Resting Membrane Potential

Question 1

What is a membrane potential?

Answer 1

Membrane potential is the magnitude of an electrical charge that exists across a plasma membrane and is always expressed as the potential inside the cell relative to the extracellular solution

Question 2

What are membrane potentials measures in?

Answer 2

mV

Question 3

Do animal cells have -ve or +ve resign membrane potentials?

Answer 3

All animal cells have negative membrane potentials at rest

Question 4

Do all cells have an electrical potential across the membrane?

Answer 4

All cells have an electrical potential (voltage) difference across their plasma membrane
• This membrane potential provides the basis of signalling in all types of cells

Question 5

How is membrane potential measured?

Answer 5

The microelectrode - a fine glass pipette - tip diameter is <1um
Very small so it can penetrate cell membrane
Flled with potassium chloride
Because they have the highest conc in cell
-ve potential across membrane
Connect to recorder
No value at beginning
As soon as it penetrates through membrane, voltage drops (see graph)
New level off = resting potential

Question 6

How many minimum essential factors are there for the generation of the membrane potential? What are they?

Answer 6

Asymmetric distribution of ions across the plasma membrane
– (i.e., ion concentration gradients)

Selective ion channels in the plasma membrane
– K+, Na+, and Cl − channels are the most important channel types for most cells; however, there are many cells in which other channels are important as well.

Question 7

What are ion channels?

Answer 7

Proteins that enable ions to cross cell membranes Have an aqueous pore through which ions flow by diffusion and they flow in both directions down their chemical gradient

Question 8

What are the properties of ion channels?

Answer 8

1. Selectivity: for one (or a few) ion species.
   Na+, K+, Ca2+, Cl-, cation channels.
2. Gating: the pore can open or close by a conformational change in the protein
3. Rapid ion flow: always down the electrochemical gradient

Question 9

What are the plasma ion concentrations for a typical mammalian cell?

Answer 9

Sodium - 145 mM
Potassium - 4.5 mM
Chloride - 114 mM
Other anions - 40mM

Question 10

What are the intracellular ion concentrations for a typical mammalian cell?

Answer 10

Sodium - ~10 mM
Potassium - 160 mM
Chloride - 3 mM
Other anions - 167mM

Question 11

How is the resting potential set up?

Answer 11

K+ moving across membrane that sets up membrane potential
K+ moves out based on conc gradt (chemical gradient)
Sets up +ve charge on outside
K+ will want to go back into cell to neutralise charge (electrical gradient)
When two are equal - reach resting membrane potential
When they are equal and opposite there is no net movement of K+ but there is a charge across the membrane as anions dont go through
Membrane is selectively permeable to k+ ions

Question 12

What is the Nernst equation?

Answer 12

The Nernst equation allows you to calculate the membrane potential at which K+ will be in equilibrium, given the extracellular and intracellular K+ concentrations.
For convenience, it is common to work out the constants RT/F and to convert from loge (natural logarithm[sometimes written ln]) to log10: The voltage is given the symbol EK : the K+ equilibrium potential

Can be written for any ion

Question 13

How much k+ os needed to set up a potential?

Answer 13

Barely any moves - 1% change to set up potential

If a membrane is selectively permeable to K+ alone, its membrane potential will be at EK.

Question 14

What is used to treat lactate acidosis?

Answer 14

Treat lactate acidosis with sodium lactate

Bicarbonate is a buffer but will kill them

Question 15

What is the Ek?

Answer 15

The voltage is given the symbol EK : the K+ equilibrium potential

Question 16

What is Ek using intracellular/extracellular K+ values?

Answer 16

-95 mV from Nernst equation

Question 17

What is the resting potential for cardiac and nerve cells?

Answer 17

Cardiac muscle (-80 mV), nerve cells (-70 mV): Resting membrane potential is quite close to EK Not exactly at EK (less negative): membrane not perfectly selective for K+

Question 18

What is the resting potential for smooth muscle cells and erythrocytes?

Answer 18

Cells with lower resting membrane potentials: Somewhat lower selectivity for K+ : increased contribution from other channels,
e.g. smooth muscle cells (-50 mV); erythrocytes virtually no selectivity for K+ (-9 mV)

Question 19

What is the resting potential for skeletal muscle cells?

Answer 19

Many Cl- and K+ channels open in resting membrane
Resting potential ≈ -90 mV
Close to both ECl and EK