title: Extracellular digestion during hyposaline exposure in the Dungeness crab, Cancer magister, and the blue crab, Callinectes sapidus.
abstract: Extracellular digestive processes were examined in the Dungeness crab, Cancer magister and the blue crab, Callinectes sapidus, during hyposaline exposure. Both species are found in estuaries as adults, but vary in their ability to balance the cardiovascular and respiratory demands of concurrent osmoregulation and digestion. The weak osmoregulator, C. magister, is unable to balance the demands of osmoregulation and digestion. Concordant with observed decreases in oxygen consumption and mechanical digestion, proteolytic digestion within the foregut and hepatopancreas was delayed, resulting in a relative reduction of circulating amino acids post-feeding in low salinity. In contrast, the efficient osmoregulator, C. sapidus, balances the demands of osmoregulation and digestion, and mechanical digestion continues unabated in low salinity. Protease activity in the gut fluid and hepatopancreas showed either no change or a reduction over time. The transport of amino acids into the cells post-feeding is opposed by an efflux of amino acids at the cellular level, and resulted in a build up of amino acids in the hemolymph. Despite differences in the extracellular responses to low salinity exposure following feeding, both species were able to maintain high digestive efficiencies.
authors.affiliation: School of Life Sciences, University of Nevada, Las Vegas, 4505 Maryland Parkway, Las Vegas, Nevada, 89154, USA; Bamfield Marine Sciences Centre, Bamfield, British Columbia, V0R 1B0, Canada. Electronic address: Dan.Curtis@dfo-mpo.gc.ca.
authors.forename: Daniel L
authors.initials: DL
authors.lastname: Curtis
authors.forename: Frank
authors.initials: F
authors.lastname: van Breukelen
authors.forename: Iain J
authors.initials: IJ
authors.lastname: McGaw
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D000821:Animal Feed; D000818:Animals; D003386:Brachyura / Q000502:physiology*; D004063:Digestion; D041981:Gastrointestinal Tract / Q000378:metabolism; D006458:Hemolymph / Q000502:physiology; D043143:Hepatopancreas / Q000378:metabolism; D008297:Male; D064587:Osmoregulation; D010447:Peptide Hydrolases / Q000378:metabolism; D054712:Salinity
chemical_list: D000596:Amino Acids; D010447:Peptide Hydrolases
keywords: Amino acids; Crab; Digestive enzymes; Extracellular digestion; Osmoregulation; Protein synthesis