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