Permeability of the vitelline membrane of zebrafish (Brachydanio rerio) embryos to methanol and propane-1,2-diol

Permeability of the vitelline membrane of gastrula (7-h) stage zebrafish (Brachydanio rerio) embryos to water and the cryoprotectants methanol and propan-1,2-diol at 22 degrees C was studied. Volumetric changes of the embryos during cryoprotectant exposure were analysed using real time video microscopy. The Boyle Van't Hoff relationship was determined using sucrose as a non-permeating compound. Equilibrium volumetric behaviour of the embryos indicated that they behaved as nearly ideal osmometers over the rage of 250-1800 mOsm, and the osmotically inactive volume of the embryos was 80.6%. The Kedem-Katchalsky (K-K) parameters of water permeability (Lp), cryoprotectant permeability to) and reflection coefficient (sigma) were determined using DIFFCHAM software. The mean values of the parameters are: Lp = 0.17 and 0.10 (mu m/min*atm); omega = 0.16 and 0.05 (mu m/sec) and sigma = 0.84 and 0.63 when embryos are exposed to methanol and propan-1,2-diol respectively. Lp values in this present study for gastrula stage embryos fall in between the values reported previously for zebrafish ovarian egg and shed, non-developing egg. As far as we aware, the omega and sigma values for methanol and propan-1,2-diol are the first values reported for the vitelline membrane of fish embryos.