Water permeability of the oral epithelial layers of the sea anemone, Anemonia viridis

Abstract

Water permeability of the oral epithelial layers of the anthozoan Anemonia viridis was studied. We determined a diffusional water permeability of 17 × 10–5 cm s–1 and an osmotic water permeability of 2.5 10–5 cm s–1. These permeability coefficients were independent of the state of contraction of the tentacle. Compared to other tissues, water permeability in sea anemones is relatively low. This result is quite surprising, since we determined in a previous study that the ionic permeabilities of the oral epithelial layers of A. viridis were characteristic of a leaky tissue (Bénazet-Tambutté et al., '96a). The low water permeability of the oral epithelial layers of A. viridis can be considered as an adaptational mechanism for maintaining a hydrostatic skeleton. The ratio Po/Pd was about 14. The osmotic flow was symmetric whatever the direction of the gradient. Temperature did not affect diffusional water flux. The Arrhenius energy of activation for osmotic flux was about 5 kcal mol–1. Osmotic water flow was insensitive to mercury. Our results suggest the possible existence of HgCl2-insensitive water channels. J. Exp. Zool. 279:1–8, 1997.© 1997 Wiley-Liss, Inc.