Download Anionic proteins are trapped Inside the cell

Changes in electrical gradients
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Electrical disequilibrium
Consequences of electrical disequilibrium
Resting membrane potential
Equilibrium potential
Membrane depolarization and
hyperpolarization
Cell in the body are:
• In chemical disequilibrium
• In osmotic equilibrium
• In electrical disequilibrium – few extra
negative ions inside cells and their
matching positive ions are outside
Na+
Na+
ClClOrganic
Anions
K+
Organic anions
K+
Distribution of main ions
3 Na+
Na+
Na+
ATPase
ClClOrganic
Anions
K+
2 K+
Organic anionsAnionic proteins
K+
are trapped
Inside the
cell
Electrical disequilibrium across the cell membrane
 membrane potential difference
How does electrical charge separation occur?
The cell membrane
Is an insulator
There are more positive charges outside and more negative charges inside
Na+
Na+
ClClOrganic
Anions
K+
Organic anions
K+
Electrochemical gradient
is a combination of the electrical and chemical gradients
Electrochemical gradient
• Electrical gradients and chemical
gradients across the cell membrane
• Electrical force moves K+ into the cell (cell
has more neg. charges)
• Chemical gradient favors K+ to leave the
cell (K+ concentration is low outside)
• These forces reach a steady state
Membrane Resting Potential
• The voltage difference across the cell
membrane when there is an
electrochemical gradient at a steady state
• There is a voltage difference between the
inside and the outside (potential
difference)
The value for the resting
membrane potential
Membrane Potential
• Vm is the membrane potential (millivolts)
• Resting membrane potential for nerves
and muscles is -40 mV to -90 mV
• The resting membrane potential is
determined by K+
K+ channels are open during the
resting membrane potential.
If K+ channels are open.
Equilibrium Potential
• The membrane potential when the channels for
a particular ion are open is called the equilibrium
potential for that particular ion.
• At EK+ the rate of ions moving in due to the
electrical gradient equals the rate of ions leaving
because of the concentration gradient.
• EK+ is close to the resting membrane potential
Factors that are important for the
equilibrium potential for an ion:
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Only channels for that ion are open
The charge of the ion
Concentration of the ion inside the cell
Concentration of the ion outside the cell
At the equilibrium potential for Na+
Artificial cell, Na+ is leaving because the inside became + after the inward
Movement of Na+
Currents during resting membrane
potential
K+ outward current is much stronger than Na+ inward current.
Lots of K+ channels are open, few Na+ channels are open at rest.