Sciatin: A myotrophic protein increases the number of acetylcholine receptors and receptor clusters in cultured skeletal muscle☆

[摘要] Factorspresentinneuralextractsorinmediaconditionedbyneuronshavebeenshownbyotherstoincreaseboththenumberofacetylcholinereceptors(AChRs)andthenumberofreceptorclustersinculturesofembryonicskeletalmuscle.Wehaverecentlyshownthattheglycoprotein,sciatin,exertstrophiceffectsondevelopingmuscleinvitro.Inthepresentstudy,weinvestigatedtheeffectofsciatinonAChRsinaneuralculturesofchickskeletalmuscle.SciatincausedasignificantincreaseinthenumberofAChRs/dishasmeasuredbybindingof125I-α-bungarotoxin(α-Btx)andinacetylcholinesterase(AChE)activity/dishindifferentiatingmusclecells.TheincreaseinAChRselicitedbysciatinwasduesolelytoincreasedreceptorsynthesisandincorporation.TherateofAChRsynthesisinsciatin-treatedcultureswasasmuchasfivetimesthecontrolrateandwassignificantlyreducedbycycloheximide(10μM).AChRdegradationwasunaffectedbythemyotrophicprotein.AlthoughthenumberofAChRs/dishwasincreasedbysciatinduringmyogenesis,AChRspecificactivity,expressedaspicomoles125I-α-Btxbound/mgcellprotein,wasonlytransientlyincreasedbythemyotrophicprotein.ThiscontrastedwithAChEspecificactivityinsciatin-treatedcultureswhichremainedelevatedthroughoutdifferentiation.Autoradiographsof125I-α-Btx-labeledculturesshowedthatsciatincausedanincreaseinthenumberandsizeofAChR“hotspots”andmaintainedtheintegrityoftheseAChRclustersinaneuralmuscleculturesforupto5weeks.Atthistimecontrolcultureshadcompletelydegenerated.ThemechanismbywhichsciatinenhancedthesynthesisofAChRsappearedtobedistinctfromthatoftetrodotoxin(TTX),anagentwhichabolishesmuscleactivity.However,liketheophylline,sciatinmightevokeincreasedsynthesisofAChRsviaregulationofcyclicAMPsincethemyotrophicproteinincreasedcAMPbothincellsandinconditionedmedium.Theresultsofthisstudysuggestthatsciatinmayberelatedtothediffusiblefactor(s)frommotorneuronsdescribedbyotherswhichhastrophiceffectsonAChRs.Furthermore,wesuggestthatthismyotrophicproteinmayberesponsiblefortheclusteringofAChRsandmaintenanceofreceptorclustersatneuromuscularjunctionsindevelopingavianmuscle.

[学科分类] 生物科学（综合）