Functional polarity of the tentacle of the sea anemone Anemonia viridis: role in inorganic carbon acquisition

Am J Physiol. 1998 Feb;274(2):R303-10. doi: 10.1152/ajpregu.1998.274.2.R303.


The oral epithelial layers of anthozoans have a polarized morphology: photosynthetic endosymbionts live within endodermal cells facing the coelenteric cavity and are separated from the external seawater by the ectodermal layer and the mesoglea. To study if this morphology plays a role in the supply of inorganic carbon for symbiont photosynthesis, we measured the change in pH and the rate of OH- (H+) fluxes induced by each cell layer on a tentacle of the sea anemone Anemonia viridis. Light-induced pH increase of the medium bathing the endodermal layers led to the generation of a transepithelial pH gradient of approximately 0.8 pH units across the tentacle, whereas darkness induced acidification of this medium. The light-induced pH change was associated with an increase of total alkalinity. Only the endodermal layer was able to induce a net OH- secretion (H+ absorption). The light-induced OH- secretion by the endodermal cell layer was dependent on the presence of HCO3- in the compartment facing the ectoderm and was sensitive to several inhibitors of ion transport. [14C] HCO3- incorporation into photosynthates confirmed the ectodermal supply, the extent of which varied from 25 to > 90%, according to HCO3- availability. Our results suggest that the light-induced OH- secretion by the endodermal cell layer followed the polarized transport of HCO3- and its subsequent decarboxylation within the endodermal cell layer. This polarity may play a significant role both in inorganic carbon absorption and in the control of light-enhanced calcification in scleractinian corals.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amiloride / pharmacology
  • Animals
  • Bicarbonates / metabolism
  • Carbon / metabolism*
  • Endoderm / metabolism
  • Hydrogen-Ion Concentration
  • Hydroxides / metabolism
  • Kinetics
  • Light
  • Oxygen / metabolism
  • Photosynthesis
  • Sea Anemones / anatomy & histology*
  • Sea Anemones / metabolism*
  • Sodium / pharmacology


  • Bicarbonates
  • Hydroxides
  • Carbon
  • Amiloride
  • Sodium
  • Oxygen