L5-6 Resting Potential Flashcards Preview

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Flashcards in L5-6 Resting Potential Deck (15):
1


What determines the chemical driving force?

The difference in concentration of molecules across the plasma membrane.

Wchem = - RT ln (Co/Ci)

ln(1) = 0, so if concentrations are equal there will be 0 chem driving force

2

What determines the Electrical Driving Force?

For ions in solutions,
determined by the charge on the ion and the existing
charge across the plasma membrane.

Wel = q (Vi - Vo)

3


What is the Electrochemical Driving Force?

For ions in solution,
determined by adding the electrical driving force to
the chemical driving force.

(determines if ions move in or out)

WEC = Wchem + Wel

4


What is Electrochemical Equilibrium?

For a given ion in
solution, the state at which the electrochemical
driving force is equal to zero
(i.e., the sum of
electrical plus chemical driving forces is equal to 0)

When WEC = 0

5


What is Equilibrium Potential (Ex)

For a given ion in
solution, the membrane voltage at which
electrochemical equilibrium is achieved.

6


What is the Nernst Potential?

Voltage at Electrochemical Equilibrium

EX = 61/z log ([X]o/ [X]i)

z = ion valence

7


What is the electrochemical driving force on K+ at rest?

How could it reach electrochemical equilibrium?

The electrochemical driving
forces on K+ drive K+ out of the cell.

The chemical driving force out is greater than the electrical driving force in.

Electrochemical equilibrium could be reached by increasing the electrical driving force in (hyperpolarize cell so that positive charge is driven in)

For K+  EK = -94 mV (hyperpolarized)

8


What is the electrochemical driving force on Cl- at rest?

How could electrochemical equilibrium be reached?

Cl- is driven out of a cell at rest because the electrical driving force out is greater than the chemical driving force in.

Electrochemical equilibrium could be reached by depolarizing (make less negative) the cell do decrease the electrical driving force out

ECl = -86 mV

9


What is the electrochemical driving force on Na+ at rest?

How could electrochemical equilibrium be reached?

The EC force drives Na+ in, both chemical and electrical driving forces drive Na+ in.

EC Equilibrium could be reached by depolarizing (make less negative) cell do decrease the electrical driving force in.

ENa = +70 mV

10

What is the ion channel current equation?

Iion = gion (Vm - Vion)

I = current

g = conductance

11


What defines Inward Ionic Current and Outward Ionic Current?

Inward ionic current is depolarizing from entering positive ions or exiting negative ions.
Represented on EC Chart with "up arrow" from Vm to Vion

Outward ionic current is hyperpolarizing from entering negative ions or exiting positive ions.
Represented on EC Chart with "down arrow" from Vm to Vion

example: up arrow on Cl- means Cl- is exiting and depolarizing the cell to move towards EC equilibrium

 

12


How would a cell's resting membrane potential be affected by increasing Na+ permeability/conductance?

How would this affect the extracellular K+ concentration and EC driving force?

 

(this is just my interpretation of slide 19)

Increasing a cell's permeability to Na+ would cause more Na+ to enter the cell resulting in depolarization. Less resistance to Na+ inward chemical and electrical driving forces and thus a greater EC driving force in.

Depolarizing the cell would move Vm away from EK, increasing the EC driving force out for K+ thus increasing extracellular [K+]

 

(according to workshop 2 this might not be correct)

13


What is the role of Na-K ATPase?

Pumps out 3 Na and pumps in 2 K, maintains ENa and EK in spite of passive leak of Na and K.

Pumping out a net 1 positive charge / ATP produces a continuous outward ionic current that tends to hyperpolarize the membrane.

14


Summary of Ionic Currents at Resting
Potential:

Equation for sum of all ionic currents?

At resting potential, the total ionic current is zero:
IK + INa + ICa + ICl + IATPase = 0

15


Summary of factors contributing to
Resting Potential:

  1. Intracellular proteins
  2. Ion permeability
  3.  Na-K ATPase
  4. The resting membrane is not at equilibrium. It is in a steady state defined by:

  1. Intracellular proteins are negatively charged at intracellular pH
  2. The resting permeability to K+ and Cl- is  higher than the resting permeability to Na+. Cl- diffuses readily across the plasma membrane such that ECl= EK (Donnan equilibrium). EK is maintained at a constant value by the Na - K ATPase. The relative permeabilities at rest are:
    PK : PCl : PNa
    1.0 : 0.1 : 0.03
  3. The Na - K ATPase pumps out 1 positive charge per ATP hydrolyzed, thus producing an outward ionic current (IATPase).
  4. Steady state defined by:
    Iion = gNa (Vm - ENa) + gK (Vm - EK) + gCl (Vm - ECl) + gCa (Vm - ECa) + IATPase = 0