Calcium-dependent events at fertilization of the frog egg: Injection of a calcium buffer blocks ion channel opening, exocytosis, and formation of pronuclei☆

摘要

EggsofXenopuslaeviswereinjectedwithacalciumbufferbeforeinsemination,toexaminetheeffectofpreventingorsuppressingthesperm-inducedincreaseinintracellularcalciumonthefertilizationpotential,exocytosis,andpronuclearformation.MicroinjectionofBAPTA[(1,2-bis(o-aminophenoxy)ethane-N,N,Na€2,Na€2-tetraaceticacid)]atconcentrationsbetween0.2and0.7mMusuallysuppressedthefertilizationpotentialtoaseriesoftransientdepolarizations.ThefertilizationpotentialwascompletelyinhibitedwhenthefinalconcentrationofBAPTAintheeggwasgreaterthan0.7mM.Theseobservationssupportthehypothesisthatactivationofthechlorideconductanceresponsibleforthefertilizationpotentialdependsonanincreaseinintracellularcalcium.ExocytosisofcorticalgranulesandelevationofthefertilizationenvelopewerepreventedbyinjectingBAPTAatconcentrationsgreaterthan0.2mM.InjectionofBAPTAtosuppresstheriseincalciumdidnotinhibitspermentryandBAPTA-injectedeggswerehighlypolyspermic.Examinationbylightandelectronmicroscopyrevealedthatspermdecondensationandpronuclearformationwerepreventedbyinjectionofthecalciumbufferbeforeinsemination.