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M1-C2-L25 --> Passive Ion and Membrane Potential


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Why are proteins necessary to increase permeability?
Ion and other transporters regulate molecule concentrations on each side.
Membrane potential (Vm - voltage of membrane) dependent on what?
K+ permeability
What is resting potential?
-70 mV
What are the four factors contributing to the resting membrane potential?
1. [cations] + [anions] = 0 for both inside and outside cell.
2. Selective permeability due to presence of ion channels.
3. Osmotic neutrality where [solutes]in = [solutes]out
4. Active transport of Na+ and K+
When is Gibbs-Donnan equilibrium achieved?
[solutes] inside = [solutes] outside
Describe the diffusion rate of ion channels and why?
FAST b/c molecules don't bind to anything.
What type of transport channels are always open.
Passive ion channels
Equation for Nernst Eq.
Resting potential on ion

= (RT/zF) ln ([solutes]outside / [solutes]inside)
Equation for membrane resting potential for ions specific in mammal at 37 C.
z 61.5 mV log ([ion]outside/[ion]inside)
Active transport of Na+ and K+ contributes how many mV to the resting membrane potential?
Approx. 3mV
Increasing potassium potential outside the cell will lead to what in Vm? why? What happens to these cells?

b/c Vm seeks more positive Ek

Cells get hyperexcitability
Low potassium concentration outside leads to what? and what physical manifestation?
Hyperpolarization and paralysis
What is the Goldman-Hodgkins-Katz eq.

NOTE Permeability variables and lack of z
Equilibrium potential for sodium
-60 mV
Equilibrium potential for potassium
+90 mV
Equilibrium potential for calcium
+120 mV
Equilibrium potential for chloride
-75 mV
What is the reversal potential?

Max potential due to diffusion of single ionic species
Ratio of K+ inside over outside
Ratio of Na+ outside over inside
Ratio of Cl- outside over inside
Why is the typical resting membrane potential (Vm) a steady state potential and not an equilibrium potential?
Because energy is required to maintain it.

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