The regulation of acrosomal exocytosis: I. Sperm capacitation is required for the induction of acrosome reactions by the bovine Zona pellucida in vitro☆

摘要

Theregulationofacrosomalexocytosisincapacitatedbovinespermatozoabysolubleextractsofzonaepellucidaewasexamined.Kineticstudiesdemonstratedthatzonaepellucidaestimulatedsynchronousacrosomereactions.Thet12ofthisprocesswas5a€“10minandresponsewasmaximalat20min.Theapparentinitialrateofexocytosisinspermpopulationswasdependentupontheconcentrationofzonapellucidaprotein,withanED50andamaximallyeffectivedosageof20and50ngprotein/??l,respectively.Zonaepellucidaecauseduptoa48-foldincreaseintheapparentinitialrateanda3-to4-foldstimulationinthenetoccurrenceofexocytosis.Incontrast,solubilizedzonaepellucidaedidnotinduceacrosomereactionsinuncapacitatedsperm.Thedevelopmentofacapacitatedstate,asassayedbytheabilityofspermtofertilizeeggsinvitro,wascomparedtotheexpressionofzonapellucida-regulatedacrosomereactionsinaseriesofkineticexperiments.Bothactivitiesweremanifestwithsimilarkineticsanddisplayedidenticaldependenciestowardstimulatoryandinhibitoryagentsinvitro.Itisconcludedthatcapacitationisanessentialprerequisitefortheinductionofacrosomalexocytosisinbovinespermbythezonapellucida.