Membrane Potentials Flashcards
Define membrane potentials.
Difference between electrical charge inside the cell compared to outside
Is membrane potential quantifiable?
YES
- If there are more positively charged ions outside the cell compared to inside, there is an electrical difference since outside is more positive
- This can be measured using a voltmeter in mV
What allows membrane potential to be managed in cells?
Ions donβt move freely through bilayer.
What would occur to membrane potential if a channel protein is inserted into membrane?
- Ions will move down concentration gradient
- EXAMPLE: Movement of positively charged ions out of cell cause inside of cell to become more progressively negative
What can happen if membrane potential rises?
Intracellular changes e.g release of chemicals
Give examples of electrically active cells.
- Neurons
- Muscle cells - contraction occurs upon a change in membrane potential
- Pancreatic cells - alter electrical activity to regulate blood glucose
Ion distribution between intracellular and extracellular space is uneven. What does this allow?
Concentration gradients
Why does potassium favour outward movement?
Intracellular [K+] > Extracellular [K+]
- Moves down concentration gradient
Why does sodium favour inward movement?
Intracellular [Na+] < Extracellular [Na+]
- Moves down concentration gradient
What charge do proteins have? Are they permeable to the membrane?
- Negative
- No
Describe maintenance of resting membrane potential in neurons.
- Mediated by potassium ions out of cell to maintain negative potential
- Permeability is 1
- Relative permeability of sodium is 0.04 and chloride is 0.45
Describe the Gibbs-Donnan effect.
- Positively charged ions move down a concentration gradient until two sides are of equal concentrations i.e chemical potential
- Negatively charged ions will attract positively charged ions in opposite direction to concentration gradient i.e electrical potential
- Ions become unevenly distributed
When is the Nernst equation used?
- Find equilibrium potential
- Opposing forces from the Gibbs Donnan effect are equal so no net movement of ion across membrane
Outline the Nernst equation.
πΈ_π₯=(π π)/(z πΉ) x ln(π_ππ’π‘/π_ππ)
What is the resting membrane potential of a neuron at rest?
-70 mV
If a cell is only permeable to potassium, what would resting membrane potential be expected to be?
- Expected to be close to equilibrium potential of potassium
When would the Goldman-Hodgin-Katz equation be used?
- Cell is permeable to various ions
- Uses relative permeabilities and concentrations of ions to find a cellβs resting membrane potential
What has the largest effect on resting membrane potential?
POTASSIUM - due to its high permeability
Resting membrane potential of a cell is measured to be -75 mV. What contributes to it/
- -70 mV from βleakβ channels - allowing specific ions to move down concentration gradient
- -5 mV from sodium potassium ATPase
How does the sodium potassium ATPase work?
- Uses ATP since ions moved against concentration gradient
- 3 sodium ions moved out of cell in exchange for 2 potassium ions into cell
- Inside becomes slightly more negative than outside
Resting membrane potential is close to equilibrium potential of potassium in neurons. What can be inferred from this?
- Potentials are close - potassium plays role in determining RMP
- RMP slightly more positive than Ek so other ions are involved
In cardiomyocytes, RMP is closer to Ek (iin relation to the neurons)?
- RMP determination is more influenced by potassium ions in cardiomyocytes, compared to neurons
