The Fertilization Potential Provides a Fast Block to Polyspermy in Lamprey Eggs

[摘要] Atfertilization,themembranepotentialoftheeggofthelamprey,Lampetrajaponica,shiftedrapidlyfromitsrestingvalueof-12to+36mVandgraduallyreturnedtoaboutthesamerestinglevel(fertilizationpotential).TheamplitudeofdepolarizationwasinfluencedbytheexternalCl-concentrationandbyanunionchannelblocker,DIDS,indicatingthatthepositiveshiftofmembranepotentialresultedfromCl-efflux.Asimilarchangeinmembranepotential(activationpotential)wasobservedwhentheunfertilizedeggwasprickedwithafineneedleortreatedwithA23187toinduceparthenogeneticactivation.Prickingattheanimalpoleregion(predeterminedsiteforspermentry)resultedintheoccurrenceofanimmediateactivationpotentialandtheinitiationofcorticalgranuleexocytosis.Atimelagbetweentheprickingandtheoccurrenceoftheactivationpotentialwasobservedwhentheeggwasprickedatadistancefromtheanimalpole.Inthisinstance,theactivationpotentialwasproducedimmediatelybeforethepropagatingcorticalgranuleexocytosisinitiatedattheprickedsitereachedtheanimalpoleregion.Sperm-eggfusionwasblockedineggsvoltage-clampedat+20to+40mVandinseminated,whereasittookplaceineggsclampedat-60to0mV.However,mosteggsclampedat+20to+40mVdidactivate,indicatingthatthevoltagedependenceofeggactivationdiffersfromthatofsperm-eggfusion.Althougheggsvoltage-clampedatnegativemembranepotentialspermittedmultiplespermtofusewiththeeggplasmamembrane,thenucleusofthefusedspermdidnotnecessarilyentertheooplasm.Weconcludethat:(1)Afastelectricalblockagainstpolyspermyoperatesinthisspeciesandiseffectiveforabout160secoftheonsetofthepositiveshift;(2)theopeningofCl-channelsisresponsibleforthepotentialchange;(3)thechannelsarelargelylocalizedintheanimalpoleregion;(4)duringvoltageclampatpositivepotentials,eggscanbeactivatedwithoutsperm-eggfusion;and(5)duringvoltageclampatnegativepotentials,sperm-eggfusionoccurs,butspermentryintotheeggcytoplasmdoesnotalwaysproceed.

[学科分类] 生物科学（综合）