IONIC MOVEMENTS ACROSS THE CHORION IN NEWLY SHED SALMON EGGS (SALMO-SALAR L)

Sodium and chloride exchange and trans-chorion potentials were investigated in newly shed eggs from Atlantic salmon. Exposure of eggs to pH 3.5 caused the non-labile sodium fraction at pH 7.0 to become labile and lost from the egg. Chloride fluxes appear unaffected by the pH of the external medium. Trans-chorion potential was inside negative (about -100 mV) in dilute media (10-5 mol·l-1 NaCl or KCl) and immediately decreased as external cation concentration was increased, by about 46 mV/decade change in cation concentration, reaching about 0 mV in 10-2 mol·l-1 cation. Return to dilute cation solutions resulted in a slow increase in potential (repolarisation) and the time course of these potential changes was paralleled by the rate of sodium efflux, although chloride efflux was very rapid. After exposure to acid conditions repolarisation of the egg on return to dilute cation concentrations was preceeded by a phase when the pvp became inside positive. The results are discussed in terms of chorion structure, anionic charge on the perivitelline molecules and unstirred layers within the chorion. © 1990 Springer-Verlag.