title: Involvement of H(+)-ATPase and carbonic anhydrase in inorganic carbon uptake for endosymbiont photosynthesis.
abstract: Symbiotic cnidarians absorb inorganic carbon from seawater to supply intracellular dinoflagellates with CO(2) for their photosynthesis. To determine the mechanism of inorganic carbon transport by animal cells, we used plasma membrane vesicles prepared from ectodermal cells isolated from tentacles of the sea anemone, Anemonia viridis. H(14)CO(-)(3) uptake in the presence of an outward NaCl gradient or inward H(+) gradient, showed no evidence for a Cl(-)- or H(+)- driven HCO(-)(3) transport. H(14)CO(-)(3) and (36)Cl(-) uptakes were stimulated by a positive inside-membrane diffusion potential, suggesting the presence of HCO(-)(3) and Cl(-) conductances. A carbonic anhydrase (CA) activity was measured on plasma membrane (4%) and in the cytoplasm of the ectodermal cells (96%) and was sensitive to acetazolamide (IC(50) = 20 nM) and ethoxyzolamide (IC(50) = 2.5 nM). A strong DIDS-sensitive H(+)-ATPase activity was observed (IC(50) = 14 microM). This activity was also highly sensitive to vanadate and allyl isothiocyanate, two inhibitors of P-type H(+)-ATPases. Present data suggest that HCO(-)(3) absorption by ectodermal cells is carried out by H(+) secretion by H(+)-ATPase, resulting in the formation of carbonic acid in the surrounding seawater, which is quickly dehydrated into CO(2) by a membrane-bound CA. CO(2) then diffuses passively into the cell where it is hydrated in HCO(-)(3) by a cytosolic CA.
authors.affiliation: Observatoire Océanologique Européen, Centre Scientifique de Monaco, MC-98000 Monaco, Principality of Monaco.
authors.forename: P
authors.initials: P
authors.lastname: Furla
authors.forename: D
authors.initials: D
authors.lastname: Allemand
authors.forename: M N
authors.initials: MN
authors.lastname: Orsenigo
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D027321:Anion Transport Proteins; D001386:Azides / Q000494:pharmacology; D001639:Bicarbonates / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002244:Carbon / Q000493:pharmacokinetics*; D002250:Carbon Radioisotopes / Q000493:pharmacokinetics; D002256:Carbonic Anhydrases / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002712:Chlorides / Q000493:pharmacokinetics; D002713:Chlorine / Q000493:pharmacokinetics; D004475:Ectoderm / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D056890:Eukaryota / Q000201:enzymology; D006863:Hydrogen-Ion Concentration; D008564:Membrane Potentials / Q000502:physiology; D008871:Microvilli / Q000378:metabolism; D009579:Nitrobenzoates / Q000494:pharmacology; D009840:Oligomycins / Q000494:pharmacology; D009994:Osmolar Concentration; D010788:Photosynthesis / Q000502:physiology*; D006180:Proton-Translocating ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011522:Protons; D011868:Radioisotopes / Q000493:pharmacokinetics; D012287:Rickettsiaceae / Q000201:enzymology*; D012615:Sea Anemones / Q000378:metabolism*; D014638:Vanadates / Q000494:pharmacology; D062367:ortho-Aminobenzoates / Q000494:pharmacology
chemical_list: D027321:Anion Transport Proteins; D001386:Azides; D001639:Bicarbonates; D002250:Carbon Radioisotopes; D002712:Chlorides; D004791:Enzyme Inhibitors; D009579:Nitrobenzoates; D009840:Oligomycins; D011522:Protons; D011868:Radioisotopes; D062367:ortho-Aminobenzoates; C058176:5-nitro-2-(3-phenylpropylamino)benzoic acid; D014638:Vanadates; D002713:Chlorine; D002244:Carbon; C001209:fenamic acid; D000251:Adenosine Triphosphatases; C031652:anion-sensitive ATPases; D006180:Proton-Translocating ATPases; D002256:Carbonic Anhydrases; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid