Activation of a Na+-dependent amino acid transport system in preimplantation mouse embryos☆

[摘要] Theuptakeofl-methionine-methyl-3Handl-leucine-3Hfromcompletelydefinedmediumintoacid-solublefractionsofpreimplantationmouseembryoshasbeenstudied.Latefour-cellembryosandearlyblastocystsraisedinvitrocanconcentratebothaminoacidsbyprocesseswhichexhibitsaturable,Michaelis-Mententypekinetics,characteristicofcarrier-mediatedactivetransportsystems.Thisuptakeistemperature-sensitiveandinhibitedbycertainaminoacidswhichcompeteforthesameuptakesites.Methionineuptakeseemstobemediatedbyasingletransportsystem(Km=6.25×10−5M)atthefour-cellstage.Complexkineticssuggestthattwodistincttransportsystemsexistattheearlyblastocyststage(Km=6.25×10−5M;8.9×10−4M).Vmaxvalues(mg/embryo/15min)formethionineandleucinetransportincreasesignificantlyfromthelatefour-cellstagetotheblastocyststage,suggestingthatadditionalcarriersareproducedoractivatedduringdevelopment.Mostimportantly,leucineandmethioninetransportisNa+-independentatthefour-cellstage,methioninetransportispartiallydependentatthemorulastage,andbothaminoacidsarecompletelyNa+-dependentattheblastocyststage.Thecumulativeresultssuggestthatpreimplantationembryosaccumulateleucineandmethioninebyspecific,chemicallymediated,activetransportsystems.Thequalitativeandquantitativedevelopmentalchangesincellmembranefunctionmayrepresentpreparatorystepsforsubsequentgrowthofembryonicand/ortrophoblasticcells.

[学科分类] 生物科学（综合）