Resting Membrane Potential Flashcards
What is a membrane potential?
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
What are membrane potentials measures in?
mV
Do animal cells have -ve or +ve resign membrane potentials?
All animal cells have negative membrane potentials at rest
Do all cells have an electrical potential across the membrane?
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
How is membrane potential measured?
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
How many minimum essential factors are there for the generation of the membrane potential? What are they?
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.
What are ion channels?
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
What are the properties of ion channels?
- Selectivity: for one (or a few) ion species.
Na+, K+, Ca2+, Cl-, cation channels. - Gating: the pore can open or close by a conformational change in the protein
- Rapid ion flow: always down the electrochemical gradient
What are the plasma ion concentrations for a typical mammalian cell?
Sodium - 145 mM
Potassium - 4.5 mM
Chloride - 114 mM
Other anions - 40mM
What are the intracellular ion concentrations for a typical mammalian cell?
Sodium - ~10 mM
Potassium - 160 mM
Chloride - 3 mM
Other anions - 167mM
How is the resting potential set up?
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
What is the Nernst equation?
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
How much k+ os needed to set up a potential?
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.
What is used to treat lactate acidosis?
Treat lactate acidosis with sodium lactate
Bicarbonate is a buffer but will kill them
What is the Ek?
The voltage is given the symbol EK : the K+ equilibrium potential
What is Ek using intracellular/extracellular K+ values?
-95 mV from Nernst equation
What is the resting potential for cardiac and nerve cells?
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+
What is the resting potential for smooth muscle cells and erythrocytes?
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)
What is the resting potential for skeletal muscle cells?
Many Cl- and K+ channels open in resting membrane
Resting potential ≈ -90 mV
Close to both ECl and EK
