Distribution and density of α-bungarotoxin binding sites on innervated and noninnervated Xenopus muscle cells in culture☆

[摘要] Thedistributionanddensityofα-bungarotoxin(α-BT)bindingsitesonXenopusmusclecellsinculturebyautoradiographyusing125I-α-BTwereexamined.Inmusclecellsgrownaloneα-BTbindingsiteswerefairlyuniformlydistributedovertheentiresurfacewithameandensityof104/μm2(backgrounddensity).Occasionally,spotsofhigherdensitywereobserved(“hotspots”)wherethemeandensitywas890/μm2.Theadditionofneuraltubecellsdidnotchangethebackgrounddensity.Similarlyinthemajorityofcasesmediumcontainedwithneuraltubecellsdidnotaffectthedensityofα-BTbindingsites.Previousfindingsthatthebackgroundacetylcholinesensitivityofmusclecellsincreasedinthepresenceofneuraltubecells(byapproximately50%)orinconditionedmedium(byapproximately70%),therefore,arenotlikelydueprimarilytoanincreaseintheacetylcholinereceptor(AChR)density.Incoculturesofnerveandmusclecellsregionsofhighα-BTbindingsiteswereoccasionallyassociatedwiththepathofneurites.Insuchregionsthedensityofα-BTbindingsiteswasestimatedtobeapproximately1000/μm2.However,eveninthesecellsthedensityatnon-nervecontactedregionswasnotdifferentfromthatinmusclecellsculturedalone.WhethertheincreaseinAChRdensityatthejunctionalareaissufficienttoexplainapreviousobservationofafivefoldincreaseintheamplitudeofspontaneoussynapticpotentialsduringtheprocessofAChRaccumulationisdiscussed.

[学科分类] 生物科学（综合）