Physiology 3140A Lecture Notes - Lecture 14: Resting Potential, Reversal Potential, Goldman Equation
2 May 2018
School
Department
Course
Professor
Cell Physiology
Resting Membrane Potential
October 18 2017
Equilibrium potential Calculation for mammalian muscle cell @ 27 degrees:
- Na: +60mV
- Cl: -68 - -39 mV
Resting Membrane Potential
- Equilibrium potential and directions of ionic current flow
- Current-voltage (I-V) relationship
- Goldman equation and resting membrane potential
Why do we need to know the equilibrium potential?
- Equilibrium potential and membrane potential determine the direction and magnitude of ion
movement (current)
- Ohm’s law: V=IR or I =GV
- Ion X is a generic ion in the cell!
o Current passing through this ion, is equal to the conductance (how many channels in the
open state) times the difference between the membrane potential and the equilibrium
potential of this ion
- Conductance = Gz
- Em = membrane potential
- Ex = equilibrium potential for ion x
- Then the membrane potential is GREATER than the equilibrium potential = OUTWARD CURRENT
(POSITIVE)
o Positive ions moving OUT of the cell
- When the membrane potential is SMALLER than the equilibrium potential = INWARD CURRENT
(NEGATIVE)
- When the equilibrium potential is EQUAL to the equilibrium potential = CURRENT IS 0
o No current passing through
- Overall:
o Membrane potential >> equilibrium potential = +
o Membrane potential << equilibrium potential = -
o Membrane potential = equilibrium potential = 0
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Current-Voltage Relationship
- Anything above 0 = positive range, outward current
- Anything below 0 = negative range, inward current
- Reversal potential: current reverses!
o Inward outward
o Outward inward
- The conductance is constant! IT IS NOT CHANGING
- Two important parameters:
o Reversal potential - the membrane potential at which the current is reversed.
o Conductance - the slope of the curve
- Assuming ion x produces the current voltage relationship
- Single type of ion responsible for the current voltage relationship, then the reversal potential and the
equilibrium potential are the same
o THIS IS THE CASE ONLY WHEN ONLY ONE ION IS RESPONSIBLE
o REVERSAL POTENTIAL = EQUILIBRIUM POTENTIAL
- If we use K+ ions as an example:
o IK = GK (Em-EK)
o Em = -65 mV
o EK = -89 mV
o Then, IK = GK [ -65 - (-89)] • = 24 GK
o When Em = -100 mV, IK = -11GK
- If the cell is at -65 mV (where the cell is most commonly sitting at), how big is the current?
o The current Is around 24Gx = positive current
- If the cell is extremely hyperpolarized to -100mV (rarely happens to any cell)
o The same channel’s current goes down, and is now negative
o The current is around -11Gx
- To find the conductance, find the slope (rise/run)
o Rise = current at 0V (y intercept) – 0.8 nA
o Run = reversal potential (x intercept) = -89mV
o CURRENT/VOLTAGE = G
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Equilibrium potential calculation for mammalian muscle cell @ 27 degrees: Equilibrium potential and directions of ionic current flow. Equilibrium potential and membrane potential determine the direction and magnitude of ion movement (current) Then the membrane potential is greater than the equilibrium potential = outward current (positive: positive ions moving out of the cell. When the membrane potential is smaller than the equilibrium potential = inward current (negative) When the equilibrium potential is equal to the equilibrium potential = current is 0: no current passing through. Overall: membrane potential >> equilibrium potential = , membrane potential << equilibrium potential = , membrane potential = equilibrium potential = 0. Anything above 0 = positive range, outward current. Anything below 0 = negative range, inward current. Two important parameters: reversal potential - the membrane potential at which the current is reversed, conductance - the slope of the curve. Assuming ion x produces the current voltage relationship.
