The fertilization potential and associated membrane potential oscillations during the resumption of meiosis in the egg of the ascidian Phallusia mammillata

摘要

ThefertilizationpotentialinPhallusiamammillataconsistedofaninitialrapiddepolarization.Thisinitialspermtriggereddepolarizationwasfollowedbyaphaseofmembranedepolarizationwhichwasofeitherlongorshortduration,dependingontheeggs.Whenoflongduration,thephaseofmembranedepolarizationwasdividedintotwoperiods:thefirstonebeganwithaplateau(Em=+20.2?±1.1mV;duration=1.7?±0.14min)whichwasfollowedbyaseriesofmembranepotentialoscillations(n=3.1?±0.25)lasting2.4?±0.2min.Thesecondperiodalsobeganasaplateau(Em=a??0mV;duration=3.40?±0.20min)whichwasfollowedbyaseriesofoscillations(n=11.5?±0.5)lasting11.8?±0.6min,followedbyamembranerepolarization.Thesecondseriesofoscillationsoftencontinuedrisingfromtherestingpotentialvalue.Intheeggsdisplayingashortdurationofmembranedepolarization,thesecondperiodofdepolarizationwasshortened(lastingonly3.5?±0.5min)sinceitlackedthesecondplateau.Inadditionitdisplayedasmallernumberofoscillations(n=4.7?±0.6).Asaconsequenceofthisshortening,themembranerepolarizedsooner.Afterrepolarization,themembranedisplayedseveralpotentialoscillationsthatstartedfromtherepolarizationlevel.Regardlessofthelengthofthedepolarizedplateauphases,thetotalnumberofmembraneoscillationsandthetimeperiodduringwhichtheyoccurredwereconstant.Eggsdisplayingalongdepolarizationphasehad15.9?±0.6oscillationsina19.5?±0.6mininterval,whileeggshavingashortdepolarizationphasehad16.0?±0.8oscillationsina18.1?±0.3mininterval.Thetimeperiodduringwhichthepotentialoscillationsoccurredcorrespondedremarkablywellwiththetimeofthemeioticdivisions:theformationofthefirstpolarbodywasdetectedabout80secaftertheendofthefirstseriesofoscillations;thesecondpolarbodywasextrudedabout85secafterthelastmembraneoscillationoccurred.