Spontaneous action potentials and resting potential shifts in fertilized eggs of the tunicate Clavelina☆

摘要

ElectricalactivityinthefertilizedeggofthetunicateClavelinawasstudiedwithmicroelectroderecordingandvoltageclamptechniques.Therestingpotentialcouldassumeeitheroftwostablevalues(approximatelya?’70ora?’30mV)andcouldbeshiftedbetweenthesevaluesbydirectcurrentstimulation.Spontaneousshiftsbetweentwostablerestingpotentialswerealsoseen.Eggcellsproducedactionpotentialsspontaneouslyandinresponsetodepolarizingstimuli.InwardcurrentswerecarriedbybothNaandCaionsandaprominentoutwardpotassiumcurrentwasseenwithdepolarizationtovoltagesabovea?’15mV.Thesteady-statecurrent-voltagerelationship(Ia€“Vcurve)ofthemembraneshowedtwovoltageswherethenetmembranecurrentequaledzero:approximatelya?’35anda?’70mV.Betweenthesetwovoltages,membranecurrentwasinwardandcarriedbynoninactivatingNaandCacurrents.Inwardrectification,whichwasblockedbyexternalRb,occurredatvoltagesbelowa?’70mV.Thevoltagedependenceofinwardrectificationisthoughtbytheauthorstobeimportantforestablishingthemorenegativerestingpotential;itisalsothoughtthepresenceofinwardcurrentwhichdoesnotinactivatecompletelyatvoltagesmorenegativethanabouta?’20mVisanimportantdeterminantofthemoredepolarizedrestingpotential.