Initiation of the activation potential by an increase in intracellular calcium in eggs of the frog, Rana pipiens☆

[摘要] Themembranepotentialofthefrogeggundergoesatransientpositiveshiftatfertilizationwhichisablocktopolyspermy.Thispaperaddressesthequestionofhowaspermelicitsthis“fertilizationpotential.”IontophoreticinjectionofCa2+activatesRanapipienseggstodevelopandinitiatesatransient,positive-goingshiftinthemembranepotential(theactivationpotential)whichislikethesperm-inducedfertilizationpotentialinamplitude,duration,andCl−dependence.ActivationpotentialsareelicitedbyCa2injectionintobothanimalandvegetalregionsoftheegg,buttherateoftheinitialdepolarizationismuchlesswhenCa2+isinjectedintothevegetalregion.InjectionsofK+,Na+,Cl−,orMg2+donotresultinactivationpotentials,buttheCa2+analogs,Sr2+andBa2+,cansubstituteforCa2+.Treatmentofeggswiththedivalentcationionophore,A23187,alsoinitiatesatransient,positive-goingdepolarization.BecauseinjectionofCa2+issufficienttoelicitaresponsealmostidenticaltoafertilizationpotential,theiontransportmechanismsnecessarytoproduceafertilizationpotentialmustpreexistintheunfertilizedeggs;thespermcontributesonlythestimulustoactivatethesemechanisms.TheresultsreportedheresuggestthatthestimulusmaybeariseinfreeCa2+.

[学科分类] 生物科学（综合）