Developmental changes in membrane transport and permeability in the early mouse embryo☆

[摘要] Electrophysiologicalandisotopetracerfluxexperimentswereperformedtomeasurethemembraneionpermeabilityandtransportpropertiesofthetwo-cellmouseembryo.TheresultsshowthattheinternalexchangeableNaandKare151and130mM,respectively,andtheirmembranepermeabilitiesare(PNa)16×10−8cmsec−1and(PK)21×10−8cmsec−1.Thesevaluespredictamembranepotentialof−24mV(insidenegative)whichagreeswellwith−19mVmeasuredwithmicroelectrodes.Ouabain-sensitiveisotopefluxesdemonstrateaNa/Kpumpmechanismwithastoichiometryof1.7:1(Na:K).Anexternal-Na-dependentNaeffluxisdemonstratedbythereductionofunidirectionalNaeffluxinNa-freemedium,butthereisnoevidenceforasimilarmechanismofKeffluxatthisstageofdevelopment.Theseresultsarecomparedwiththevaluesreportedforthemouseoocyte[Powers,R.D.,andTupper,J.T.(1974).Develop.Biol.38,320–331;(1975).Exp.CellRes.91,413–421].Thehyperpolarizationofthemembranepotentialascomparedwiththeoocyte(−13mV)resultsprimarilyfromtheincreasedPKPNaratio.Asimilarphenomenonhasbeennotedinotherdevelopingembryos.Theincreaseinpump-mediatedKinfluxatthetwo-cellstageisaccompaniedbyadecreaseofsimilarmagnitudeintheexternal-K-dependentKeffluxwhichisfoundintheoocyte.ThissuggeststhattheKî—¸Kexchangemechanismmaybeconvertedtoanactivepump.Becauseofthechangesinionconcentrationsandmovementsandtheunusualmetabolicrequirementsofthemouseembryo,theeffectofexternalNaontheuptakeofglucoseandpyruvateintheoocyteandtwo-andeight-cellstagewasexamined.NoNa-dependentcarbohydratetransportcouldbefoundatthesestages.

[学科分类] 生物科学（综合）