Osmotic challenge and expression of aquaporin 3 and Na/K ATPase genes in bovine embryos produced in vitro.

The aim of this study was to evaluate the effect of culture media and stage of development in the osmotic ability of in vitro-fertilized bovine embryos and the expression of aquaporin 3 (Aqp3) and Na/K ATPase isoform 1 (ATPAse1) genes in embryos (i) with different ability to undergo rehydration and (ii) following vitrification. In experiment 1, in vitro fertilized presumptive zygotes were co-cultured in SOFaac or modified CR2aa medium and embryos at blastocyst and expanded blastocyst stages at day 7 post-insemination were exposed to NaCl hypertonic medium (900 mOsm) for 5 min following 120 min of culture in isotonic medium in order to evaluate dehydration and rehydration, respectively. No difference (P>0.05) on blastocyst rate was found between CR2aa and SOFaac medium but embryos co-cultured in SOFaac medium underwent greater (P<0.05) dehydration. Embryos at expanded blastocyst stage underwent greater dehydration but slower rehydration than embryos at blastocysts stage (P<0.05). In the experiment 2, the amount of Aqp3 and ATPase1 transcripts were quantified in blastocysts with high or low rehydration after exposure to hypertonic medium. No difference (P>0.05) on relative amount of transcripts was found in either genes. In the experiment 3, expanded blastocysts produced in a co-culture system were vitrified, warmed and then cultured for 72 h for analysis of embryo survival and amount of Aqp3 and ATPase1 transcripts. Lower (P<0.05) embryo survival rate was found for vitrified-warmed embryos (57.9%) than for their fresh counterparts (84.6%). There was no difference on expression of ATPase1 gene but lower (P<0.01) amount of Aqp3 transcripts was found in the vitrified-warmed embryos. In conclusion, embryo ability to undergo shrinkage and swelling is influenced by medium used in a co-culture system and by embryo stage. Rehydrating ability of embryos after exposure to NaCl hypertonic medium is not associated with variations on expression of Aqp3 and ATPase1 genes, but the vitrification can alter gene expression of in vitro-fertilized bovine embryos produced in a co-culture system.