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1、chap. 2 The resting membrane potential,chap. 3 Action potential,第二章 细胞的兴奋,from Berne & Levy Principles of Physiology (4th ed) 2005,chap. 16 Electrical activity of the heart,chap. 17 Natural excitation of the heart,Observations of Membrane Potentials,4. ACTION PONTIELS,1. IONIC EQUILIBRIA,2. RESTING
2、MEMBRANE POTENTIALS,3. SUBTHRESHOLD RESPONSES,5. 心肌细胞和起搏细胞的动作电位,Observations of Membrane Potentials,Extracellular recording,Intracellular recording,Voltage clamp,macroscopical current,Patch clamp,single channel current,1. IONIC EQUILIBRIA,Electrochemical Equilibrium,When the force caused by the conc
3、entration difference and the force caused by the electrical potential difference are equal and opposite, no net movement of the ion occurs, and the ion is said to be in electrochemical equilibrium across the membrane.,When an ion is in electrochemical equilibrium, the electrochemical potential diffe
4、rence is called as equilibrium potential or Nernst potential.,The Nernst Equation,Where EX equilibrium potential of X+ R ideal gas constant T absolute temperature z charge number of the ion F Faradays number natural logarithm of concentration ration of X+ on the two sides of the membrane,At any memb
5、rane potential other than the Ex , there will be an electrochemical driving force for the movement of X+ across the membrane, which tend to pull the membrane potential toward its EX.,The greater the difference between the membrane potential and the EX will result in a greater driving force for net m
6、ovement of ions.,Movement can only happen if there are open channels!,Distribution of Ions Across Plasma Membranes of a human skeletal muscle cell,2. RESTING MEMBRANE POTENTIALS,The cytoplasm is usually electrically negative relative to the extracellular fluid. This electrical potential difference a
7、cross the plasma membrane in a resting cell is called the resting membrane potential.,The Chord Conductance Equation,where Em membrane potential Es equilibrium potentials of the ion s gs conductance of the membrane to the ion s. the more permeable, the greater the conductance.,The Na+,K+-ATPase cont
8、ributes directly to generation of the resting membrane potential.,All the ions that the membrane is permeable to contribute to the establishment of the potential of the membrane at rest.,细胞膜在静息状态下对K+的通透性一般大于其它离子（主要是IK1），因此大多数细胞的静息膜电位都是胞内为负。,3. SUBTHRESHOLD RESPONSES,The size (amplitude) of the subth
9、reshold potential is directly proportional to the strength of the triggering event.,A subthreshold potential can be either hyperpolarizing (make membrane potential more negative) or depolarizing (make membrane potential more positive),graded potential,This passive spread of electrical signals with n
10、o changes in membrane property is known as electrotonic conduction.,Subthreshold potentials decrease in strength as they spread from their point of origin, i.e. conducted with decrement.,local response,spatial summation & temporal summation,4. ACTION PONTIELS,An action potential is a rapid change in
11、 the membrane potential followed by a return to the resting membrane potential.,action potential of a squid giant axon,At peak of action potential membrane potential reverses from negative to positive (overshoot).,During the hyperpolarizing afterpotential, the membrane potential actually becomes les
12、s negative than it is at rest.,Rising phase (depolarization phase),Repolarization phase,An action potential is triggered when the depolarization is sufficient for the membrane potential to reach a threshold.,Ionic Mechanisms of Action Potential,changes of ion conductance during action potential,Acti
13、on potentials arise as a result of brief alterations in the electrical properties of the membrane.,During the early part of the action potential, the rapid increase in gNa causes the membrane potential to move toward ENa.,The rapid return of the action potential toward the resting potential is cause
14、d by the rapid decrease in gNa and the continued increase in gK.,Action potentials differ in size and shape in different cells, but the fundamental mechanisms underlying the initiation of these potentials does not vary.,During the hyperpolarizing afterpotential, when the membrane potential is actual
15、ly more negative than the resting potential, gNa returns to baseline levels, but gK remains elevated above resting levels.,model of the voltage-dependent Na+ channel,closed,open,inactivated,去极相： INa激活，钠内流,枪乌贼巨轴突动作电位各个时期的主要电流,超级化后电位： 膜电位复极到静息电位时，IK仍然开放，钾继续外流使得膜电位超级化； 随着IK的缓慢关闭，膜电位逐渐回到静息电位。,复极相： INa失活
16、；IK激活，钾外流,Either a stimulus fails to elicit an action potential or it produces a full-sized action potential.,Properties of Action Potential,All-or-None Response,The size and shape of an action potential remain the same as the potential travels along the cell.,The intensity of a stimulus is encoded
17、by the frequency of action potentials.,Refractory Period,relative refractory period,absolute refractory period,Conduction of Action Potential,Local circuit current,Self-reinforcing,myelination,Conduction velocity,diameter,saltatory conduction,5. 细胞动作电位的多态性,心脏中两种细胞的动作电位,心肌细胞,起搏细胞,心肌细胞动作电位的波形,4期：静息期,0
18、期：快速去极化期 -90mV to +30mV,12ms,1期：快速复极化初期 +30mV to 0mV, 10ms,2期：平台期 0mV, 100150ms,3期：快速复极化末期 0mV to -90mV, 100150ms,心肌细胞动作电位的离子机制,心肌细胞动作电位不同时期的主要离子通道,IK1：内向整流钾通道,INa：快钠通道 激活和失活的速率很快,Ica,L：L型钙通道 激活电位约-30mV，激活速度较慢（ 约20ms）， 失活速度很慢（约500ms）,Ito：瞬时外向钾通道 激活（约2ms）和失活（20ms）都相对较快,IK：延迟整流钾通道 缓慢激活和失活（2001000ms），
19、激活后电流随膜电位呈现整流性质,心肌细胞动作电位各个时期的主要电流,1期：快速复极化初期 INa失活；Ito激活，钾外流,0期：快速去极化期 INa激活，钠内流,3期：快速复极化末期 Ica,L逐渐失活，IK进一步激活，钾外流,4期：静息期 IK关闭；IK1电流增强,2期：平台期 Ito失活；IK1通透性降低； IK和 Ica,L激活，钾外流和钙内流相当,IK1的内向整流特性,心肌细胞动作电位的不应期,起搏细胞动作电位的波形,0期：去极化 -40mV to +15mV, 7ms 3期：复极化 +15mV to -70mV, 约100ms 4期：自动去极化 -70mV to -40mV,Ica,T：T型钙通道 激活电位约-50mV， 激活速度很快（约2ms）， 失活速度很快（约2030ms）,起搏细胞动作电位相关离子通道,If：环式核苷酸门控阳离子通道 膜电位从-50mV向超级化变化时缓慢激活 激活后以钠内流为主,起搏细胞动作电位的离子机制,0期： Ica,L激活开放，钙内流 3期： IK激活开放，钾外流 4期： IK关闭，钾外流进行性衰减 If电流（主要是钠内流）进行性增强 后期Ica,L激活开放，少量钙内流,起搏细胞动作电位各个时期的主要电流,