The ascidian sperm reaction: Evidence for Cl− and HCO−3 involvement in acid release☆☆☆

[摘要] Ascidiacallosaspermaretriggeredtoundergoinitiationofthespermreaction(mitochondrialswelling)byincreasingthepHorloweringtheNa+concentrationofthemedium.Theoptimal[Na+]foracidreleaseis20mMwithexcellentcorrelationbetweenacidreleaseandinitiationofmorphologicalchanges.Increasingthe[K+]toaround20mMinhibitsacidreleasewhenappliedupto1minaftertriggeringthespermbutwithlessinhibitionat2and4min,suggestingthatK+inhibitsinitiationofacidreleaseratherthanacidreleaseitself.AcidreleaseandthespermreactioncanalsobetriggeredbyCl−-free(NO−3orglutamatesubstituted)seawater(SW).Cl−effluxaccompaniesH+effluxwithtwiceasmanyCl−beingreleasedasH+.BothH+andCl−releaseinCl−-freeSWaredependentuponCO2beingpresentinHCO−3-freemedium,suggestingthatH+effluxisinpartCl−andHCO−3-mediated.However,thechloridechannelblockingagentSITShasnoeffectonH+releaseandaugmentsCl−release.AcidreleaseresultsinasubstantialincreaseininternalpHasdeterminedbypartitioningof9-aminoacridine.Weenvisionacidreleasefromascidianspermasinvolvingtwosystems,theNa+-dependentacidificationsystemofunreactedspermandtheCl−-andHCO−3-mediatedH+releaseatactivation.Themechanismcontrollingacidreleasewouldtheninvolveinactivationoftheinternalacidificationprocessandactivationofthechloride-bicarbonate-mediatedalkalinizationprocess.

[学科分类] 生物科学（综合）