Changes in voltage-dependent currents and membrane area during maturation of starfish oocytes: Species differences and similarities☆

摘要

FullgrownstarfishoocytesarearrestedatmeioticprophaseIintheovary.Thenaturalhormone1-methyladeninetriggersoocytematurationwhichinvolvesmeiosisreinitiationalongwithavarietyofmorphological,biochemical,andelectricalchanges.Instudyingoocytesoftwospecies,HenricialeviusculaandAsterinaminiata,usingthevoltage-clamptechnique,wefoundinterestingdifferencesandsimilaritiesintheelectrophysiologicalchangeswhichoccurredduringmaturation.Oocytesofbothspecieshavethreemajorvoltage-dependentcurrents:aninwardCa2+current,aninwardlyrectifyingK+current,andatransientoutwardK+current(A-current).TheCa2+currentandtheA-currentweresimilarinthetwospeciesbuttheinwardrectifierinHenriciahadactivationkineticsthatweremorethan10-foldslowerthaninAsterina.Nonetheless,allthreecurrentswereaffectedsimilarlyduringmaturation:theinwardCa2+currentsremainedconstantinbothspecies,whilethetwoK+currentsdecreasedinamplitude.InHenriciathemembranesurfaceareadecreasedsubstantiallyduringmaturation,whileinAsterinaitremainedconstant.ThismaybeexplainedbythemorehighlyinfoldedstateofthemembraneintheimmatureHenriciaoocyte.TheselectivelossofK+currentfollowedthetimecourseoftheareadecreaseinHenricia,butthesamepercentagedecreaseincurrentoccurredinAsterinawithoutanetmembraneloss.