Freeze-fracture studies of gap junctions in the developing and adult amphibian cardiac muscle☆

[摘要] Thefreeze-fracturetechniquehasbeenusedtocharacterizethejunctionaldevicesinvolvedintheelectricalcouplingofAmbystomacardiactissue.Thesecellsareconnectedbyjunctionsformedbyeitherlinearorcirculararraysofparticles.Suchstructurescanbeinterpretedasaspecialtypeofgapjunction.Gapjunctionshavealsobeeninvestigatedduringthegrowthanddifferentiationoftwoamphibians,RanaandXenopus.Inbothgeneratheearlieststageofjunctionalassemblyischaracterizedbylinearrowsofparticles.Later,agradualtransformationoftheselinearrowsintocircleswasfound.Finally,inthefullyformedgapjunctions,thesecirclesappearedtojointogetherintoclusters.Insummary,intheadultamphibianmyocardialcells,threedifferenttypesofgapjunctionscanbedescribed.Thefirsttype,whichhasbeenobservedinallembryonicstagesandinadultsinallthreegenera,consistsoflinearorcirculararraysofparticles:thisistheonlytypeofgapjunctionseenatanyageinXenopus.Thesecondtype,consistingofavariablenumberofanastomosingcirclesformingregularnetworks,isneverobservedinembryoniccells.ItistypicaloftheadultfrogheartandmayalsobeseeninAmbystoma.ThethirdtypeischaracteristiconlyofadultAmbystomaheartandconsistsofgeometricallypackedparticlesidentifiablewithclassiccommunicatingmacula.ThefactthatonlythefirstclassofstructureisobservedinXenopusheartstronglysupportstheconclusionthatsuchlineararraysofintramembranousparticlesreallyrepresenttruefunctionalelectricaljunctions.

[学科分类] 生物科学（综合）