The ionic components of the current pulses generated by developing fucoid eggs☆☆☆

[摘要] Usinganewlydeveloped,extracellularvibratingelectrode,westudiedtheioniccompositionofthecurrentpulseswhichtraversethedevelopingPelvetiaembryo.ExternalNa+,Mg2+,orSO42−,arenotneededforthefirst20minofpulsing.Infact,loweringexternalNa+orMg2+(orK+)actuallystimulatespulsing.SincetracerstudiesshowthatCa2+entryisspeededbyNa+,Mg2+,orK+reduction,thesefindingssuggestthatCa2+entrytriggerspulsing.AsevenfoldreductioninexternalCl−raisespulseamplitudesby60%.Moreover,Cl−istheonlymajorionwithanequilibriumpotentialnearthepulsereversalpotential.ThesefactssuggestthatCl−effluxcarriesmuchofthe“inward”current.WeproposeamodelforpulsinginwhichincreasedCa2+withinthegrowingtipopensCl−channels.TheresultingCl−effluxslightlydepolarizesthemembraneandthusdrivesabalancingamountofK+out.Thus,thepulsesreleaseKClandservetorelieveexcessturgorpressure.BylettingCa2+intothegrowingtip,theyshouldalsostrengthenthetranscytoplasmicelectricalfieldwhichispostulatedtopullgrowthcomponentstowardthistip.

[学科分类] 生物科学（综合）