Lecture 7 Terms/Questions Flashcards
Equilibrium Potential
- the membrane potential that EXACTLY OPPOSES the steady state electrochemical gradient for an ion
- follows the convention: “inside with respect to outside”
Resting Membrane Potential
- special case of MP where there is steady-state balance b/t active transport & leakage of ions
- for most cells, RMP b/t -20 mV & -90 mV
Na+/K+ ATPase
- pumps 2 K+ ions into cell, removes 3 Na+ ions (uses energy from ATP)
in order to do this:
- hydrolyses ATP (uses energy from ATP)
- several conformational changes (b/c it’s not a channel)
Nernst Equation
the equation that determines the equilibrium potential for a single ion based on the ion concentrations inside & outside the cell
- we can calculate the equilibrium potential for any ion at 37 degrees celsius, given a concentration gradient
Eion = 61/z x log ([ion]out/[ion]in)
Goldman Equation
predicts RMP considering:
- relative permeability of Na+, K+ & Cl-
- the concentrations inside & outside the cell
Electrochemical Gradient
combination of an electrical gradient & chemical gradient
* - ions subjected to an electrochemical gradient will move
Depolarization
more (+)
goes up
Hyperpolarization
even more (-)
goes down
Repolarization
more (-)
dips down more
Relative Permeability
g
Leakage Channel
ion channels that spend most of their time in ?
How do ions cross the cell membrane?
move according to their concentration gradient
& with ATP ases and channels ?
Does RMP represent equilibrium? Why or why not?
no - system is at STEADY STATE where the rate of leakage thru leakage channels is exactly balanced by active transport
NOT equilibrium b/c it requires constant energy!
What kind of channels are responsible for the movement of ions across the cell membrane at RMP?
K+, Na+, Cl- ?
How do these ion channels differ from voltage gated channels?
Ion channels may be specific for one ion or may allow ions of similar size & charge to pass
Voltage channels open and close in response to changes in membrane potential.
?
How do these ion channels differ from ligand gated channels?
Ion channels may be specific for one ion or may allow ions of similar size & charge to pass
Ligand-gated ion channels open when a chemical ligand such as a neurotransmitter binds to the protein.
?
What happens to equilibrium potential for K+ (=Ek) when [K]out increases to 25 mM?
-47 mM
so it depolarizes (more +)
What happens to Ek when [K]out decreases to 2 mM?
-144 mM
so it hyperpolarizes (more -) ?
What happens to Ek when [K]in decreases to 50 mM?
-61 mM
so it depolarizes (more +)
What happens to ENa when [Na]out increases to 175 mM?
+65 mM
so it depolarizes (more +)
What happens to ECl when [Cl-]in increases to 10 mM?
+63 mM
so it depolarizes
What happens to RMP if [K]out decreases to 2 mM?
-89 mV
so hyperpolarization
What happens to RMP if permeability of K (=Pk) decreases to 10?
-63 mV so depolarization (more +)
What happens to RMP if permeability of Na (=Pk) increases to 10,000?
+ 58 mV
(becomes very very +)
goes from 1 to 10 000
What would happen to RMP if there were no leakage channels?
constant @ 0
- all would be 0 in the Goldman Equation
Suppose that there are 1000 K+ leakage channels operating in the membrane & Pk = 75. What would happen to Pk if second messengers opened an additional 1000 channels? What would happen to RMP?
?
What would happen to RMP if the Na+/K+ ATPase was blocked for a short time? For a long time?
establish only RMP @ -80mV
- 1st step transport of 3 & 2 (net loss of +1)
- depolarize b/c stopping electrogenic nature (more (-))
- Na+ & K+ will reach equilibrium eventually b/c nothing moving them back & forth
When patients are rescued from hypothermia, potassium permeability of many cells dramatically increases. K+ leaks from cells into the extracellular fluid (& plasma). Elevated plasma potassium is predictive of a low chance for survival. Why is high serum K+ bad for you? Hint: think about what high K+ does to RMP. What cells need a hyperpolarized RMP in order to function?
d
