class-10-第四章-神经生物物理学-1.ppt

Patch clamp configurations (膜片钳的种类) Inside-out: the intracellular surface of the patch membrane faces the bath solution. Outside-out: the extracellular patch surface faces the bath solution. Whole cell patch clamp: patch pipette is attached to a whole cell Whole-cell Patch (Voltage) Clamp 动作电位产生的离子机制： Changes in Membrane Conductance to Na+ and K+ Underlying Action Potential Membrane potential (Vm) Conductance (G) Vm (Action potential) Time -60 +30 0 -30 ION OUT (mM) IN (mM) OUT/IN Enernst (mV) Na+ 145 12 12 +67 K+ 4.5 155 0.026 -95 Changes in Membrane Conductance to Na+ and K+ Underlying Action Potential Membrane potential (Vm) Conductance (G) GNa GK Vm (Action potential) EK= –95 mV ENa=+67 mV Time -60 +30 0 -30 Changes in Membrane Conductance to Na+ and K+ Underlying Action Potential During an action potential Depolarization cause membrane potential reaches the threshold Voltage-gated Na+ channels activated, (Na+ conductance GNa+ increased), Na+ ions flux into the cell (inward current). Membrane potential shifts towards the Nernst Potential of Na+ and gets depolarized further. K+ channels activated, (conductance GK+ increased). K+ ions flux out of the cell (outward current). Na+ channels become inactivated Membrane potential repolarized K+ channels inactivated. (二)阈电位(局部电位)与动作电位的关系 ◆水平——比Rp绝对值小10～20mV (-70～-50mV)。 阈电位 产生Ap的必要条件 ◆意义—— 兴奋性＝1／RP与阈电位之差值 Dissection of Na+ and K+ currents by specific channel inhibitors TTX, Na+ channel inhibitor TEA, K+ channel inhibitor STX, Na+ channel inhibitor Total membrane ionic current A stepwise depolarization stimulus imposed on axon…… Thus the total membrane ionic current is the summation of Na+ and K+ current…… Q: What if a hyperpolarization was imposed on axon? This is “delayed rectifier” K+ current! During an action potential, Na+ current is initiated at negative voltage (~-30 mV) when membrane is depolarized. Because [Na+]o[Na+]i, opening of Na+ channels cause inward current, which causes further depol