第三节细胞的生物电现象 chap. 2 The resting membrane potential chap 3 Action potential from Berne Levy Principles of Physiology (4th ed)2005
• chap. 2 The resting membrane potential • chap. 3 Action potential 第三节 细胞的生物电现象 from Berne & Levy Principles of Physiology (4th ed) 2005
Observations of Membrane Potentials Extracellular recording Oscilloscope ++++++++ 8■|0 50 90七 T Ime ++++++++十 (a) Nerve cell
Observations of Membrane Potentials • Extracellular recording
o Intracellular recording Oscilloscope ++++++++ 8■0 50 ooo Time +++++++++ (b) Nerve cell
• Intracellular recording
● Voltage clamp macroscopical current 51 Omv 60 外向电流内向电流 一膜电流
• Voltage clamp macroscopical current
Patch clamp FBA 膜电流 电极 指令电压 无关电极 细胞膜.灌流液
• Patch clamp
single channel current ww/whA 5pA 20ms
single channel current
1. IONIC EQUILIBRIA Concentration force A B I M ++++++ 0.]M
1. IONIC EQUILIBRIA Concentration force Electrical force
Electrochemical Equilibrium When the force caused by the concentration 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 o When an ion is in electrochemical equilibrium, the electrochemical potential difference is called as equilibrium potential or Nernst potential
Electrochemical Equilibrium • When the force caused by the concentration 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 difference is called as equilibrium potential or Nernst potential
The Nernst Equation RT TI ZF LXIB Where Ex equilibrium potential of X R ideal gas constant T absolute temperature charge number of the ion F Faraday's number Xl natural logarithm of concentration ration [X lOof X+ on the two sides of the membrane
The Nernst Equation B A X A B X X zF RT E E E [ ] [ ] ln + + = − = − Where EX equilibrium potential of X+ R ideal gas constant T absolute temperature z charge number of the ion F Faraday’s number natural logarithm of concentration ration of X+ B on the two sides of the membrane A X X [ ] [ ] ln + +
At any membrane 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 movement of ions Movement can only happen if there are open channels
• At any membrane 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 movement of ions. • Movement can only happen if there are open channels!