Asymmetrical Diffusion of Sodium and Water through the Skin of Sea Snakes

Abstract

Diffusion of water, Na, Cl, and ethanol were studied in vitro across whole, fresh skins of six species of sea snakes placed between 1-M solute solutions and distilled water. Water influxes varied from 60 μmol/cm² · h in Pelamis to 240 μmol/cm² · h in Aipysurus laevis. In four species, including Pelamis and Aipysurus, influx exceeded effluix. This is a reversal of the flux asymmetry found in freshwater snakes measured under identical circumstances. Sodium and Cl fluxes across whole skins were low, with effluxes exceeding influxes in A. laevis. In shed skins of A. laevis, Na fluxes were considerably higher than in whole skins, but efflux exceeded influx by a factor of two to 16. In freshwater snakes, the reverse was true; ionic influxes exceeded effluxes. Thus the directions of asymmetrical diffusion of water and Na were opposite in marine and freshwater snakes. Since these asymmetries tend to slow the downhill diffusion of water and Na, they may be part of a previously unsuspected mechanism of osmoregulation residing in the integument.