Received1998210207Revised19982122213ThisworkwassupportedbyOverseasStudentsSupportingSchemeofChineseAcademyofSciences(1996),SpecialSupportingSchemeforBiologicalScienceandTechnologyofChineseAcademyofSciences(STZ22217),andNationalFoundationofNaturalScienceofChina(No139740003).ActaPhysiologicaSinica377Aug.1999,51(4),377～385INTERACTIONOFCONESIGNALSONL2TYPEHORIZONTALCELLINCARPRETINA:EXPERIMENTSANDMODELING3LIANGPEI2JI(KeyLaboratoryofNeurobiology,ShanghaiInstituteofPhysiology,ChineseAcademyofSciences,320Yue2YangRoad,Shanghai200031)ABSTRACTIntracellularrecordingsweremadefromtheluminositytypeconedrivenhorizontalcells(LHCs)intheisolatedcarpretinaandmodelanalysiswasperformedtoinvestigatepossiblemechanismsun2derlyingtheinteractionofdifferentconesignalsconvergingontothesecells.ItwasobservedthatagreenbackgroundlightenhancedtheLHC′sredresponse,andsuchenhancementwascloselyrelatedtotheactiva2tionofgreencones.Modelanalysisshowedthattheactivityofbothglutamate2andGABA2relatedpathwayswerepotentiatedduringgreenbackgroundillumination.GABAapplicationdidnotabolishtheresponseen2hancement.ItisspeculatedthattheextentoftheLHC′sresponseenhancementmaybedeterminedbythebalanceoftheincreasedactivitybetweenthefeedforwardandfeedbackpathways.Keywords:isolatedcarpretina;horizontalcell;interaction;modelanalysisInlowervertebrateretina,luminositytypecone2drivenhorizontalcells(LHCs)arehyperpolar2izedbylightstimulus.Itiswellacceptedthatthehyperpolarizationresultsmainlyfromalight2in2duceddecreaseoftheexcitatoryneurotransmitter(glutamate)releasedbyphotoreceptors[1～4].Therapiddecreaseinconcentrationofglutamateinthesynapticcleftmediatesabriefchangeincationchannel′sconductance,andthusresultsinaswiftdynamicsofLHC′smembranehyperpolarization.This,inturn,causesadecreaseinconcentrationoftheinhibitoryneurotransmitterγ2aminobutyricacid(GABA)releasedbyhorizontalcells,whichcontributestoregulatetheLHC′sresponsedynam2icsbychangingtheactivityofanionchannelonthemembrane[5,6].Itwaspreviouslyreportedthatinteleostfish,redresponsesofLHCwereenhancedbygreenbackgroundillumination,whichwasthoughttobecausedbyaninteractionofdifferentconesignalsconvergingontoLHC[7～12].SinceitwasobservedthataprecedinggreenconditioninglightenhancedtheLHC′sresponsetoasubsequentredstimulus[7,8],itwasthusassumedthattheinputfromgreen2sensitiveconesactsontheinputfromred2sensitivecones,whichresultsintheenhancementinLHC′sredresponses.Accordingtothemodelsdescribingsynapticconnectionbetweenhorizontalcellsandcones,theresponseenhancementisthoughttobeattributedtoachangeintheactivityoftheGABA©1995-2005TsinghuaTongfangOpticalDiscCo.,Ltd.Allrightsreserved.mediatedfeedbackpathway[8,10].However,littlehasbeendonetoexaminethevalidityofthepro2posedmodels.Thecurrentstudyaimedtoinvestigatepossiblemechanismsunderlyingthesignalinteraction2in2ducedresponseenhancement.Thefollowingaspectswereinvestigated:(1)therelationshipbetweentheresponseenhancementandtheactivityofrelevantneurons;and(2)therelationshipbetweentheenhancementandtheactivityofrelevantneurotransmitters.Experimentswereconductedundervariousconditions.Aquantitativemodelwasemployedfortheanalysis,andparametersestimatedfortheglu2tamateandGABArelatedcomponentswerecomparedunderdifferentchromaticadaptationconditions.1MATERIALSANDMETHODS111Experimentalaspects11111PreparationExperimentswereperformedonisolatedcarp(Carassiusa...
