The ionic composition of the hydrothermal vent tube worm Riftia pachyptila: Evidence for the elimination of SO42- and H+ and for a Cl-/HCO3- shift

Riftia pachyptila is one of the most specialized invertebrate hosts of chem oautotrophic symbionts. Crucial to the functioning of this symbiosis is how these worms cope with fluctuating ion concentrations. Internal sulfate lev els in R. pachyptila appear comparable with other benthic marine invertebra tes, despite the production of sulfate internally by means of the bacterial oxidation of hydrogen sulfide, suggesting that these worms are able to eli minate sulfate effectively Internal chloride levers appear comparable; howe ver, coelomic fluid chloride levels decrease significantly as the amount of coelomic fluid bicarbonate increases, demonstrating a 1:1 stoichiometry. W e believe this shift in chloride, out of the body fluids, is needed to comp ensate for changes in electrochemical balance caused by the large increase (up to and greater than 60 mmol L-1) in negatively charged bicarbonate. Rif tia pachyptila fits the general pattern of monovalent ion concentrations th at is seen in other benthic marine invertebrates, with a high [Na+] : [K+] ratio extracellularly and low [Na+] : [K+] ratio intracellularly. Extracell ular pH values of 7.38 +/- 0.03 and 7.37 +/- 0.04 for coelomic fluid and va scular blood, respectively, as well as intracellular FH values of 7.37 +/- 0.04 and 7.04 +/- 0.05 for plume and trophosome tissue, respectively, were measured. On the basis of significant decreases in extracellular pH and, in some cases, Na+ and K+, in worms exposed to carbonyl cyanide m-chloropheny lhydrazone, sodium vanadate, and N-ethylmaleimide, we suggest that high con centrations of H+-ATPases, perhaps Na+/H+- or K+/H+-ATPases, are involved i n H+ elimination in these animals.