Molecular characterization of V-type H(+)-ATPase (B-subunit) in gills of euryhaline crabs and its physiological role in osmoregulatory ion uptake.
The vacuolar-type H(+)-ATPase (V-ATPase) has been implicated in osmoregulatory ion uptake across external epithelia of a growing variety of species adapted to life in fresh water. In the present study, we investigated whether the V-ATPase may also function in a euryhaline species that tolerates brackish water (8 salinity) but not fresh water, the shore crab Carcinus maenas. cDNA coding for the regulatory B-subunit of the V-ATPase was amplified and sequenced from C. maenas gills and partially sequenced from four other crab species. Two isoforms differing in the 3'-untranslated region were found in C. maenas. In this species, the abundance of B-subunit mRNA was greater in the respiratory anterior gills than the ion-transporting posterior gills and was not increased by acclimation to dilute salinity. Immunocytochemical analysis showed that the B-subunit protein is not targeted to the apical membrane but is distributed throughout the cytoplasmic compartment. Physiological studies of isolated perfused gills indicated that the V-ATPase inhibitor bafilomycin had no effect on transepithelial potential difference. Thus, in contrast to the freshwater-tolerant Chinese crab Eriocheir sinensis, in which the V-ATPase appears to play an important osmoregulatory role, the V-ATPase in C. maenas probably functions in acidification of intracellular organelles but not in transbranchial NaCl uptake.
Weihrauch
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D
Department of Biology, Lake Forest College, Lake Forest, IL 60045, USA.
Ziegler
A
A
Siebers
D
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Towle
D W
DW
D020413:3' Untranslated Regions; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003386:Brachyura / Q000201:enzymology*; D018076:DNA, Complementary / Q000737:chemistry; D015870:Gene Expression; D005880:Gills / Q000201:enzymology*; D006801:Humans; D007150:Immunohistochemistry; D008969:Molecular Sequence Data; D009994:Osmolar Concentration; D016133:Polymerase Chain Reaction; D006180:Proton-Translocating ATPases / Q000737:chemistry / Q000235:genetics* / Q000502:physiology*; D016415:Sequence Alignment; D012965:Sodium Chloride; D025262:Vacuolar Proton-Translocating ATPases; D014882:Water-Electrolyte Balance / Q000502:physiology*
D020413:3' Untranslated Regions; D018076:DNA, Complementary; D012965:Sodium Chloride; D025262:Vacuolar Proton-Translocating ATPases; D006180:Proton-Translocating ATPases