A partial sequence of ionic changes associated with the acrosome reaction of Strongylocentrotus purpuratus☆

[摘要] RelationshipsamongseveraloftheionmovementsassociatedwiththeacrosomereactionofS.purpuratuswereinvestigated.Eggjellyinitiates45Ca2+and22Na+uptake,andK+andH+efflux.H+effluxand22Na+uptakeoccurwithapproximatelyequivalentstoichiometriesasrapidlyastheappearanceofacrosomalrods,perhapsreflectingalinkedprocess.MostK+loss,asmeasuredeitherby42K+effluxorK+-ion-selectiveelectrodes,occursaftertheacrosomereactioniscomplete.SinceanelevationofseawaterK+(from10to15mM)ortheadditionof0.5mMtetraethylammonium(TEA),aninhibitorofK+channels,inhibitstheacrosomereactionhalf-maximally,K+movementsoralterationsofK+-dependentmembranepotentialsmayregulatethetriggeringbyjelly.Most,butnotall,ofthe45Ca2+influxisinhibitedwithamixtureof10μMFCCP,1mMCN−,and2μg/mloligomycin,suggestingthatthemitochondriastoremostoftheCa2+.TheextracellularNa+concentrationaffectsCa2+fluxes:spermplacedinto5mMNa+seawaterhaveenhanced45Ca2+uptake,butdonotundergotheacrosomereaction,unless30mMNa+isalsoadded.LowNa+concentrationsleadtospontaneoustriggering,byallowingforbothCa2+influxandNa+-dependentH+efflux.AtleastoneearlyCa2+requirementprecedestheNa+andH+movements,asinferredfromattemptsatreversingtheinhibitorsofjellyinductionoftheacrosomereaction.WhenspermareincubatedwithjellyintheabsenceofCa2+,thenwashedandincubatedwithjellyinthepresenceofCa2+,theacrosomereactionistriggeredonlyuponthesecondincubation.However,whenspermaremixedwithjellyinthepresenceoftheotherinhibitors(verapamil,TEA,5mMNa+seawater,lowpH,orelevatedK+),theyarealteredsothatevenuponsubsequentwashing,jelly-mediatedtriggeringisnolongerpossible.Thissuggeststheexistenceofanintermediatestateinthereactionpathway,thatfollowsaneventforwhichCa2+isrequired,butthatprecedestheNa+andH+movements,whichareinhibitedbyallinhibitorsoftheacrosomereaction.Thesedataareusedtodevelopapartialsequenceofionicchangesassociatedwiththetriggeringmechanism.

[学科分类] 生物科学（综合）

[关键词] TEA;tetraethylammonium chloride;ASW;artificial seawater;MES;2-(N-morpholino)ethane sulfonic acid;DNP;2;4-dinitrophenol;FCCP;carbonyl cyanide p-trifluoromethoxyphenylhydrazone;EGTA;ethylene glycol bis(B-aminoethyl ether)N;N′-tetraacetic acid;CaFSW;Ca2+-free seawater