Levis93

Levis93 - Biophysical Journal Volume 65 October 1993...

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Unformatted text preview: Biophysical Journal Volume 65 October 1993 1666-1677 The Use of Quartz Patch Pipettes forLow Noise Single Channel Recording RichardA. Levisand James L.Rae* Department ofPhysiology, Rush Medical College, Chicago, Illinois60612; and *Departments ofPhysiologyand Biophysicsand Ophthalmology, Mayo Foundation, Rochester, Minnesota 55905 USA ABSTRACT Quartz has a dissipation factorof-10 4, which isan order ofmagnitude less than that ofthe best glasses previouslyusedtofabricatepatchpipettes;it'sdielectricconstantof3.8isalsolowerthanthatofotherglasses.On thebasis oftheseelectricalcharacteristicsitisexpectedthatpatchpipettespulledfromquartztubingwillproducesignificantlylessnoise thanpipettesmadefromotherglasses.Ourworkconfirmstheseexpectationsandwe describetheoreticalandpracticalaspects oftheuse ofquartzpipettesforsinglechannel patchvoltageclamp measurements. Methodsforpullingquartzpipetteswith a laser-basedpullerandcoatingthemwithlow-losselastomersare discussed,asareprecautionsthatarenecessarytoachieve lownoiserecordings.We haveshownthatquartzpipettescan bepulledfromtubingwithouterdiametertoinnerdiameterratios as largeas 3and a method ofapplyingheavyelastomercoatingsalltheway tothetipofpipettesispresented.Noisesources arisingfromthepipetteand itsholderare describedtheoretically,and itisshown thatmeasured noiseisingood agreement withsuchpredictions.Withlownoisecapacitivefeedbackelectronics,smallgeometryholders,andthick-walledquartzpipettes coatedwithlow-losselastomerswe havebeen routinelyabletoachievenoiseof100fArms or lessina 5-kHzbandwidthwith realcellpatchesand a pipetteimmersion depth of-2 mm. On occasionwe haveachieved noiseas lowas 60 fArms inthis bandwidth. INTRODUCTION Thebackgroundnoiseinasinglechannelpatchclampmea- surementdeterminesthemaximum bandwidththatwillpre- serveanadequatesignal-to-noiseratio.Atafixed bandwidth, background noise determines the minimum conductance channel which can be studied. Obviously, highresolution measurements requirethatinterferencefromexternalnoise sourcessuchaslinefrequency pick-upbereduced toamini- mum.Asidefromsuchexternalinterference,noiseinpatch clampmeasurementsarisesfroma varietyofsources.These includetheheadstage amplifier,thepipetteand itsholder, and,ofcourse,themembrane-to-glassseal.Inthepast,the patchelectrodehasbeenamajor,ifnotdominant,sourceof noise.Herewe showthatbytheuseofthick-walledquartz pipettescoatedwith low-loss elastomers, thenoiseofthe pipette canbereducedtothepointwhereitissmallerthan thatofeventheverybestpresent-dayelectronics.By using capacitivefeedbackelectronics,small geometryholdersfab- ricated from low-loss dielectrics, and coated quartz elec- trodes,we havebeenabletoroutinelymake singlechannel measurementswithbackgroundnoiselevelslessthan100fA rmsina5-kHzbandwidth.On occasion,noiselevelsaslow as60fArms havebeenachievedinthisbandwidth,which isonlyabout30% greaterthanthenoiseoftheelectronics themselves....
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Levis93 - Biophysical Journal Volume 65 October 1993...

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