The organic osmolytes betaine and proline are transported by a shared system in early preimplantation mouse embryos.
Betaine and proline protect preimplantation mouse embryos against increased osmolarity and decreased cell volume, implying that they may function as organic osmolytes. However, the transport system(s) that mediates their accumulation in fertilized eggs and early embryos was unknown, and previously identified mammalian organic osmolyte transporters could not account for their transport. Here, we report that there is a single saturable transport component shared by betaine and proline in 1-cell mouse embryos. A series of inhibitors had nearly identical effects on both betaine and proline transport by this system. In addition, K(i) values for reciprocal inhibition of betaine and proline transport were approximately 100-300 microM, similar to K(m) values ( approximately 200-300 microM) for their transport, and both had similar maximal transport rates (V(max)). The K(i) values for inhibition of betaine and proline transport by dimethylglycine were similar ( approximately 2 mM), further supporting transport of both substrates by a single transport system. Finally, betaine and proline transport each required Na(+)- and Cl(-). These data were consistent with a single, Na(+)- and Cl(-)-requiring, betaine/proline transport system in 1-cell mouse embryos. While betaine was only transported by a single saturable system, we found an additional, less conspicuous proline transport route that was betaine-insensitive, Na(+)-sensitive, and inhibited by alanine, leucine, cysteine, and methionine. Furthermore, we showed that betaine, like proline, is present in the mouse oviduct and thus could serve as a physiological substrate. Finally, accumulation of both betaine and proline increased with increasing osmolarity, consistent with a possible role as organic osmolytes in early embryos.
Anas
Mohamed-Kheir Idris
MK
Hormones, Growth and Development Program, Ottawa Health Research Institute, Ottawa, Ontario, Canada.
Hammer
Mary-Anne
MA
Lever
Michael
M
Stanton
Jo-Ann L
JA
Baltz
Jay M
JM
D000409:Alanine / Q000494:pharmacology; D000596:Amino Acids / Q000494:pharmacology; D000818:Animals; D001622:Betaine / Q000032:analysis / Q000378:metabolism* / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D001755:Blastocyst / Q000187:drug effects / Q000378:metabolism*; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D046149:Embryo Culture Techniques; D005187:Fallopian Tubes / Q000737:chemistry; D005260:Female; D007700:Kinetics; D051379:Mice; D011392:Proline / Q000378:metabolism* / Q000494:pharmacology; D012521:Sarcosine / Q000031:analogs & derivatives / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism; D013997:Time Factors; D014882:Water-Electrolyte Balance / Q000187:drug effects
D000596:Amino Acids; D002352:Carrier Proteins; D002712:Chlorides; D001622:Betaine; C025138:dimethylglycine; D011392:Proline; D012964:Sodium; D000409:Alanine; D012521:Sarcosine