Ion Channels are Gated Pores - mcb5068.wustl.edu...revealed by currents through single ion channels....
Transcript of Ion Channels are Gated Pores - mcb5068.wustl.edu...revealed by currents through single ion channels....
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IonChannelsareGatedPores
JimHuettner
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LectureOverview
• Review of cellular electricity • Recording cellular electricity • Theories about channel selectivity • Channel structures and selectivity • Voltage-dependent gating • Channel-lipid interactions • Ligand-gated channels • Aquaporins and connexins
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IonConcentrations
Na 117 K 3 Cl 120 Anions 0 Total 240
Na 30 K 90 Cl 4 Anions 116 Total 240
[+ charge] = [- charge] 0 mV
[+ charge] = [- charge] -89 mV
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Channelsarecatalysts–Enzymesforthetranslocationofions
Channelshavetwofundamentalfeatures:
(1)Poreproperties(2)Gating
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RecordingMembranePotential
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howtomeasurecurrentA voltage clamp can control the voltage across the membrane and record the current that passes through the membrane. Ohm’s Law says: Voltage = Current * Resistance Circuitry in the voltage clamp controls Voltage
When channels open, Resistance will change and the
device will measure Current. Resistance = 1 / Conductance so another form of Ohm’s Law is: Current = Conductance * Voltage
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patch-clampversus2-electrodeclamp
patchclamp twomicroelectrodevoltageclamp
Vm = Vc
Im
Vc
Vm
Vc Im
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formingatightseal
Sakmann,B(1992)Neuron8:613-629
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whole-cellandoutside-outpatch
10 µm Sakmann,B(1992)Neuron8:613-629
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Howdoesachannelachieveselectivity?
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Howdoesachannelachieveselectivity?
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ChannelNomenclature
• Namedbyfunction:delayedrectifier,inwardrectifier,L-typecalciumchannel,NMDAreceptorchannel,etc.
• Namedbystructure:Kv1.1,Kir6.2,Cav1.1,NR1,etc.
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ChannelSubunitTopology
KcsA, a bacterial K channel, the first channel crystalized
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ChannelDendrogram
https://www.guidetopharmacology.org/GRAC/ReceptorFamiliesForward?type=IC
Rationalefordiversity?• Permeability• Kinetics• Modulation• TraffickingSignalIntegration
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StructureofaPotassiumChannel
Doyleetal.,(1998)Science280:69-77
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SelectivityFilterandSpace-FillingModel
Doyleetal.,(1998)Science280:69-77
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ioncoordinationinthe“selectivityfilter”
GouauxandMacKinnon(2005)Science310:1461-1465
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viewsofthechannelopenandshut
Jiang et al., (2002) Nature 417:515-522
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voltage-gatedchannels
Long et al., (2005) Science 305:897-903
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viewfromtheextracellularspace
Long et al., (2005) Science 305:897-903
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voltage-dependentgating
Jiang et al., (2003) Nature 423:33-48
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Longetal.,(2007)Nature450:376-382
lipidsco-crystallizedwiththechannel
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Lipidco-crystallizedwithKcsA
Valiyaveetiletal.,(2002)Biochemistry41:10771
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PIP2isrequiredforeukaryoticKchannelactivitybutinhibitsabacterialKchannel
D’Avanzoetal.,(2010)JBC285:37129
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Suh & Hille (2008) Ann. Rev. Biophys. 37:175-195
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Kir2.2withoutandwithPIP2
Hansenetal.,(2011)Nature477:495
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familiesofligand-gatedchannels
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AChRHydropathyPlot
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AChRsubunittopology
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M2HelixDeterminesConductance
Sakmann,B(1992)Neuron8:613-629
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imagesofthenicotinicAChR
ToyoshimaandUnwin,(1988)Nature336:247-250
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α4β2nicotinicreceptor
Morales-Perezetal.(2016)Nature538:411-415
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Sobolevskyetal.,(2009)Nature462:745-756
GluA2glutamate(AMPA)receptor
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P2X4purinergicreceptor
Kawateetal.,(2009)Nature460:592-598
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Aquaporinwaterchannel
Luckey,2nded.Fig.12.6
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AquaporinSelectivity
Albertsetal.,6thed.
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IntercellularConnexinsChannels
Meyersetal.,(2018)Nature564:372-377
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AdditionalReading• Sakmann,B.(1992)Elementarystepsinsynaptictransmission
revealedbycurrentsthroughsingleionchannels.Neuron8:613-629.
• DoyleDA,MoraisCabralJ,PfuetznerRA,KuoA,GulbisJM,CohenSL,ChaitBT,MacKinnonR.(1998)Thestructureofthepotassiumchannel:molecularbasisofK+conductionandselectivity.Science280:69-77.
• Gouaux,EandMacKinnonR.(2005)Principlesofselectiveiontransportinchannelsandpumps.Science310:1461-1465.