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Betaine is a highly effective organic osmolyte but does not appear to be transported by established organic osmolyte transporters in mouse embryos
Author(s) -
Hammer MaryAnne,
Baltz Jay M.
Publication year - 2002
Publication title -
molecular reproduction and development
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.745
H-Index - 105
eISSN - 1098-2795
pISSN - 1040-452X
DOI - 10.1002/mrd.10088
Subject(s) - betaine , osmolyte , transporter , biology , embryo , biochemistry , glycine , membrane transport protein , osmotic concentration , amino acid , microbiology and biotechnology , gene
Betaine protects early preimplantation mouse embryos against increased osmolarity in vitro, functioning as an organic osmolyte. Betaine is effective at very low external concentrations, with half‐maximal protection of 1‐cell embryo development to blastocysts at approximately 50 μM, making it one of the best osmoprotectants for mouse preimplantation embryos. We performed studies designed to determine whether known high‐affinity organic osmolyte transporters could account for the ability of betaine to act as an organic osmolyte in preimplantation embryos. We found no evidence in 1‐cell embryos of transport by a betaine/GABA transporter (BGT1), the osmoregulated betaine transporter found in a number of cell types, as betaine and GABA did not inhibit each other's transport. Instead, all saturable GABA transport in embryos was apparently via the β‐amino acid transporter. We also found that the glycine transporter, GLY, which mediates osmoprotective transport of glycine in early preimplantation embryos, does not appear to transport betaine. Finally, increased osmolarity did not induce any detectable System A amino acid transporter activity, which is osmotically‐inducible in other cells and can transport betaine. There does appear, however, to be a saturable betaine transporter in 1‐cell mouse embryos, as considerable 14 C‐betaine transport was measured which was substantially inhibited by excess unlabeled betaine. Our data imply that betaine functions as an organic osmolyte in embryos due to its saturable transport via a mechanism distinct from known osmolyte transporters. We propose that an unidentified high‐affinity betaine transporter may be expressed in early embryos and mediate transport of betaine as an organic osmolyte. Mol. Reprod. Dev. 62: 195–202, 2002. © 2002 Wiley‐Liss, Inc.