細(xì)胞的基本功能3-2008

1、Summary of Membrane ReceptorsFig 2Fig 3安靜時(shí)膜對(duì)K+有permeability； K的電化學(xué)驅(qū)動(dòng)力：K有向細(xì)胞外擴(kuò)散的動(dòng)力膜兩側(cè)的離子濃度梯度膜兩側(cè)的電位差形成的電位梯度；為細(xì)胞膜保持膜內(nèi)較膜外為負(fù)的基礎(chǔ)K+外流Na+內(nèi)流膜內(nèi)外離子濃度梯度的維持：Na+ K+ pump影響靜息電位的主要因素：膜內(nèi)、外K+濃度差；膜對(duì)K+和Na的相對(duì)通透性；NaK泵活動(dòng)的水平。Fig 膜通透性：膜通透性：膜允許某種物質(zhì)從膜的一側(cè)轉(zhuǎn)移到另一側(cè)的能力膜電導(dǎo)膜電導(dǎo) (G)：膜運(yùn)送帶電離子，形成離子電流的能力電壓鉗（電壓鉗（voltage clamp）：又叫電壓固定）：又叫電壓固

2、定原理：原理：歐姆定律 V=IR；膜電導(dǎo) (G) = 1/膜電阻 (R) 跨膜離子電流 (I) = V/R = VG; 只要固定膜電位 (V), 測(cè)出的跨膜電流 (I) 的變化，既可反應(yīng)膜通透性的改變工具藥：工具藥： Na+通道阻斷劑河豚毒 (tetrodotoxin, TTX) K+通道阻斷劑 四乙基胺 (tetraethylammonium, TEA)膜片鉗膜片鉗 (patch clamp) 是一種記錄膜結(jié)構(gòu)中單一通道的開(kāi)放和關(guān)閉，測(cè)量單通道離子電流I和電導(dǎo)G的技術(shù) Fig電壓鉗（voltage clamp）和膜片鉗 (patch clamp)的應(yīng)用 FigAction potential

3、 (AP) 和門控通道和門控通道 膜對(duì)膜對(duì)Na、K通透性發(fā)生變化而形成。通透性發(fā)生變化而形成。AP 原理：原理：depolarizationNa+內(nèi)流 (Na+ ion channel) repolarizationK+外流 (K+ ion channel)AP和細(xì)胞興奮性的變化和細(xì)胞興奮性的變化絕對(duì)不應(yīng)期：絕對(duì)不應(yīng)期：興奮性興奮性0，Na通道失活狀態(tài)通道失活狀態(tài)相對(duì)不應(yīng)期：相對(duì)不應(yīng)期：閾上刺激才引起興奮，閾上刺激才引起興奮，Na通道尚未恢復(fù)正常通道尚未恢復(fù)正常超常期：超常期：閾下刺激既可引起興奮，閾下刺激既可引起興奮，Na通道恢復(fù)正常通道恢復(fù)正常低常期：低常期：閾上刺激才引起興奮，閾上刺激才

4、引起興奮，Na通道恢復(fù)正常，但通道恢復(fù)正常，但Na泵活動(dòng)增強(qiáng)，泵活動(dòng)增強(qiáng)，超極化狀態(tài)超極化狀態(tài)FigFigSummary:膜的 depolarization Na+ channel打開(kāi)Na+內(nèi)流 Na+ equilibrium potentialFigNa+ channel關(guān)閉K+ channel延遲開(kāi)放repolarizationAfter hyperpolarization voltage gated channel 在膜電位返回resting potential 之后才開(kāi)始關(guān)閉FigFigCytosolExtracellularfluidCation +Anion -VoltmeterA

5、nion -Anion -Anion -Cation +60- 0 + 0 -Er = 70 - 75 mV- 0 +DiffusionInsideOutside(a) Developing membrane potentialmVCell90DiffusionChargeInsideOutsideCell(b) Electrochemical equilibriummVPotassium ionOrganic anion- 0 +-StimulatorAxonMicroelectrodeInside axonCROOvershootStimulus appliedTime (msec)Aft

6、er-hyperpolarizationgKgNaRepolarizationDepolarizationVm(mV)OvershootCLOSEDOPEN(a) Ion channel(b) Voltage-gated channel(c) Ligand-gated channelResting state-90 mVVoltage-gated sodium ion channelActivation state-60+30mVInactivation state+30-90mVVoltage-gated potassium channelOpen+30-90mVClosed-90+30mV

7、Na+ channelsK+ channels1. Resting state2. Depolarization3. Depolarization4. RepolarizationThresholdRestingRestingRestingRestingRestingThresholdThresholdThresholdThreshold5. HyperpolarizationStimulus appliedTime (msec)gKgNaVm(mV)少量少量Na 通道開(kāi)放通道開(kāi)放大量大量Na 通道開(kāi)放通道開(kāi)放Na 通道關(guān)閉，通道關(guān)閉，K通道完全開(kāi)放通道完全開(kāi)放K通道延遲開(kāi)放通道延遲開(kāi)放Na

8、K泵運(yùn)轉(zhuǎn)泵運(yùn)轉(zhuǎn)After-hyperpolarizationRepolarizationDepolarizationK通道持續(xù)開(kāi)通道持續(xù)開(kāi)放放Stimulus#1Stimulus#2 (stronger)Time (milliseconds)Note the changes in threshold potential and AP amplitudeNon-refractoryperiodRelative Refractory Period (RRP)Absolute Refractory Period (ARP)Action Potential (AP)ThresholdThreshold

9、Membrane Potential (mV)AxonhillockShort Time ConstantTimeLong Time ConstantThresholdTimeMembrane potential at axon hillock (mV)Membrane potential at axon hillock (mV)AxonhillockTime Single excitatory postsynaptic potentialThresholdMembrane potential at axon hillock (mV)AxonhillockTime Single excitat

10、ory postsynaptic potentialThresholdMembrane potential at axon hillock (mV)AxonhillockTime Simultaneous excitatory postsynaptic potentialThresholdMembrane potential at axon hillock (mV)ABCDESinkSourcePropagationPropagationNodes of Ranviert1t2t3t4Sink SourceSink SourceSink SourceSink SourceSink SourceSink Source Sink SourceSink SourceUNMYELINATED AXONAction potential generated at each succeeding adjacent membrane segmentMYELINATED AX