1.5. The development of the resting membrane potential. The development and properties of the electrotonic potential. Flashcards
I. Resting membrane potential (Em)
1. What is the definition of Resting Membrane potential (Em)?
potential difference between the intra- and extracellular space when a cell is at rest
-> it is between action potentials, not performing any special functions
I. Resting membrane potential (Em)
2. What are the values of Em for Skeletal muscle, Neuron and RBC? (different cell types)
1/ Skeletal muscle: - 90 mV
2/ Neuron: -70 mV
3/ RBC: - 10 mV
I. Resting membrane potential (Em)
3. What can cause membrane potential deviate from the resting value?
Deviation of the Em can be caused by
- Electrotonic potentials (alterations)
- Action potentials
I. Resting membrane potential (Em)
4. Origin of membrane potential
Origin of membrane potential
- Diffusion potential (appx. 95%)
- Pump potential (3%)
- Donnan potential (2%)
II. Diffusion potential
1/ Definition of diffusion potential
the diffusion potential is any potential (voltage) difference generated across a membrane when an ion diffuses down its concentration gradient
II. Diffusion potential
2/ Characteristics of diffusion potential
1/ Its magnitude depends on the size of the concentration gradient
2/ Its sign depends on the charge of the diffusing ion
II. Diffusion potential
3/ How is diffusion potential made?
1/ Diffusion of charged particles (ions) in water
2/ There is different mobility of diffusing ions results in the generation of diffusion potential
3/ The generated potential gradient retards the diffusion of the positive ions and accelerates the diffusion of negative ions
II. Diffusion potential
4/ An example of diffusion potential
1/ Diffusion potential generated by the diffusion of an HCl (H+ and Cl-) drop in water
2/ There will be a semipermeable membrane (K+ can pass but Cl- and H20 cannot)
3/ K+ transport is driven by the concentration gradient
4/ The generated potential prevents further transport which leads to equilibrium
5/ Therefore, Em stabilizes
III. Equilibrium potential
1/ Definition of Equilibrium potential
equilibrium potential is the membrane potential where the net flow of ions through any open channel is 0
III. Equilibrium potential
2/ Characteristics of Equilibrium potential
1/ Compensates for the chemical gradient of the given ion
2/ Uneven distribution of only a very small quantity/number of ions (charges) is sufficient for the generation of the potential difference (the ion concentrations on the 2 sides of the membrane do not change significantly)
3/ At the equilibrium potential, equal number of the given ions move to 1 direction (driven by the concentration gradient) as to the other direction (driven by electrical gradient) -> lead to dynamic steady state
III. Equilibrium potential
3A. When do we need to use Nernst equation?
If a membrane is permeable to a certain ion, and the ion’s concentration on either sides of the membrane are known
=> its equilibrium potential can be calculated during the Nernst equation
III. Equilibrium potential
3B. What is the formula of Nernst equation?
E : membrane potential (volts)
R: universal gas constant ( ~ 8.31 J/mol/K) T: absolute temperature (oK)
z : charge number (e.g. for K+ is +1)
F : Faraday-constant (~ 96500 C/mol)
III. Equilibrium potential
3C. Validation of Nernst equation?
1/ Permeability only affects the time in which the dynamic equilibrium will be established
2/ Potential difference will not affect the original concentrations
III. Equilibrium potential
4A. What is the Equilibrium Potential of K+, Na+ and Cl- in case of Skeletal Muscle?
III. Equilibrium potential
4B. What is the Equilibrium Potential of K+, Na+ and Cl- in case of Neuron?
III. Equilibrium potential
4C. What is the Relative Permeability of K+, Na+ and Cl-?
IV. Development of resting membrane potential
1. Which factors determine the membrane potential?
1/ The different ion concentrations
2/ The permeability of the membrane to different ions
IV. Development of resting membrane potential
2. What is the general mechanism of development of resting membrane potential?
1/ Resting membrane potential is created as a result of movement of ions across the membrane, down their concentration gradients (established by primary & secondary active transport mechanisms), eager to reach their equilibrium potentials
2/ Each ion ‘’wants’’ to drive the membrane potential toward its own equilibrium potential. Therefore:
-> The movement of ions to which the membrane is most permeable to, will have the greatest effect on the resting membrane potential (in this case K+-ions)
IV. Development of resting membrane potential
3. How do ions participate in the development of resting membrane potential?
1/ The membrane is more permeable to K+ than it is to Na+
=> K+-channels are open and Na+-channels are closed
2/ Equilibrium potential for K+ is -94mV, and since some of them leak out, the membrane potential will also be -94mV
3/ But since some Na+-channels are still open, Na+-ions (+65mV) come into the neuron, which increases the resting membrane potential to -87mV
V. Goldman-Hodkin-Katz equation
1. What is the purpose of Goldman-Hodkin-Katz equation?
For the calculation of the membrane potential
V. Goldman-Hodkin-Katz equation
2. What is the formula of Goldman-Hodkin-Katz equation?
For the calculation of the membrane potential
-> Em is between EK and ENa
V. Goldman-Hodkin-Katz equation
2. Which ions are the main contributors to Goldman-Hodkin-Katz equation?
In many cells, K+, Na+ and Cl- are the main contributors to the membrane potential
V. Goldman-Hodkin-Katz equation
3. What is the formula of Goldman-Hodkin-Katz equation?
For the calculation of the membrane potential
-> Em is between EK and ENa
V. Goldman-Hodkin-Katz equation
4. What is the interpretation of Goldman-Hodkin-Katz equation?
We use the concentrations of ions and their membrane permeability to calculate the membrane potential
- [Cl-]ic is on the bottom, because its charge is negative, and so its driving force direction is opposite to cations-> Cl- will try to leave negative areas and join more positive ones
V. Goldman-Hodkin-Katz equation
5A. What happen if we change the permeability of ions?
it will have effect on Em -> it will go in the direction of the equilibrium potential of the same ion
V. Goldman-Hodkin-Katz equation
5B. If we change the permeability of ions, what are the consequences to the present K+, Na+ and Cl-?
1/ [K+]EC ↑ = depolarization
2/ [K+]EC ↓ = hyperpolarization
3/ pK+ ↑ = hyperpolarization
4/ pNa+ ↑ = depolarization (only change when [Na+]IC)
5/ In case of increase the permeability of Cl- ions, nothing will happen. => Because Ecl (-88mV) is almost the same as Em (-87 mV)
VI. Na+/ K+ - ATPase
1. What is the role of Na+/ K+ - ATPase?
Maintenance of the Em and prevent the concentration equalization of an alive cell
VI. Na+/ K+ - ATPase
2. What is the mechanism of Na+/ K+ - ATPase?
1/ Actively (ATP hydrolysis) transports Na+ and K+ against their concentration gradient -> 3 Na+ are pumped out of the cell, and 2 K+ are brought into the cell
2/ Since there are 3 Na+ exported for every 2 K+ are brought into the cell, the pump makes the membrane potential slightly negative than it would be
3/ The pump maintains the steady Na+ and K+ gradient, which contributes to the movement of the respective ions through leak channels
