid across this tissue as an apparent bis-complex (Zn-[His](2)) using a PEPT-1-like dipeptide carrier mechanism. In addition, both zinc and L-histidine were also transferred toward the blood by separate transporters that were independent of the other substrate. The focus of the present study was to characterize the serosa to mucosa (S to M) flux of (65)Zn(2+) under a variety of conditions, and use these values in conjunction with those from the previous study, to assess the direction and magnitude of net metal movement across the tissue. Transmural S to M transport of (65)Zn(2+) was markedly reduced with the addition of the serosal inhibitors ouabain (32%), excess K(+) (25%), excess Ca(2+) (30%), Cu(2+) (38%), nifedipine (21%), and vanadate (53%). In contrast, this flux was markedly stimulated with the serosal addition of ATP (24%) and excess Na(+) (28%). These results suggest that S to M fluxes of zinc occurred by the combination of the basolateral Na/Ca exchanger (NCX), where zinc replaced calcium, and a basolateral nifedipine-sensitive calcium channel. Transmural M to S (65)Zn(2+) fluxes (5-100 microM) were threefold greater than S to M metal transport, and the addition of luminal L-histidine doubled the net M to S zinc flux over its rate in the absence of the amino acid. The results of this paper and those in its predecessor indicate that zinc transport by the lobster intestine is absorptive and significantly enhanced by luminal amino acids.

65Zn2+ Transport by lobster hepatopancreatic lysosomal membrane vesicles

In crustaceans, the hepatopancreas is the major organ system responsible for heavy metal detoxification, and within this structure the lysosomes and the endoplasmic reticulum are two organelles that regulate cytoplasmic metal concentrations by selective sequestration processes. This study characterized the transport processes responsible for zinc uptake into hepatopancreatic lysosomal membrane vesicles (LMV) and the interactions between the transport of this metal and those of calcium, copper, and cadmium in the same preparation. Standard centrifugation methods were used to prepare purified hepatopancreatic LMV and a rapid filtration procedure, to quantify 65Zn2+ transfer across this organellar membrane. LMV were osmotically reactive and exhibited a time course of uptake that was linear for 15-30 sec and approached equilibrium by 300 sec. 65Zn2+ influx was a hyperbolic function of external zinc concentration and followed Michaelis-Menten kinetics for carrier transport (Km = 32.3 +/- 10.8 microM; Jmax = 20.7 +/- 2.6 pmol/mg protein x sec). This carrier transport was stimulated by the addition of 1 mM ATP (Km = 35.89 +/- 10.58 microM; Jmax = 31.94+/-3.72 pmol/mg protein/sec) and replaced by an apparent slow diffusional process by the simultaneous presence of 1 mM ATP+250 microM vanadate. Thapsigargin (10 microM) was also a significant inhibitor of zinc influx (Km = 72.87 +/- 42.75 microM; Jmax =22.86 +/- 4.03 pmol/mg protein/sec), but not as effective in this regard as was vanadate. Using Dixon analysis, cadmium and copper were shown to be competitive inhibitors of lysosomal membrane vesicle 65Zn2+ influx by the ATP-dependent transport process (cadmium Ki = 68.1 +/- 3.2 microM; copper Ki = 32.7 +/- 1.9 microM). In the absence of ATP, an outwardly directed H+ gradient stimulated 65Zn2+ uptake, while a proton gradient in the opposite direction inhibited metal influx. The present investigation showed that 65Zn2+ was transported by hepatopancreatic lysosomal vesicles by ATP-dependent, vanadate-, thapsigargin-, and divalent cation-inhibited, carrier processes that illustrated Michaelis-Menten influx kinetics and was stimulated by an outwardly directed proton gradient. These transport properties as a whole suggest that this transporter may be a lysosomal isoform of the ER Sarco-Endoplasmic Reticulum Calcium ATPase.

Physiological characterization of 45Ca2+ and 65Zn2+ transport by lobster hepatopancreatic endoplasmic reticulum

The crustacean hepatopancreas is an epithelial-lined, multifunctional organ that, among other activities, regulates the flow of calcium into and out of the animal's body throughout the life cycle. Transepithelial calcium flow across this epithelial cell layer occurs by the combination of calcium channels and cation exchangers at the apical pole of the cell and by an ATP-dependent, calcium ATPase in conjunction with a calcium channel and an Na+/Ca2+ antiporter in the basolateral cell region. The roles of intracellular organelles such as mitochondria, lysosomes, and endoplasmic reticulum (ER) in transepithelial calcium transport or in transient calcium sequestration are unclear, but may be involved in transferring cytosolic calcium from one cell pole to the other. The ER membrane has a complement of ATP-dependent calcium ATPases (SERCA) and calcium channels that regulate the uptake and possible transfer of calcium through this organelle during periods of intense calcium fluxes across the epithelium as a whole. This investigation characterized the mechanisms of calcium transport by lobster hepatopancreatic ER vesicles and the effects of drugs and heavy metals on them. Kinetic constants for 45Ca2+ influx under control conditions were K(n) (m)=10.38+/-1.01 microM, J(max)=14.75+/-1.27 pmol/mg protein x sec, and n=2.53+/-0.46. The Hill coefficient for 45Ca2+ influx under control conditions, approximating 2, suggests that approximately two calcium ions were transported for each transport cycle in the absence of ATP or the inhibitors. Addition of 1 mM ATP to the incubation medium significantly (P<0.01) elevated the rate of 45Ca2+ influx at all calcium activities used and retained the sigmoidal nature of the transport relationship. The kinetic constants for 45Ca2+ influx in the presence of 1 mM ATP were K(n) (m)=12.76+/-0.91 microM, J(max)=25.46+/-1.45 pmol/mg protein x sec, and n=1.95+/-0.15. Kinetic analyses of ER 65Zn2+ influx resulted in a sigmoidal relationship between transport rate and zinc activity under control conditions (K(n) (m)=38.63+/-0.52 microM, J(max)=19.35+/-0.17 pmol/mg protein x sec, n=1.81+/-0.03). The Addition of 1 mM ATP enhanced 65Zn2+ influx at each zinc activity, but maintained the overall sigmoidal nature of the kinetic relationship. The kinetic constants for zinc influx in the presence of 1 mM ATP were K(n) (m)=34.59+/-2.31 microM, J(max)=26.09+/-1.17 pmol/mg protein x sec, and n=1.96+/-0.17. Both sigmoidal and ATP-dependent calcium and zinc influxes by ER vesicles were reduced in the presence of thapsigargin and vanadate. This investigation found that lobster hepatopancreatic ER exhibited a thapsigargin- and vanadate-inhibited, SERCA-like, calcium ATPase. This transporter displayed cooperative calcium transport kinetics (Hill coefficient, n approximately 2.0) and was inhibited by the heavy metals zinc and copper, suggesting that the metals may reduce the binding and transport of calcium when they are present in the cytosol.

Association between cadmium and calcium uptake and distribution during the moult cycle of female shore crabs, Carcinus maenas: an in vivo study

Net influxes into the haemolymph and tissue distribution of 45Ca and 109Cd were studied in vivo in female Carcinus maenas at different moult stages. Net influxes of 45Ca and 109Cd from water were higher in postmoult (A and B) C. maenas than in C3- and C4-intermoult crabs and the net influx of calcium was higher in C3-intermoult crabs than in C4-intermoult crabs. The net influxes of 45Ca and 109Cd increased in postmoult C. maenas with decreasing external calcium concentrations at constant salinity. At all external calcium concentrations a significant correlation existed between 45Ca and 109Cd accumulated in the haemolymph of individual animals. In vivo exposure of postmoult C. maenas to external lanthanum decreased the 45Ca and 109Cd uptake rates to 30 and 10%, respectively, of the control values. About 30% of injected 109Cd were found in the midgut gland, 10-20% in the gills and only a few (1-2) percent was lost to the seawater 24 h after injection. No major variations in tissue distribution of 109Cd were observed between moult stages in these tissues. Premoult crabs retained more cadmium in the haemolymph 24 h after injection than other moult stages, and postmoult crabs retained more in muscle. Between 20 and 40% of the injected 45Ca were excreted to the water, while only a few percent of the injected 45Ca were found in the soft tissues 24 h after injection. Large moult stage variations, however, were observed in the tissue distribution of internalised 45Ca. This study demonstrates that cadmium and calcium uptakes are elevated in postmoult C. maenas. The results indicate that cadmium and calcium in this stage are taken up via Ca2+-channels located in the apical membrane of gill epithelium cells. When internalised, however, cadmium and calcium are metabolised in fundamentally different ways, determined by the chemical properties and biological significance of the two metals.

In vivo and in vitro cadmium accumulation during the moult cycle of the male shore crab Carcinus maenas--interaction with calcium metabolism

The effect of moult stage on cadmium accumulation and distribution was investigated in vivo in male shore crabs Carcinus maenas exposed to 1 mg Cd l(-1) for 7 days. The accumulation of cadmium in all tissues examined was markedly higher in postmoult (A(1-2) and B(1-2)) compared to intermoult (C1, C3 and C4) and premoult (D(0-3)). In addition, elevated levels of cadmium were found in gills of late premoult (D(2-3)) animals. The total amount of cadmium accumulated in the tissues (haemolymph, gills, midgut gland and muscle) increased from 43 microg Cd in early premoult (D(0-1)) to 391 microg Cd in late postmoult (B(1-2)). Gills and midgut gland were the primary cadmium accumulating tissues in C4-intermoult and premoult (D(0-3)); in early postmoult (A(1-2)) haemolymph and midgut gland were the main cadmium containing tissues, while midgut gland dominated in late postmoult (B(1-2)) and early intermoult (C1 and C3). A detailed account of calcium distribution in haemolymph, gills, midgut gland, muscle and exoskeleton during the moult cycle is presented. Mechanistic links between cadmium and calcium uptake in posterior gills of C4-intermoult and early postmoult (A(1-2)) crabs were explored using an in vitro gill perfusion technique. Calcium and cadmium influxes were markedly higher in postmoult compared to intermoult. No differences between intermoult and postmoult effluxes were found for either calcium or cadmium. From intermoult to postmoult net influx increased from 2.4 to 29 micromol Ca2+ g(-1) ww(gill) h(-1) and from 0.24 to 25 nmol Cd2+ g(-1) ww(gill) h(-1). The results indicate that the postmoult increase in cadmium influx is due to increased active transport of cadmium, at least partly, by accidental uptake via calcium transporting proteins. The in vitro net influx rates corresponded accurately to the observed in vivo accumulation of both cadmium and calcium. Although cadmium accumulation and distribution are clearly linked to changes in calcium requirements, cadmium did not interfere with calcium accumulation or distribution at any stage during the moult cycle.

Physiological characterisation of a pH- and calcium-dependent sodium uptake mechanism in the freshwater crustacean,Daphnia magna

Daphnia are highly sensitive to sodium metabolism disruption caused by aquatic acidification and ionoregulatory toxicants, due to their finely balanced ion homeostasis. Nine different water chemistries of varying pH (4, 6 and 8) and calcium concentration (0, 0.5 and 1 mmol l–1) were used to delineate the mechanism of sodium influx in Daphnia magna. Lowering water pH severely inhibited sodium influx when calcium concentration was high, but transport kinetic analysis revealed a stimulated sodium influx capacity (Jmax) when calcium was absent. At low pH increasing water calcium levels decreased Jmax and raised Km (decreased sodium influx affinity), while at high pH the opposite pattern was observed (elevated Jmax and reduced Km). These effects on sodium influx were mirrored by changes in whole body sodium levels. Further examination of the effect of calcium on sodium influx showed a severe inhibition of sodium uptake by 100 μmol l–1 calcium gluconate at both low (50 μmol l–1) and high (1000 μmol l–1) sodium concentrations. At high sodium concentrations,stimulated sodium influx was noted with elevated calcium levels. These results, in addition to data showing amiloride inhibition of sodium influx(Ki=180 μmol l–1), suggest a mechanism of sodium influx in Daphnia magna that involves the electrogenic 2Na+/1H+ exchanger.

Accurate determination of Cd, Cr, Cu and Ni in woodlice and their skins--is moulting a means of detoxification?

Cd, Cr, Cu and Ni were determined in two different species of woodlice: Porcellio scaber and Porcellio dilatatus. Both P. scaber and P. dilatatus were cultivated under standardized conditions in a climatic chamber. Moreover, skins of the cultivated animals were collected and analysed separately to examine whether moulting is a way of detoxification from these elements. After drying and grinding both animal and skin samples, they were pooled to obtain enough sample material for each species. The pooled samples were digested in pure concentrated nitric acid using microwave-assisted high pressure digestion and, finally, analysed by ICP-OES. Special emphasis was given to quality control. To match the matrix of the samples very closely, the reference materials Dorm-2, Dogfish Muscle (Squalus acanthias) and SRM 1577b Bovine Liver were used to evaluate the whole analytical process including sample digestion. Analyses of the elements in the reference materials were carried out using three different wavelengths for each element simultaneously to check for spectral interferences and to select the wavelengths which were best suited for the analyses. Concentrations of Cd, Cr, Cu and Ni in woodlice and their skins indicated that moulting is a possible means of detoxification in the case of Cr and Ni.

65Zn2+ transport by lobster hepato-pancreatic baso-lateral membrane vesicles

The lobster (Homarus americanus) hepato-pancreatic epithelial baso-lateral cell membrane possesses three transport proteins that transfer calcium between the cytoplasm and hemolymph: an ATP-dependent calcium ATPase, a sodium-calcium exchanger, and a verapamil-sensitive cation channel. We used standard centrifugation methods to prepare purified hepato-pancreatic baso-lateral membrane vesicles and a rapid filtration procedure to investigate whether (65)Zn(2+) transfer across this epithelial cell border occurs by any of these previously described transporters for calcium. Baso-lateral membrane vesicles were osmotically reactive and exhibited a time course of uptake that was linear for 10-15 s and approached equilibrium by 120 s. In the absence of sodium, (65)Zn(2+) influx was a hyperbolic function of external zinc concentration and followed the Michaelis-Menten equation for carrier transport. This carrier transport was stimulated by the addition of 150 microM ATP (increase in K(m) and J(max)) and inhibited by the simultaneous presence of 150 micromol l(-1) ATP+250 micromol l(-1) vanadate (decrease in both K(m) and J(max)). In the absence of ATP, (65)Zn(2+) influx was a sigmoidal function of preloaded vesicular sodium concentration (0, 5, 10, 20, 30, 45, and 75 mmol l(-1)) and exhibited a Hill Coefficient of 4.03+/-1.14, consistent with the exchange of 3 Na(+)/1Zn(2+). Using Dixon analysis, calcium was shown to be a competitive inhibitor of baso-lateral membrane vesicle (65)Zn(2+) influx by both the ATP-dependent (K(i)=205 nmol l(-1) Ca(2+)) and sodium-dependent (K(i)=2.47 micromol l(-1) Ca(2+)) transport processes. These results suggest that zinc transport across the lobster hepato-pancreatic baso-lateral membrane largely occurred by the ATP-dependent calcium ATPase and sodium-calcium exchanger carrier proteins.