Voltage clamp studies of fertilization in sea urchin eggs: II. Current patterns in relation to sperm entry, nonentry, and activation☆

摘要

Followingattachmentofaspermtothesurfaceofaseaurchineggclampedatamembranepotential(Vm)morepositivethan+17mV,nochangesinmembraneconductancecanbedetected,thespermdoesnotentertheegg,andnomorphologicalchangescanbedetected.AtVmfrom+17toa?’100mVthreecharacteristicallydifferenttypesofcurrentprofilesareobserved:TypeIareactivationcurrentsineggspenetratedbyasperm.Thesehavethreephases,whichoccurinalleggsclampedatVmfrom+17toa?’20mVandindecreasingpercentagesatclampedVmmorenegativethana?’20mV(toa?’75mV).Completefertilizationenvelopesareelevated,relativelylargemound-shapedfertilizationconesform,andtheeggsdeveloptonormalembryos.TypeIIarespermtransientcurrentsineggsnotpenetratedbyasperm,theeggsotherwiseremainingintheunfertilizedstate.ThesetransientsaresimplerandshorterthantypeIcurrents,andareobservedonlyatclampedVmmorenegativethana?’20mV.TypeIIIaremodifiedactivationcurrentsineggsnotpenetratedbyasperm.Thesehavethreephases,areobservedonlyatclampedVmmorenegativethana?’20mV,andaretheonlytypeofactivationcurrentseenatclampedVmmorenegativethana?’75mV.Completefertilizationenvelopesareelevated,thefertilizationconesaresmallandfilament-like,andtheeggsfailtocleave.Weconcludethat(a)thespermtransientcurrents(typeII)andphase1oftheactivationcurrents(typesIandIII)aresimilareventsgeneratedbyasperm-initiatedlocalizedconductanceincrease,(b)theabruptdecreaseofcurrentwhichterminatesthespermtransientsandphase1oftypeIIIcurrentsresultsfromaturnoffofthesperm-inducedconductanceincreaseandsignalsthatthespermwillnotentertheegg,and(c)theoccurrenceofphase2duringanelectrophysiologicalresponseinducedbyaspermindicatesthattheeggisactivating.