Comp cells, volume, membrane pot, transporter Flashcards
channels with gates are controlled by what 5 forces? Provide examples
- electric field (membrane pot)
- voltage gated (ie. depolarization)
- Na/K+
- mechanical stimulation (stretching of membrane)
- ie: hair cells in cochlea, touch receptors in skin
- chemical
- synaptic rcptr for nt
- Temperature
- cutaneous thermal rcptr
Ultimately, secondary active transport depends on what?
Metabolism
E is released when Na+ leaks into the cells, captured, and used to pump another ion across membrane.
As opposed to thinking of osmosis as pressure, what is a better way of thinking of it?
Suction.
The quantitative relationship between osmotic suction and pressure one has to exert in order to balance it is proportional to what?
proportional to the difference in solute [ ] on the two sides of the (semi-permeable) membrane
What is the quantitative proportional difference in solute [ ] on two sides of a semi-permeable membrane expressed as?
π=RTΔC
R=gas constant = 8.314J/k mol
or 0.08206 Latm/molK
osmolarity
total [ ] solute particles
Extracellularly vs Intracellularly
tonicity
cell volume (shrink/burst) after diffusion
How do permeating solutes contribute to controlling equilibrium volume of the cell?
it doesn’t.
permeating solutes contributed nothing to controlling equilibrium volume of cell.
(pg 4, noon cell volume).
All that matters is the concentration of nonpermeating solutes which affects movement of water.
a consequence of a permeating solute is that it will/will not exert as large an osmotic force as a nonpermeating solute at the same [ ]
will not
how much the osmotic pressure is diminished
depends on how easily the molecule can cross the membrane.
how much the osmotic pressure is diminished
depends on what?
depends on how easily the permeating solute can cross the membrane.
no osmotic potential: if solute and water cross membranes with equal ease.
half the osmotic pressure: a solute crosses membrane half as easily as water
what is reflection coefficient? its range?
Its a measure of how well the membrane ‘reflects’ the solute
ranges from 0 to 1(non permeating solute)
Are solutes in the ECF permeating/nonpermeating?
Nonpermeating (otherwise cells would lyse)
principle of electrical neutrality
bulk solutions (inside and out) have to be electrically neutral and [cations]i=[anions]i [cations]o=[anions]o total [inside]=[outside]
Na pump properties
- pump is really obligatory coupled Na/K exchange pump
- saturable: demonstrates max rate of activity
(carrier pump, not flux) - pump is electrogenic, not electroneutral, not a 1:1 pump (2 K in, 3 NA out)
- Na/K pump never opened at same time
(channel with 2 gates) - consists of 1 alpha and 1 beta subunit
Na/K pump cycle
- both outside and inner gates are close
- 2 K+ ions inside
- ATP binds, inner gates open, affinity changes from K+ to Na+.
- K+ leaves and Na+ enters.
- ATP is split. leaving pump phosphorylated, and inner gates close
- Outer gate spontaneously opens and affinity changes from Na+ to K+
- Na+ leaves and K enters
- Pump loses its phospate, outer gate closes
describe state of equilibrium
state in which no E is required to move ions across membrane to maintain state
Vm=Eion
(even if [ ] are not same on each side, for every ion in, another will leave w/o ATP)
Diff between equilibrium and steady state
steady state: like equilibrium - ion concentrations arent changing over time, but requires constant input of E (ATP)
Membrane potential depends on relative/absolute permeabilities to ions
relative
What are the differences in Vm between diff cells due to?
- relative permeability of K and Na
- ion concentration
- a small change in K [ ] has a big effect on Ek
What is the driving F of an ion?
the difference between membrane potentials (Vm) and equilibrium potential of that ion (E)
aka the extent to which an ion wants to enter cell
V=IR or I=VG
V is driving force, G is conductance
When Vm=ENa, what is the driving F on sodium?
zero
What is Goldmans equation?
Vm=60log ( [K]o+P[Na]o )
———————
[K]i+P[Na]i
External Na has large/small effects on membrane potential nerves.
External K has large/small effects on membrane potentials in nerves
Na: small
K: large
- nerve and muscle cells are much more permeable to K than other ions
Hyperkalemia
- source of extra potassium
- Important signs
- Strategy 4 treatment
- ICF (98% of all K)
- Compromised Kidney, cardiac arrythmia by EKG
- CBIGK
CBIGK
treatment of acute hyperkalemia in order
C: Calcium: relieve cardiac arrythmias
B: Bicarb: encourages reuptake of K
I+G: Insulin and glucose: juices/fires up Na/K pump
K: kayexalate: ion exchanger with high affinity for potassium.
Kayexalate exchanges Na for K -> removed
Typical volume values for: Plasma ECF ICF Third space
Plasma: 3L
ECF: 13L
ICF: 27L
Third space: 5L
