Membrane potentials 膜电位

1. Membrane potentials膜电位 Xia Qiang, PhD Department of Physiology Room C518, Block C, Research Building, ZJU School of Medicine Tel: 88208252 Email: xiaqiang@zju.edu.cn

2. Objectives To understand the shape and form of the action potential and understand how it arises in terms of the changes in the underlying Na+ and K+ channels To explore how action potentials are conducted in axons and how this is affected by myelin

3. Electrocardiogram ECG（心电图）

4. Electroencephalogram EEG（脑电图）

5. Electromyogram EMG（肌电图）

6. Extracellular Recording（细胞外记录）

7. Intracellular Recording（细胞内记录）

8. Opposite charges attract each other and will move toward each other if not separated by some barrier.

9. Only a very thin shell of charge difference is needed to establish a membrane potential.

11. Resting membrane potential（静息电位） A potential difference across the membranes of inactive cells, with the inside of the cell negative relative to the outside of the cell Ranging from –10 to –100 mV

12. （超射） Overshoot refers to the development of a charge reversal. A cell is “polarized” because its interior is more negative than its exterior. Repolarization is movement back toward the resting potential. （复极化） （极化） Depolarization occurs when ion movement reduces the charge imbalance. Hyperpolarization is the development of even more negative charge inside the cell. （超极化） （去极化）

13. electrochemical balance - - - - - - - - - - - - - - - - - ++++++++++++++++ chemical driving force electrical driving force

14. The Nernst Equation: K+ equilibrium potential (EK) (37oC) R=Gas constant T=Temperature Z=Valence F=Faraday’s constant （钾离子平衡电位）

15. Begin: K+ in Compartment 2, Na+ in Compartment 1; BUT only K+ can move. Ion movement: K+ crosses into Compartment 1; Na+ stays in Compartment 1. At the potassium equilibrium potential: buildup of positive charge in Compartment 1 produces an electrical potential that exactly offsets the K+ chemical concentration gradient.

16. Begin: K+ in Compartment 2, Na+ in Compartment 1; BUT only Na+ can move. Ion movement: Na+ crosses into Compartment 2; but K+ stays in Compartment 2. At the sodium equilibrium potential: buildup of positive charge in Compartment 2 produces an electrical potential that exactly offsets the Na+ chemical concentration gradient.

17. Difference between EK and directly measured resting potential Mammalian skeletal muscle cell -95 mV -90 mV Frog skeletal muscle cell -105 mV -90 mV Squid giant axon -96 mV -70 mV Ek Observed RP

18. Goldman-Hodgkin-Katz equation

19. Role of Na+-K+ pump: • Electrogenic • Hyperpolarizing Establishment of resting membrane potential: Na+/K+ pump establishes concentration gradient generating a small negative potential; pump uses up to 40% of the ATP produced by that cell!

20. Origin of the normal resting membrane potential • K+ diffusion potential • Na+ diffusion • Na+-K+ pump

22. Action potential（动作电位） Some of the cells (excitable cells) are capable to rapidly reverse their resting membrane potential from negative resting values to slightly positive values. This transient and rapid change in membrane potential is called an action potential

23. A typical neuron action potential Positive after-potential Negative after-potential Spike potential After-potential

24. Electrotonic Potential（电紧张电位）

25. The size of a graded potential (here, graded depolarizations) is proportionate to the intensity of the stimulus.

26. Graded potentials can be: EXCITATORY or INHIBITORY (action potential (action potential is more likely) is less likely) The size of a graded potential is proportional to the size of the stimulus. Graded potentials decay as they move over distance.

27. Graded potentials decay as they move over distance.

28. Local response（局部反应） • Not “all-or-none” （全或无） • Electrotonic propagation: spreading with decrement（电紧张性扩布） • Summation: spatial & temporal（时间与空间总和）

29. Threshold Potential（阈电位）: level of depolarization needed to trigger an action potential (most neurons have a threshold at -50 mV)

30. Membrane potentials膜电位（续） Xia Qiang, PhD Department of Physiology Room C518, Block C, Research Building, ZJU School of Medicine Tel: 88208252 Email: xiaqiang@zju.edu.cn

31. Objectives To understand the shape and form of the action potential and understand how it arises in terms of the changes in the underlying Na+ and K+ channels To explore how action potentials are conducted in axons and how this is affected by myelin

32. Review Intracellular and extracellular recording Resting membrane potential (definition and mechanism) Action potential (definition) Local response (Graded potential) Threshold potential

33. Ionic basis of action potential

34. Nobel Prize in Physiology or Medicine 1963 • "for their discoveries concerning the ionic mechanisms involved in excitation and inhibition in the peripheral and central portions of the nerve cell membrane" • Eccles Hodgkin Huxley • Voltage Clamp

35. Nobel Prize in Physiology or Medicine 1991 • "for their discoveries concerning the function of single ion channels in cells" • Erwin Neher Bert Sakmann • Patch Clamp

36. From: doi: 10.1111/j.1469-7793.2000.t01-1-00593.x June 15, 2000 The Journal of Physiology, 525, 593-609 Figure 2 Instantaneous I–V data reveal that IK has a more hyperpolarised reversal potential than IA A, tail current family for IK, recorded in 5 mM 4-AP. Following a 100 ms step to +53 mV, the membrane potential was stepped to a level ranging from +53 to -117 mV in 10 mV increments. Each trace is an average of 12 interleaved episodes. Leak currents have been subtracted. B, plot of peak instantaneous IK, from extrapolated exponential fits to the tail currents (Methods), versus tail potential for this patch. The superimposed curve is a quadratic polynomial. The reversal potential for this patch was -86.4 mV. C, tail current family for IA, recorded in 30 mM TEA and shown expanded in the inset. The pulse protocol was as in A, except the duration of the prepulse to +53 mV was 1.5 ms. Each trace is an average of 6 interleaved episodes. Leak currents have been subtracted. The slowly rising trace in the inset is the estimated time course of the contaminating IK at +53 mV in this patch. At 1.5 ms the contamination is about 10 % of IA. D, plot of peak instantaneous IAversus tail potential for this patch. The fitted quadratic polynomial gives a reversal potential of -68.7 mV.

37. Blocker: Tetrodotoxin (TTX) (1) Depolarization（去极化）: Activation of Na+ channel (2) Repolarization（复极化）: Inactivation of Na+ channel Activation of K+ channel Blocker: Tetraethylammonium (TEA)（四乙胺）

39. The rapid opening of voltage-gated Na+ channels explains the rapid-depolarization phase at the beginning of the action potential. The slower opening of voltage-gated K+ channels explains the repolarization and after hyperpolarization phases that complete the action potential.

42. An action potential is an “all-or-none” sequence of changes in membrane potential. The rapid opening of voltage-gated Na+ channels allows rapid entry of Na+, moving membrane potential closer to the sodium equilibrium potential (+60 mv) Action potentials result from an all-or-none sequence of changes in ion permeability due to the operation of voltage-gated Na+ and K + channels. The slower opening of voltage-gated K+ channels allows K+ exit, moving membrane potential closer to the potassium equilibrium potential (-90 mv)

43. Mechanism of the initiation and termination of AP

44. How to re-establish Na+ and K+ gradients after action potential ? Concentration gradient of Na+ and K+ Extracellular (mmol/L) Intracellular (mmol/L) Na+ 150.0 15.0 K+ 5.0 150.0

47. For a television game show, 16 contestants volunteer to be stranded on a deserted island in the middle of the South China Sea. They must rely on their own survival instincts and skills. During one of the challenges, one team wins a fishing spear. They catch a puffer fish and cook it over the open flames of their barbecue. None of them are very skilled in cooking, but they enjoy the fish anyway. One of the contestants, a worldwide traveler, comments that it tastes like Fugu. After dinner, they all develop a strange tingling around their lips and tongue. They all become weak, and their frailty progresses to paralysis. They all die. What is the mechanism of toxicity? • A Blockage of the sodium gates • B Blockage of the potassium gates • C Interference with the release of acetylcholine • D Antibody directed against the acetylcholine receptor • E Maintaining the sodium channel in an open state

48. For a television game show, 16 contestants volunteer to be stranded on a deserted island in the middle of the South China Sea. They must rely on their own survival instincts and skills. During one of the challenges, one team wins a fishing spear. They catch a puffer fish and cook it over the open flames of their barbecue. None of them are very skilled in cooking, but they enjoy the fish anyway. One of the contestants, a worldwide traveler, comments that it tastes like Fugu. After dinner, they all develop a strange tingling around their lips and tongue. They all become weak, and their frailty progresses to paralysis. They all die. What is the mechanism of toxicity? • A Blockage of the sodium gates • B Blockage of the potassium gates • C Interference with the release of acetylcholine • D Antibody directed against the acetylcholine receptor • E Maintaining the sodium channel in an open state

49. Conduction of action potential（动作电位的传导） Continuous propagation in the unmyelinated axon

50. Saltatory propagation in the myelinated axon http://www.brainviews.com/abFiles/AniSalt.htm