Electrical properties of the cell membrane
Transcript of 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