Lecture 9 - membrane potential and ion transport 1

Question 1

what is the concept of the membrane potential?

Answer 1

Electric force of attraction between opposite electric charges moves them towards one another.
Electric force can be used to perform work.

Separated charges have potential energy
= electric potential
Measured in volts [V] or milivolts [mV]

Ions of opposite sign on either side of a membrane create a membrane potential.

Question 2

what is the resting membrane potential?

Answer 2

All cells under resting conditions have a negative membrane potential

Question 3

what is diffusion?

Answer 3

Net movement of molecules from regions of higher to lower concentration as a result of
their thermal motion

Question 4

what is diffusion of electrically charged molecules?

Answer 4

Driving force [concentration] balances the Driving force [charge]

If:
there is a concentration gradient for X+
the membrane is selectively permeable to X+
Then
there will ALWAYS be an electrical potential across the membrane

Question 5

what is selectively permeable?

Answer 5

If the membrane is 100% selective for K+ the membrane potential will be equal to the equilibrium potential of K+ = EK

Concentration differences for many ions across the membrane, but whether or not they create a membrane potential depends on the permeability of the membrane.

Question 6

are ion channels tuneable conductors?

Answer 6

Channels are proteins
channels can be regulated.
Regulation of channels
changes of ion permeability
change of membrane potential

Question 7

what are action potentials?

Answer 7

Action potentials are generated by transient changes in Na+ and K+ permeability of the membrane due to the opening and closing of Na and K channels

Question 8

how do different ions contribute to the membrane potential?

Answer 8

-Plasma membrane is permeable to both Na + and K +
The membrane potential should be halfway between –90 mV and +60 mV
-But: the plasma membrane is much more permeable for K + than for Na+
- in fact, it contains 50-75 times more K+ channels than Na+ channels
Membrane potential should be closer to –90 mV than +60mV
True: The (resting) membrane potential for a typical neuron is –60mV
The membrane potential is determined by
the equilibrium potential of each ion and
the permeability of the membrane for each ion.

Question 9

How can we calculate the membrane potential?

Answer 9

Nernst  Goldman-Hodgkin-Katz (GHK) equation

GHK takes into account each cation (M+) and anion (A-), their concentration and their permeability across the membrane