Unit 2: cell wall/membrane potential Flashcards
in a test tube with two compartments separated by a SEMI permeable membrane, the left compartment contains SOLUTE and the right side just contains water. explain the differences in osmolarity and water concentration for each side.
left side:
a high osmolarity
a low [water]
right side:
high [water]
what is H2O’s normal concentration gradient?
flows from areas of high [ ] to low [ ]
explain the role of osmotic pressure in regards to a test tube with a semi-permeable membrane
the opposing force against osmosis to keep the test tube leveled
the pressure required to prevent osmosis from occurring through a semipermeable membrane
1 mOsm = _____ mmHg in 1L
19.3 mmHg
GLUT-4 facilitated diffusion transport proteins are found primarily in
muscles and fat
GLUT-1 facilitated diffusion transport proteins are found primarily on
RBCs
(and neurons)
compare and contrast facilitated vs simple diffusion speeds
the rate of simple diffusion increases linearly with increases in [ ] gradient
+ occurs linearly because there is no conformation change of the protein
the rate of facilitated diffusion increases with increased [ ] gradient UNTIL all transporter proteins are saturated
+ conformational change speed can only go so fast
+ rate of facilitated diffusion plateaus at this point (Vmax, AKA the max speed at which conformational change occurs)
list other factors that impact the rate of diffusion
concentration of molecules inside vs outside
+ the bigger the difference, the faster something can diffuse
membrane (lipid) solubility
+ increased lipid solubility = more diffusible through cell wall
size of particle
+ smaller = easier than larger particles to diffuse
size of pores
temperature
+ the higher the temp the faster they can diffuse
physical pressure
+ blood pressure
electrical charge
+ electrochemical gradient
chemical gradient
Where does the Na+/K+ ATPase pump move Na+? And how many Na+ molecules?
3 Na+ OUT of cell
Where does the Na+/K+ ATPase pump move K+? And how many K+ molecules?
2 K+ IN to the cell
How much ATP is required to move Na+ and K+ through the Na+/K+ ATPase pump?
1 ATP molecule
Why does the Na+/K+ ATPase pump require energy?
it moves Na+ and K+ AGAINST their natural concentration gradients
ECF [Na+] > ICF [Na+]; it is pumping Na+ OUT of the cell where it is ALREADY high in [ ]
ECF [K+] < ICF [K+]; it is pumping K+ INTO the cell where it is ALREADY high in [ ]
what is the net charge inside of the cell when using the Na+/K+ ATPase pump?
3+ out and 2+ in would result in a net charge loss of -1
what is the net ION loss of the cell when using the Na+/K+ ATPase pump?
net ion loss = -1
2 K+ in and 3 Na+ out = -1
how does the Na+/K+ ATPase pump “diurese” the cell?
as the pump moves Na+ out of the cell, H2O will follow
this pump maintains the intracellular volume inside the cell
how might intracellular edema occur?
if the Na+/K+ ATPase pump is “shut down”, intracellular edema may occur
(i.e. ATP is depleted in cell > pump dysfunction > intracellular edema may occur because of the accumulation of sodium and water inside the cell)
the only way to “fix” this is to fix the ATP issue
where does the sodium and water come from in regards to using the Na+/K+ ATPase pump to pump out Na+ and H2O?
water may have “snuck back in” via other channels
the extra sodium comes from various secondary active transport proteins (i.e. NCX allows 3 Na+ in and pumps 1 Ca2+ out)
Na+ is also able to diffuse through the cell at rest
Na+ can also enter the cells during action potentials
explain what the Na+ and Ca2+ levels would be inside of a cell if this particular cell has a DYFUNCTIONAL Na+/K+ ATPase pump and a functional NCX.
a dysfunctional Na+/K+ ATPase pump means that there would be an increased [Na+] inside the cell (because Na+ is not getting pumped out) as well as an increased [Ca2+] inside of the cell (because the NCX would not be exchanging as much Ca2+ out for Na+ in due to the already increased [Na+] inside the cell).
excitable cells are ________ charged at rest and when activated they become briefly ________ charged
negatively; positively
how do proteins influence the resting membrane potential?
there are more proteins inside the cell than outside
proteins carry a net NEGATIVE charge because of the charge of amino acids (net - charge)
what is the nernst potential equation (aka the equilibrium potential)
EMF (mV) = -/+ 61 x log ([in]/[out])
(+ 61) if the ion is an anion (-)
(-61) if the ion is a cation (+)
what does the nernst potential/equilibrium potential represent?
the voltage that will prevent ions from diffusing across the membrane, down their concentration gradients
it predicts the charge of the cell if it allowed ONE ION across the cell wall
what does the goldman equation (GHK) represent?
the overall membrane potential factors in equilibrium potentials that the cell is permeable to (Na+, Cl-, K+, etc.)
what is the overall membrane potential on a typical cell?
-80mV (closer to the equilibrium potential of K+, which is around -91 mv)
this takes into account that a typical cell is very permeable to 2 ions: Na+ (60 mV) and K+ (-91 mV)
explain what the membrane potential would be if there was an influx of sodium into the cell?
if there was an influx of sodium into the cell, the membrane potential would approach a number more closely resembling that of the permeability of Na+
nernst potential for Na+
61 mV
nernst potential for K+
-90mV
what is the permeability ratio of K+ to Na+
K+:Na+
10:1
what is the equilibrium potential of a cell at rest (resting membrane potential)
-80 mV
(closer to K+ membrane potential)
what is a “leak” channel
these gates “leak” ions into the cell constantly; they’re open all the time
ex) Na+ “leak” channel
if you have a hyperkalemic patient (ECF [K+] = 8.0), what would you expect would happen to the movement of potassium through the cell? what if the ECF [K+] was 2.0?
since the [ ] gradient has decreased, the movement of potassium out of the cell will be slower (when K+ = 8)
when K+ = 2.0, the potassium would move much quicker out of the cell since the [ ] gradient is larger
what would you expect would happen to cellular function if your [Na+] was normal, but your ECF [K+] high?
since your [K+] is high, your equilibrium potential of K+ is going to be a less negative number than normal (e.g. -70 mV versus a normal value of -90 mV)
since your [Na+] is normal, your Na+ equilirbium potential is still going to be +60mV; however, your RESTING MEMBRANE potential is now going to reflect the change in [K+], which would mean your new Vrm would be less negative (e.g. -60 mV vs a normal value of -80 mV)
when your Vrm is abnormal, cellular function is abnormal (more/less excitable cells, cardiac issues d/t cells being more permeable to K+, etc.)
at rest cells are _________ charged
negatively
depolarized
cell becomes less polar
cell becomes more POSITIVELY charged OR less negative
“stimulated or turned on”
repolarization
to return to vrm (normal resting polarity)
to become more NEGATIVE after AP
AP = action potential
hyperpolarized
either at rest or after AP:
the cell becomes more polar
the cell becomes more NEGATIVELY charged than it is at rest
dips below normal vrm
action potential
propogation of electrical signal through the length of a cell
what is driving force?
some ions want to move across the cell wall at different speeds depending on what is going on inside of the cell
driving force is dependent on 3 factors:
- the charge of the ion
- the [ ] gradient of the ion
- charge inside the cell (vrm)
the vrm is -80 mV. assume all normal ICF & ECF ratios inside of the cell – amongst the 3 ions (K+, Na+, and Ca++), rank the ions in order of highest to lowest driving force
- Ca++
- Na+
- K+
Ca2+ has the highest [ ] gradient, and a double positive charge.
what does the equilibrium potential mean?
the charge required on the inside of a cell to prevent the net movement of a particular ion
ex) 60 mV = Na+
ex) -90 mV = K+
if these membrane potentials are equal to the equilibrium potentials of their respective ions, that would stop the net movement of that particular ion
if there are many more “leaky” K+ channels in a cell, why will the K+ not overly migrate out of the cell?
the cell at rest has a very negative charge (-80mV)
in contrast, sodium will not overly get drawn into the cell because there are fewer “leaky” sodium channels present on the cell at rest
what drives membrane potential to a negative number if there is not a lot of net movement of ions at rest?
the membrane does not require CURRENT; it just requires the POTENTIAL for current (open pathways/leaky channels = the POTENTIAL for current) hence, membrane POTENTIAL
if you have ion X-, and its equilibrium potential is -50 mV, what would the [ ] gradient be for this ion?
what if the overall membrane potential was -80 mV? what would the net movement of X- be now?
the [ ] would be higher OUTSIDE the cell than INSIDE; X- would want to move INSIDE the cell
-50mV is the cell’s membrane potential to prevent X- across the cell wall
if the overall membrane is -80 mV, the net movement of X- would now move OUT of the cell because -80 mV is more NEGATIVE than -50 mV (past the point of repelling the ion)
at rest, what conformation is the fast Na+ channel in?
the activation gate (m-gate) is closed and the inactivation gate (h-gate) is open
at what point during the action potential does the activation AND inactivation gate open on a voltage gated Na+ channel?
depolarization at the THRESHOLD POTENTIAL
what is the difference between voltage-gated Na+ channels vs “leaky” Na+ channels?
voltage-gated Na+ channels only open/close when the threshold potential is met
leaky Na+ channels are always open
these type of drugs act at the voltage-gated Na+ channels
-caine derivatives
once the inactivation gate of the Na+ channel is closed, this process must first happen before the Na+ channel can go back to its normal resting state
repolarization
list out the phases of a voltage gated Na+ channel during an action potential
- resting state: activation gate CLOSED; inactivation gate OPEN.
- threshold potential met and cell DEPOLARIZES.
- Na+ channel has BOTH GATES OPENED very briefly; Na+ influx into the cell. activated state.
- inactivation gate very quickly CLOSES; activation gate still OPEN. repolarization has initiated. inactivated state.
- activation gate CLOSES. inactivation gate OPENS. cell is now “re-set” and VG Na+ channel goes back to resting state.
what two things must occur first so that VG Na+ channel can “reset”
- activation gate must close (FIRST)
- inactivation gate must REOPEN
+this must be done in this order so that Na+ does not flood into the cell while the VG Na+ channel is trying to reset
VG Na+ channel resting (mV)
-90 mV
VG Na+ activated state (mV)
-90 mV to +35 mV
VG Na+ inactivated state (mV)
+35 mV to -90 mV
VG K+ channels are _____ to open and _____ to close. Why?
they’re slow to open and slow to close
if they all opened right away, this would interfere with the membrane potential and it would interfere with the action potential
structurally, how are VG Na+ and K+ different?
VG Na+ has 2 gates
VG K+ has only 1 gate (the gate is on the inside of the cell)
list out the phases of a voltage gated K+ channel during an action potential
- at rest, the VG K+ channel’s gate is closed (-90mV)
- the VG K+ gate opens once depolarization occurs and it opens very slowly allowing a slow EFFLUX of K+
- because these VG K+ channels are slow to close, there will be a dip below the vrm (hyperpolarization) until it reaches back to normal vrm
why would a person with hyperkalemia have poor cardiac conduction?
if your ECF K+ is higher, your [ ] gradient for K+ is smaller, meaning your equilibrium potential for K+ will also be less negative
when your equilibrium potential for K+ is less negative than a normal -90mV, this will cause your overall vrm to also be less negative (-71 mV)
so if your vrm is less negative, the number of available VG Na+ channels decreases, resulting in a slower influx of Na+ and a slower impulse conduction
