Week 03 Lects 1+2 Memb. Potential, Ion Channs, APs Flashcards
What is the general range of membrane potentials (Em)?
-90 to +20 millivolts
What is the general range of the resting membrane potentials (ER)?
This differs by cell type… what are the extreme examples?
What cells have an RMP at their most negative value?
general range: -90 to -10 mV
Examples:
- Low: Skeletal muscle = -90 mV
- High: RBCs = -10 mV
- Pacemaker Cells (heart nodes, smooth muscle) have their RMP at their most negative values.
What is diffusion potential?
What does its amplitude depend on?
And its “sign” (+/-) ?
- potential difference across a membrane generated by a concentration difference a permeating ion
- amplitude depends on size of concentration gradient
- sign depends on charge of the ion
What is equilibrium potential?
What force slows and then stops the flow of ions down their concentration gradient in order to achieve equilibrium potential?
Equilibrium potential is the diffusion potential that exactly opposes the tendency for diffusion caused by a concentration difference.
The electrical gradient caused by the initial concentration gradient-driven diffusion of an ion eventually stops net diffusion to achieve equilibrium.
How can equilibrium potential of an ion be calculated?
Nernst Equation
Eion = -60/Z · log (C1/C2)
Z = charge of the ion
C1/2 = concentrations of ion on either side of membrane
What is the skeletal muscle intracellular concentration of K+?
Na+?
Cl-?
K = 150 mM
Na = 12 mM
Cl = 4 mM
What is the skeletal muscle extracellular concentration of K+?
Na+?
Cl-?
K = 4 mM
Na = 145 mM
Cl = 120 mM
How do the permeabilities of K+, Na+ and Cl- compare for a skeletal muscle?
K+ is ten times more permeable than Cl- which is ten times more permeable than Na+.
P (cm/s):
- K+ = 5E-7
- Cl- = 5E-8
- Na+ = 5E-9
What are the equilibrium potentials of K+, Na+ and Cl-?
- K+ = -94 mV
- Na+ = +65 mv
- Cl- = -88 mV
How is the the membrane potential of a cell calculated considering multiple ions?
Goldman Hodgkin Katz Equation
(AKA Chord Conductance Equation)
Em = -60 times log of [(sum of ions’ permeabilities times their IC conc.) divided by (sum of ions’ perm. times their EC conc.)]
- NOTE: for negative ions EC conc. are on top (dividend) of logarithmic expression
Why can we ignore the data regarding sodium and chloride ions when calculating membrane potential of a skeletal muscle cell with the GHK equation?
Because their permeabilities are significantly lower than that of potassium.
What happens to the membrane potential as the permeability of a certain ion increases?
It approaches the equilibrium potential of that particular ion.
What happens when the permeability of the chloride ion increases in skeletal muscle cells?
Why?
Rather than changing drastically, the membrane potential simply stabilizes.
Because the equilibrium potential of Cl- is so close to the resting membrane potential.
In an example of Na/K-ATPase inhibition, what accounts for the initial slight depolarization of the cell when the pump is first inhibited?
Pump Potential
- a 3-5% depolarization due to the loss of the pump function, which had been constantly carrying a net +1 charge out of the cell
( remember: NA/K-ATPase = 3 Na+ out per 2 K+ in )
In an example of Na/K-ATPase inhibition, what accounts for most of the depolarization seen upon inhibition of the pump?
The high diffusion potential of K+ ions causes the potassium excess in the cell to equalize and 90-95% of the observed depolarization.
