The crustacean gill is a multi-functional organ, and it is the site of a number of physiological processes, including ion transport, which is the basis for hemolymph osmoregulation; acid-base balance; and ammonia excretion. The gill is also the site by which many toxic metals are taken up by aquatic crustaceans, and thus it plays an important role in the toxicology of these species. This review provides a comprehensive overview of the ecology, physiology, biochemistry, and molecular biology of the mechanisms of osmotic and ionic regulation performed by the gill. The current concepts of the mechanisms of ion transport, the structural, biochemical, and molecular bases of systemic physiology, and the history of their development are discussed. The relationship between branchial ion transport and hemolymph acid-base regulation is also treated. In addition, the mechanisms of ammonia transport and excretion across the gill are discussed. And finally, the toxicology of heavy metal accumulation via the gill is reviewed in detail.

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Carcinus maenas, commonly known as the European green crab, is one of the best-known and most successful marine invasive species. While a variety of natural and anthropogenic mechanisms are responsible for the geographic spread of this crab, its ability to adapt physiologically to a broad range of salinities, temperatures and other environmental factors has enabled successful establishment in these new habitats. To extend our understanding of hormonal control in C. maenas, including factors that allow for its extreme adaptability, we have undertaken a mass spectral/functional genomics investigation of the neuropeptides used by this organism. Via a strategy combining MALDI-based high resolution mass profiling, biochemical derivatization, and nanoscale separation coupled to tandem mass spectrometric sequencing, 122 peptide paracrines/hormones were identified from the C. maenas central nervous system and neuroendocrine organs. These peptides include 31 previously described Carcinus neuropeptides (e.g. NSELINSILGLPKVMNDAamide [β-pigment dispersing hormone] and PFCNAFTGCamide [crustacean cardioactive peptide]), 49 peptides only described in species other than the green crab (e.g. pQTFQYSRGWTNamide [Arg 7 -corazonin]), and 42 new peptides de novo sequenced here for the first time (e.g. the pyrokinins TSFAFSPRLamide and DTGFAFSPRLamide). Of particular note are a collection of 25 FMRFamide-like peptides (including 9 new isoforms sequenced de novo) and a collection of 25 A-type allatostatin peptides (including 10 new sequences reported for the first time) in this study. Both peptide families are among the most diverse families, each containing a large number of isoforms in arthropod species. Also of interest was the identification of two SIFamide isoforms, GYRKPPFNGSIFamide and VYRKPPFNGSIFamide, the latter peptide known previously only from members of the astacidean genus Homarus. Using transcriptome analyses, 15 additional peptides were characterized, including an isoform of bursicon β and a neuroparsin-like peptide. Collectively, the data presented in this study * Correspondence to: Dr. Lingjun Li, School of Pharmacy, University of Wisconsin, 777 Highland Avenue, Madison, Wisconsin 53705-2222 USA; Phone: 608-265-8491; Fax: 608-262-5345; lli@pharmacy.wisc.edu. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. not only greatly expand the number of identified C. maenas neuropeptides, but also provide a framework for future investigations of the physiological roles played by these molecules in this highly adaptable species. NIH Public Access KeywordsCarcinus maenas; European green cr...

Carbonic anhydrase (CA) is a central enzyme to both transport and metabolic processes at the cellular level. In metabolically active tissue such as muscle, CA in the cytoplasm and on the sarcolemma appears to be important in facilitating CO2 transport out of the cell. Membrane-associated CA, with an extracellular orientation, also appears to be important in acidifying the outer boundary layer through the catalyzed hydration of excreted CO2. This facilitates cellular ammonia transport by providing H+ ions for the protonation of NH3, thus maintaining the trans-membrane NH3 gradient. Mitochondrial CA is known to supply HCO3- for the initial reactions of gluconeogenesis and ureagenesis in mammalian tissues, but systematic comparative studies of CA as a metabolic enzyme are lacking. CA probably evolved as an enzyme of trans-membrane facilitated CO2 transport and took on a secondary metabolic role later in metazoan evolution.

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