PERMEABILITY OF DECHORIONATED ONE-CELL AND 6-SOMITE STAGE ZEBRAFISH (BRACHYDANIO-RERIO) EMBRYOS TO WATER AND METHANOL

The permeability of dechorionated one-cell and six-somite stage zebraf ish (Brachydanio rerio) embryos to water and the cryoprotectant methan ol at 22 degrees C was studied, using real-time video microscopy to de termine the volumetric changes of the embryos during cryoprotectant ex posure. The equilibrium volumetric behavior of the embryos and the Boy le-van't Hoff relationships were determined using sucrose as a nonperm eating compound. These showed the embryos to behave as nearly ideal os mometers over the range of 253-1724 mOsm, with osmotically inactive vo lumes of 72.9 and 82.6% for one-cell and six-somite stage embryos, res pectively. The Boyle-van't Hoff relationship of the ovary eggs was als o determined for comparison and their osmotically inactive volume was 63.9%, The Kedem-Katchalsky parameters of water permeability (L-p), cr yoprotectant permeability (P-s), and reflection coefficient (sigma) we re determined using DIFFCHAM software. The parameters reported in this study are phenomenological parameters referring to the overall embryo response. The mean values of these parameters were L-p = 0.34 and 0.3 5 (mu m/minatm), P-s = 0.45 and 0.04 (mu m/s), and sigma = 0.88 and 0 .93 for one-cell and six-somite stage embryos, respectively. While the water permeability of the dechorionated zebrafish embryos at differen t developmental stages remained relatively stable, the permeability to the cryoprotectant methanol (P-s) appeared to decrease during embryo development. The P-s and sigma values for methanol are the first repor ted for dechorionated fish embryos at these stages, (C) 1998 Academic Press.