RMP Flashcards
*The RMP results from
The separation of charge across the cell membrane.
Extracellular surface of plasma membrane is …., cytoplasmic surface
Positive, negative.
Why is separation of charge maintained across cell membrane?
Lipid bilayer impermeable to ions, and does not conduct electricity. Hydrophillic heads.
At RMP there is no ….
Net movement of ions.
K+ intra: , K+ extra:
140mM, 5mM
Na+ intra: , Na+ extra:
18mM, 145mM
Cl- intra: , Cl- extra:
5mM, 115mM
Ca2+ intra:, Ca2+ extra:
100mM, 2mM
Nernst Equation:
RT/zF x ln(out/in)
How does ion channel selectivity work?
Oxygen atoms facing inside the channel match and interaction with the hydration shell of the ion, allowing it to be shed so it can diffuse through its concentration gradient.
Why is the flux of K+ out of the cell self-limiting?
Gives rise to PD, makes inside negatively charged, positive K+ ions attracted. (Thus K+ is also subject to electrical driving force).
Ions are driven across the membrane at a rate proportional to … (Vm-Eion).
The difference in membrane potential and equilibrium potential.
At RMP, what exactly balances?
The membrane potential and equilibrium potential. No difference.
$ When the cell is at rest, …. (What is the role of passive ion fluxes on maintaining RMP).
Passive fluxes of ions into and out of the cell through ion channels are balanced, such that the charge separation across the membrane remains constant and the membrane potential is maintained at its resting value.
*Why is RMP not -75 (Nerst p. for K+).
Because open channels in resting cells are permeable to other ion species.
What is chlorine’s movement at rest?
Flows out. Makes inside more positive.
What does the Goldman equation quantify?
The contributions of different ions to the RMP.
Goldman equation:
RT/F x ln{[Pk(K+)o + PNa(Na+)o + PCl(Cl-)i]} / {opposite}
The permeability of the cell membrane for an ion species is proportional to …
The number of open channels that allow passage of that ion.
Goldman equation explained in practical terms:
The greater the concentration and permeability of an ion, the greater its contribution to the RMP.
Why can steady leakage of ions not continue?
Gradients eventually run down.
What is the role of the sodium potassium pump?
Moves ions against their concentration gradients. Extrudes 3Na+, brings in 2K+.
What cardac glycoside inhibits Na+/K+ pump? And what does it do?
Oubain, causes slow depolarisation of membrane.
What are cotransporters?
Use secondary active transport, rely on gradients established by primary active transporters rather than directly using ATP.
What does the NKCC cotransporter do?
Brings Na+, K+ and 2Cl- into cell.
What does the KCC cotransporter do?
Extrudes 1K+ and 1Cl- from the cell.
In immature neurons, which Cl- cotransporter is more active? What does this mean for the intracellular co concentration of Cl-? What does this mean for GABAergic signalling in early development? Why?
NKCC. Cl- conc. higher intracellularly. Means GABA excitatory in early development. Because GABAa receptors are ligand-gated Cl- channels, Cl- flows out the cell instead of in, depolarising.
When is an ion at its equilibrium potential?
When diffusion and electrical forces on the ion are equal.
What does the GHK represent?
Average of Nernst potentials for each permeable ion weighted by their permeabilities.
K+ equilibrium potential:
-90mV.
What are leak channels?
Integral membrane proteins that span the lipid bilayer of the cell membrane.
What does it mean to say that different ions have different hydration shells?
There are different spacings between the water molecules.
What determines intracellular Cl- conc.?
Balance between NKCC and KCC activity.
