浙江大学：膜电位 Membrane potentials

Membrane potentials膜电位 Xia Qiang(夏强),PhD Department of physiology Zhejiang University School of Medicine Tel:88208252 Email:xiaqiang@zju.edu.cn

Membrane potentials 膜电位 Xia Qiang（夏强）, PhD Department of Physiology Zhejiang University School of Medicine Tel: 88208252 Email: xiaqiang@zju.edu.cn

LEARNING OBJECTIVES Describe the maintenance of resting potential in a ce Explain how a cell is induced exciting Contrast graded potentials and action potentials Describe how a cell has refractory phase

LEARNING OBJECTIVES • Describe the maintenance of resting potential in a cell • Explain how a cell is induced exciting • Contrast graded potentials and action potentials • Describe how a cell has refractory phase

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display Distribution of Major Mobile Ions TABLE 6-2 Across the plasma membrane f a Typical Nerve cel Concentration, mmol/L ION EXTRACELLULAR INTRACELLULAR Na 150 15 110 K 5 150 A more accurate measure of electrical driving force can be obtained using mEq/L, which factors in ion valence. Since all the ions in this table have a valence of 1. the mEq/L is the same as the mmol/L concentration

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 difference/mv Ranging from -10 to-100 mv -60 2

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

Overshoot refers to (超射) the development of a charge reversal +60 A cell “ polarized Repolarization is(复极化) because E9g 50> movement back its interior toward the resting potential. Is more negative than its gSN exterior o0 极化) 70 a Resting potential Depolarization occurs Hyperpolarization is when ion Time the development of movement even more negative reduces the charge inside the cell charge imbalance (去极化) (超极化)

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

Equal Extracellular oOoooo00 Cytoplasmic side +, O.9 Source: Barrett KE, Barman SM, Boitano S, Brooks HL Ganong'sReviewofMedicalPhysiologywww.accessmedicine.com Copyright c The McGraw-Hill Companies, Inc. All rights reserved. a membrane potential results from separation of positive and negative charges across the cell membrane The excess of positive charges(red circles)outside the cell and negative charges(blue circles) inside the cell at rest represents a small fraction of the total number of ions present

A membrane potential results from separation of positive and negative charges across the cell membrane. The excess of positive charges (red circles) outside the cell and negative charges (blue circles) inside the cell at rest represents a small fraction of the total number of ions present

The Nernst equation E RT [lon o R=Gas constant ZF Ion ] T=Temperature Z=Valence K+ equilibrium potential (ek)(37C) F=Faraday s constant Ek=6069[K+o(mv) (钾离子平衡电位) K

The Nernst Equation: K+ equilibrium potential (EK) (37oC) i o Ion Ion ZF RT E [ ] [ ] = log R=Gas constant T=Temperature Z=Valence F=Faraday’s constant ( ) [ ] [ ] 60log mV K K Ek i o + + = （钾离子平衡电位）

Compartment 1 Compartment 2 Begin 0.15M 0.15M K in Compartment 2 Nat in Compartment I KCI (b) BUT only K can move K Na Ion movement: Kt crosses into K Compartment 1 Nat Nat stays in Compartment 1 K At the potassium K equilibrium potential buildup of positive charge in Compartment I produces an electrical potential that exactly offsets the K chemical concentration gradient

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. buildup of positive charge in Compartment 1 produces an electrical potential that exactly offsets the K+ chemical concentration gradient. At the potassium equilibrium potential:

Begin Compartment 1 Compartment 2 K in Compartment 2 0.15M 0.15M Nat in Compartment 1 bUt only nat can move Nacl KCI Ion movement (b) Nat crosses into Na+一 Compartment 2 K but K stays in Compartment 2 Na Nat At the sodium K equilibrium potential buildup of positive charge in Compartment 2 produces an electrical potential that exactly offsets the Nat chemical concentration gradient

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. buildup of positive charge in Compartment 2 produces an electrical potential that exactly offsets the Na+ chemical concentration gradient. At the sodium equilibrium potential:

Difference between Ek and directly measured resting potential Ek Observed rp Mammalian skeletal muscle cell -95mV g0 mv Frog skeletal muscle cell 105mⅤ go mV Squid giant axon 96mⅤ -70 mv

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 Difference between EK and directly measured resting potential