Electrical properties of the cell membrane

Electrical properties of

the cell membrane

Transduction of signals at the cellular level

Resting Membrane Potential

Action Potential

Olga Vajnerová

DEPARTMENT OF PHYSIOLOGY

Second Medical School

Charles University

Prague, Czech Republic

Transmission of the signal in NS

EPSP AP

Neurotransmitter

releasing

Transmission of the signal along

the skeletal muscle fibre

Cardiac Electrical Activation

Smooth muscle

Preliminary knowledge

Cell membrane

Na/K ATPase

Ion channels

Cell membrane

Proteins peripheral

integral non penetrating

penetrating (transmembrane)

Phospholipid bilayer

glycerol - fatty acids (hydrophobic)

- fosfate (hydrophilic)

Membrane does exist in the aqueous

environment only.

Cell membrane proteins peripheral

integral non penetrating

penetrating (transmembrane)

Na+- K+ pump

Integral penetrating cell membrane proteins

Na+- K+ pump

Extrudes 3 Na+ ions

Brings 2 K+ ions in

Unequal distribution

of ions

Na+ and Cl - extracelullary

K+ and A- intracelullary

Ion channels

Resting channels - normally open

Gated channels - closed when the membrane is atrest

opening is regulated by

1. Membrane potential (voltagegated)

2. Ligand (chemicaly gated)

3. Membrane potential plus ligand binding (Voltage and chemicaly gated)

4. Membrane stretch(mechanicaly gated)

Integral penetrating cell membrane proteins

Resting (nongated) channels

Potassium leak channel

Gated channels

Voltage gated potassium channel

Two states

Resting (closed) Activated (open) After depolarisation

Three states:

Resting (closed)

After depolarisation

Activated (open)

Inactivated (closed)

Gated channels

Voltage gated sodium channel

Resting membrane potential

Every living cell

in the organism

Membrane potential is not a potential. It

is a difference of two potentials so it is a

voltage, in fact.

When the membrane would be

permeable for K+ only

When the membrane would be permeable for K+ only

Chemical driving forceK+

A-

Na+

Cl-

K+

Outward

movement of K+

Diffusion

When the membrane would be permeable for K+ only

K+ escapes out of the cell along concetration gradient

A- cannot leave the cell

Greater number of positive charges is on the outer side of the membrane

K+

A

i

+

+

+

+

+

-

-

-Na+

Cl-

K+

When the membrane would be permeable for K+ only

electrical driving force

emerges

inward movement of

K+

K+K+

K+

Greater number of positive charges is on the outer side of the membrane

When the membrane would be permeable for K+ only

Chemical

gradient

equals

electrical

gradient

No net

movement of

ions

Steady state is

balanced

Negative membrane

potential

Equilibrium

membrane potential

for potassium

When the membrane would be permeable for K+ only

When the membrane would be

permeable for Na+ only

Na + ???

Cl- ???

Membrane voltage positive ?

null ?

negative ?

When the membrane would be

permeable for Na+ only

Na + influx into the cell

Cl- stay on the outer surface of the membrane

Stabilization of balance – equilibrium membrane potential

for sodium is positive

When the membrane would be

permeable for Cl- only

Cl- ???

Na +???

Membrane voltage positive ?

null ?

negative ?

When the membrane would be

permeable for Cl- only

Cl- influx into the cell

Na + stay on the outer surface of the membrane

Stabilization of balance – equilibrium membrane potential

for chlorine is negative

Equilibrium potential for K+ and Na+

When the membrane would be permeable

for K+ only for Na+ only

How to calculate the magnitude of the

membrane potential

Osmotic work

The work, which must be done to move 1 mol of the substance from concentration Ceto concentrationCi

Ao= R.T.ln [Ce] /[Ci ]

Electric work

The work, which must be done to move 1 mol of the substance across the potential difference E

Ae = E. n. F

R – universal gas constant

T – absolute temperature

Ce , Ci – ion concentration

E – potential difference

n – charge of ion

F – Faraday’s constant

How to calculate the magnitude of the

membrane potential

Ao= Ae

R.T.ln [Ce] /[Ci ] = E. n. F

E =

Nernst equation

E = RT/nF . ln [Ce] /[Ci ]

R – universal gas

constant

T – absolute temperature

Ce , Ci – ion

concentration

E – potential difference

n – charge of ion

F – Faraday’s constant

When the systém is in balance then osmotic work

equals electric work

Resting membrane potential

Membrane permeability

K+ : Na+ : Cl-

1 : 0,03 : 0.1

Goldman equation

Membrane permeability

K+ : Na+ : Cl-

1 : 0,03 : 0.1

Action potential Conductive Membranes:

Axon of neurons

Skeletal muscle fibre

Smooth muscle cell

Heart muscle

Action potential

Membrane permeability

K+ : Na+ : Cl-

1 : 15 : 0.1

Membrane potential

Conductance of the

membrane for Na+ and K+

Depolarization

Achievment of

threshold

Opening of voltage

gated Na + chanels

AP overshoot to

positive values

Terms

- Depolarisation

- Repolarisation

- Hyperpolarisation

Propagation of the action potential along the axon

Propagation of the action potential along the axon

Action potential - propagation without decrement

Action potential - all or nothing law

Time segment when the AP

cannot be elicited

Transmission of the signal in NS

EPSP AP

Neurotransmitter

releasing

Processing of information – local potential (in

receptors)

- Action potentials

Transmission of the signal along

the skeletal muscle fibre

Muscle fiber

axon

Neuromuscular

junction

AP – T tubulus – DHPR receptor – RYR

receptor – Ca2+

Cardiac Electrical Activation

Smooth muscle

Single unit (unitary) –

Nerve fiber -

varicosity

Receptors on the

muscle surface

gap junctions

Multiunit

Questions ???

Comments ???

The endThanks for your attention

The seed was planted