Copyright 1973. All rights reserved INTERPRETATION OF SOME MICROELECTRODE MEASUREMENTS OF ELECTRICAL PROPERTIES OF CELLS A. PESKOFF AND R. S. EISENBERG UCLA School of Medicine, Los Angeles, Califoria 9022 Inrecentyearsmostmeasurementsothenaturalelectricalactivityof cellssuch asaction potetials and synaptic potentials have been carried out using a micro electrodetorecordtheelectricalpotentialdiferencebetweenthecellinterioranda reference electode in the surrounding saline solution. This is a sensible way to measurenatural electrcalactivitysince thepotentialrecordedisadecentapproxi maton to thepotential across thecellmembrane and this membranepotentialis usuallythenatralelectricalactivityofinterest inthecelltswelltorememberthat some naturalelectrical activity, such as thatwhichmay occur within intracellular organelleslikemitochondriaorsarcoplasmicreticulum,mightnotbesimplyrelated tothepotentialacrossthecellmembrane. Themechanismofthisnaturalelectricalactivitydependsontheelectricalparam etersofthecellwhicharemeasuredbyapplyingcurrenttothecellandrecording andanalyingtheresultingpotentialchangeĮInordertoperformthisanalysis,itis necessarytoknowthespatialdistributionofcurrent fow,thatistosay,themagnitude anddirectionofcurrentfow,especiallytheamountofcurrentthatcrossesthemem brane.Whileitispossibleinsomespecialcases(eg.odgkin & ushton 1) toapply currentoutsideacellandanalyzeinareasonably unique mannerwhereandhow currentisowingacrossthecellmembrane,itisnoteasytodothisingeneral.The problemisessentiallythatthemembraneisastructureofveryhighimpedancean somostofthecurrentowsaroundthecellnotthrought.Theamountofcurrentthat crossesthemembraneisonlyasmallperturbationonthelargequantityofcurrent fowingintheextracellularsolution.Whencurrentisappliedinsideacellhowever allofitmustfowacrossthecellmembranetothereferenceelectrodeoutsideandso theproblemofanalyzingthepatternofcurrent fowacrossthemembraneisgreatly simplied.Forthisreason,mostmeasurementsof theelectricalpropertiesofcells use a microelectrode source of current the current-passingmicroelectrode being insertedintothecell.Thepotentialproducedbythiscurrentfowisoftenrecorded by another microelectrode inserted into the same cell, although at times a single microelectrodeisusedbothtorecordpotentialandpasscurrent. The original theoretical analysis of the electrical properties of cells was carried outforotherexperimentalarrangements(Cole &odgkin2, odgkin&Rushton ), 65 Annu. Rev. Biophys. Bioeng. 1973.2:65-79. Downloaded from www.annualreviews.org by UNIVERSITY OF ILLINOIS - CHICAGO on 09/16/10. For personal use only.