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What is the formula for calculating the total current through the membrane?
What is the formula for calculating the total current through the membrane?
In steady state, what equals zero for the membrane?
In steady state, what equals zero for the membrane?
What does the equilibrium potential represent in relation to ionic flow?
What does the equilibrium potential represent in relation to ionic flow?
What is the basis for the direction of transport in the sodium-calcium exchanger?
What is the basis for the direction of transport in the sodium-calcium exchanger?
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How is the energy needed to extrude calcium ions from the cell determined?
How is the energy needed to extrude calcium ions from the cell determined?
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Under what condition can the sodium-calcium exchanger run backwards?
Under what condition can the sodium-calcium exchanger run backwards?
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If 3 ∙ 𝐸𝑁𝑎 − 𝑉𝑀 is greater than 2 ∙ 𝐸𝐶𝑎 − 𝑉𝑀, what occurs?
If 3 ∙ 𝐸𝑁𝑎 − 𝑉𝑀 is greater than 2 ∙ 𝐸𝐶𝑎 − 𝑉𝑀, what occurs?
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What does the variable 𝐷 in the total current equation typically denote?
What does the variable 𝐷 in the total current equation typically denote?
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What is true about the term 𝑉𝑀 in the context of the membrane potential?
What is true about the term 𝑉𝑀 in the context of the membrane potential?
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What does the term 𝐼𝑖 represent in the context of ionic currents?
What does the term 𝐼𝑖 represent in the context of ionic currents?
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What does the Goldman-Hodgkin-Kat (GHK) equation primarily calculate?
What does the Goldman-Hodgkin-Kat (GHK) equation primarily calculate?
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What role does the permeability of an ion play in the GHK equation?
What role does the permeability of an ion play in the GHK equation?
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Which assumption of the GHK model can limit its applicability?
Which assumption of the GHK model can limit its applicability?
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How does the GHK equation account for chloride ions (Cl-)?
How does the GHK equation account for chloride ions (Cl-)?
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What does conductance represent in the context of the membrane?
What does conductance represent in the context of the membrane?
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At which temperature is the constant 58 mV considered in the GHK equation?
At which temperature is the constant 58 mV considered in the GHK equation?
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Which element is NOT a primary ion considered in the GHK equation?
Which element is NOT a primary ion considered in the GHK equation?
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What is the role of the Sodium-Potassium ATPase in maintaining resting membrane potential?
What is the role of the Sodium-Potassium ATPase in maintaining resting membrane potential?
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What determines the energy released by Na+ moving into the cell?
What determines the energy released by Na+ moving into the cell?
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What is the relationship between the reversal potential (VR) and the energy needed to move Ca2+ out of the cell?
What is the relationship between the reversal potential (VR) and the energy needed to move Ca2+ out of the cell?
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How many Na+ ions are transported out of the cell for every ATP molecule hydrolyzed by the sodium potassium ATPase?
How many Na+ ions are transported out of the cell for every ATP molecule hydrolyzed by the sodium potassium ATPase?
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What change does the sodium potassium ATPase cause in the membrane potential?
What change does the sodium potassium ATPase cause in the membrane potential?
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What is the significance of the value of r in the GHK equation?
What is the significance of the value of r in the GHK equation?
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Under which condition does the sodium calcium exchanger run in reverse?
Under which condition does the sodium calcium exchanger run in reverse?
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What type of pump is the sodium potassium ATPase considered to be?
What type of pump is the sodium potassium ATPase considered to be?
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What does the GHK equation represent about the cell membrane?
What does the GHK equation represent about the cell membrane?
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Study Notes
Lecture 7: Resting Membrane Potential II
- Topics: Goldman-Hodgkin-Katz (GHK) Equation, Equivalent Circuit Representation, Sodium calcium exchanger revisited, Sodium Potassium ATPase revisited
Goldman-Hodgkin-Katz (GHK) Equation
- Many charged molecules influence cell membrane electrical properties
- Higher membrane permeability for an ion leads to greater contribution to membrane potential.
- The GHK equation expands the Nernst equation, considering ion permeabilities and concentrations inside/outside the cell.
- The formula is: VM = 58mV * log₁₀ (PK⁺[K⁺]out + PNa⁺[Na⁺]out + PCl⁻[Cl⁻]in) / (PK⁺[K⁺]in + PNa⁺[Na⁺]in + PCl⁻[Cl⁻]out)
- Constants are used in the formula as this version can be seen as using 58mV at 20°C and 62mV at 37°C.
- Note that chloride's movement is reversed as it's an anion.
Goldman-Hodgkin-Katz (GHK) Equation: Assumptions
- Ion movement within the membrane follows the Nernst equation.
- Ions move across the membrane independently.
- The electric field across the membrane is constant.
- This model assumes ions don't interact when crossing the membrane.
Equivalent Circuit Representation of a Membrane
- Biological membranes act like electrical circuits, with voltages (across the membrane), equilibrium, ion currents, and resistance.
- Conductance is the reciprocal of resistance: G = 1/R
- Each ion's current is calculated by multiplying the ion's conductance by the difference between the membrane potential and the ion's equilibrium potential. (I = G*(Vm - E))
- Total current through the membrane is the sum of inward and outward currents.
Equivalent Circuit Representation of a Membrane: Steady-State
- In steady-state, total current through the membrane is 0.
- The membrane potential (Vm) is represented as the sum of ion currents and conductances based on ionic permeabilities and corresponding equilibrium potentials. (Vm = (GK⁺ * EK⁺ + GNa⁺ * ENa⁺ + GCa²⁺ * ECa²⁺ + GCl⁻ * ECl⁻ )/(GK⁺ + GNa⁺ + GCa²⁺ + GCl⁻))
Equilibrium Potential
- Equilibrium potential describes the reversal potential when voltage and direction of ionic current changes.
Sodium Calcium Exchanger
- Moves one Ca²⁺ out of the cell against its gradient for every three Na⁺ into the cell following its electrochemical gradient.
- Can run in reverse: Ca²⁺ enters cell, Na⁺ leaves cell.
- Direction of transport depends on the energy difference between moving Na⁺ inwards vs Ca⁺² outwards.
- The exchanger runs back and forth, regulated by Na⁺ and Ca²⁺ concentration gradients and membrane potential.
- Reversal potential (VR) is when energy released from moving Na⁺ inward equals energy needed to move Ca²⁺ outward. (3*|Ena-VR|=2*|Eca-VR|)
Sodium Potassium ATPase
- Transports Na⁺ out of and K⁺ into the cell.
- For every ATP hydrolyzed, 3 Na⁺ ions are transported out of the cell and 2K⁺ ions are transported into the cell.
- This causes a slight change in membrane potential due to an unbalanced transfer of ions across the membrane.
- The ATPase influences the GHK equation as it affects ion permeability.
- r - A factor that accounts for pumping actions by the ATPase (often has a value of 1.5).
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Description
This quiz covers the Goldman-Hodgkin-Katz (GHK) Equation and its implications for resting membrane potential. Understand the role of ion permeabilities and the equivalent circuit representation. Explore the sodium-potassium ATPase and sodium-calcium exchanger concepts in relation to membrane potentials.
