Class Note for BME 510 at UA
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Date Created: 02/06/15
Action Potentials and Conduction Generation of action potentials Voltageclamp and membrane currents underlying action potential Sodium and potassium currents Inactivation Relationship to singlechannel currents Intracellular recording of the action potential in a squid axon from Hodgkin and Katz 1949 7quot Cnpyagmmooz Erma Silent lUSA All righ reserved Voltage clamp of the squid giant axon from Hodgkin Huxley and Katz 1952 Command ponenual cuneni eiecnoas Cuma39il iniecnon vmmga record wings eieclroe o V Cunsnl mommy FIGURE 5 Vnigeanp technique The vnlnguclnmp Itchniqm keeps me vnlmge mm lhc membrane cmlslam 4 ha me amniiiudc and nine cams or Ionic cuncim can be nnensumt In the Morelccllode vollagoclamp technique one cleaned mensnnes me vollag mass m nleii39lirmle while me other Mucus cunenl inm me cell io keep the olmg cmislmu The EKpClillVL nlrr scls n wing in which m Man or imnnn is m b aninsn mic comnmild poisnnnii Cumin in men n ncind nin mu ccH in pmpnmn hi im mm m humanquot Ic nmnni ilwmlinmc polcmml and In conuuand pnmn 111 feedback cyc c 0mm cm nnnnnin mmny damping llu iiicmbmnc new II in it cmunmml polcn nicnsning me amonin ofcun em waned m cxpenrucmercml dclsrmme m alupluudc and um cmlrs of me ionic cumin owing across in membrane iRUM MDLhCULI39Ih T0 NETWORKS John H lbrn mm In Rnim a 10m lammi Inn All I gun mu Feedback Command Signal CurrenteeCtF0de amplifier potential generator W A lmVl c Vrn 5o Axon A 60 7 Current monitor 39 OUtward Current u m 0 electrode Inward T i O Vm B Membrane 0 39 potential amplifier Vm Small depolarizing commands evoke a capacitive current and a small outward leakage current Larger depolarizing commands evoke an m early negative inward current 0 followed by a delayed outward current Voltage clamp of the squid giant axon reveals nonlinear voltage dependent currents Hodgkin Huxley and Katz 1952 The peak early and late currents are typically plotted as a function of voltage following subtraction of the capacitive and leakage currents A1 Vm w sn mV I new i ms Ilme B Current Voltage I V Relationships 1quot mAcma The earlyinward current is eliminated by replacement of external Na with an impermeant cation Subtraction reveals the lateoutward current which can be shown to be carried by K from Hodgkin and Huxley1952 As expected the early and late currents become zero when the axon is clamped at the equilibrium potentials for Na and K respectively At Control A2 Na tree 52 mil 4 mV 4 mv w qu mv Jm fmz nus n2 lNa and 1K Ix 39m39lm lm iconhull Membrane current rnAcm2 Two methods for separating currents use with caution Outward y IK Na a tree seawater Ion replacement 1m seawater Iue Um 39 IKJ B Pharmacologica blockade 1 Control m5 LE 5 m 75mV an 145 ll 30 VS HAO 9 5 TTX K current I 75mv 2 k 4 45 an 85 45 3 TEA Na current Na 15 60 45 an 15 7A5 730 45 CnpytightOZDOZ EkavterSmenze tum A right veielvrd A mS cm2 20 10 20 10 20 10 10 10 Time and Voltage Dependence of Conductance Increases from Hodgkin and Huxley 1952 B o 8K 20 gN Sodium Potassium a conductance conductance 44 mV 15 0 o E E 10 23 mV g E 5 8 U m f O I I I l I 80 60 40 20 0 20 40 60 27 mV W Vm mV so E quot 39 mV M W I I l I I I I I I I I I I I I 0 2 4 0 2 4 6 8 E Action potential TLme ms 0 g Na conductance Na channels m g 39 K conductance K channels g V E g Ion Ion m Ion 2 50 4o 20 auequauI Io um 19 sIeuueLIa uedo A doublepulse or prepulse voltageclamp protocol reveals voltagedependent inactivation of Na current from Hodgkin and Huxley 1952 A Membrane potential Membrane current 21 Resting potential 65 mV mV 3 C 105 85 65 45 25 D 21 Prepulse poten al mV mV 45 65 I I 0 20 40 60 O 20 40 Time ms Time ms Model of the nerve cell axon and currents underlying the action potential from Hodgkin and Huxley 1952 Extracellular side 1 Na i 9N 1m Q Voltage clamp 1K1 9 EK II II E Na Cytoplasmic side We may rst collect the equations which give the total membrane current I 35 a function of time and voltage These are I01i1515 xn4 Ifmammal VanH ilV Vil dnfd mn n 8quotn dmdtaml m 3mm Iii114180 7h na 26 7 15 16 where The HodgkinHuxley model for Na channel gating is largely borne out by information about the molecular structure and singlechannel currents 1 Resting closed 2 Activated open Extracellular suds i Fast channel opening gt Cytoplasmic side Inactivation Activation gate 9816 3 Inactivated closed Patch pipettes can be used to measure single channel or wholecell current The conformation can be varied to allow intracellular andlor extracellular solutions to be controlled The wholecell mode may also be used for voltage recording Pipette Monitor Smauar Assoclams Inc Patch clamp records from single Na channels reveal both voltagedependent and timedependent probability of opening and single channel conductance B Time ms 2001 Sinauar Associates Inc vm npmun zanm 4 Multiple channels in a n WW single patch Note that 2 the probability of WW channel opening is timedependent WFMWWW umsvuewt Texrodomxm which t pzmnes pm W bledlt5 Na channels abolishes the cunent Average WW current pA 1 W 0 10 20 so 40 50 T mEUVISeC 392 One mum am 4 Twu manners wen Tmee ahannaL npun u w 20 an on so metmsec A slNELEOAANNEL l v aunmsmps mm mm M The voltage dependence of the m l T m macroscopic whole cell Na current re ects the voltage micssmssrsc sssmm dependent probability of opening for single 2 channels um currlnl l a when NW C azcwsmumzmvazwmsmw Mlcrwsmniczw39nl my Propagation occurs as current generated during the action potential depolarizes adjacent axonal membrane to bring it to threshold The longitudinal spread of current and hence the speed of action potential propagation is enhanced by myelination A UNMYELINATED Ilon A mmquot mm an hm up in am layers ulmemtn ne
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