M1 Lec 4 Flashcards
what is the driving force + equation
refers to the force that determines the direction and magnitude of ion movement across the cell membrane.
driving force signs
- a negative current
is a: - a positive current is a:
- inward driving force
- outward driving force
driving force
explain the ionic flow of Na+
* what if the driving force is -125mv
* what if the driving force is +20mv
Na is high outside the cell –> it wants to go inside to follow the gradient
* if driving force is neg: Na wants to go insisde bc attracted to pos (elec gradient) and also follow conc gradient (high to low)
* if driving force is pos: Na kicked out bc repelled by pos (elec gradient) and is kicked out via pump (going against conc gradient)
explain the ionic flow of K+
* what if the driving force is -5mv
* what if the driving force is +20mv
k is high inside the cell –> wants to go outside to follow conc gradient
* if driving force is neg: the inside of the cell is neg enough to attract k back inside the cell (elec gradient) + opposing conc gradient
* is driving force is pos: pos inside repels k and it has to go outside the cell (elec grdient) + leaves to follow conc gradient (high inside to low outside for k)
what did Erwin Neher
and Bert Sakmann develop and what does it do
- patch clamping
- Allows direct recording of currents
through single ion channel
what is the patch clamp method and how does it work
study electrical properties of the cell membrane by measuring currents through membrane
* using glass micropippete that forms a seal with the cell membrane
patch clamp methods: cell attached recording
- pipette remains attached to the intact cell membrane
- the ion channels under patch are studied while the cell remains otherwise undisturbed
patch clamp methods: whole cell recording
* what does it do
* what does it enable us to do
- tight seal ruptures membranes patch under seal. this allows the pipette to access cell interior
- enables recordings of currents from the entire cell membrane
patch clamp methods: inside-out recording
* how does it work
* what does it show
- membrane patch excised from cell by retracting pipette after forming seal
- this exposes the intracellular face to the bath solution
- shows how intracellular molecules regulate ion channel activity
patch clamp methods: outside-out recording
* how does it work
* what does it show
- pipette ruptures membrane and retracts which allows the mebrane to fuse - now the extracellular side of ion channels faces bath solution
- this shows the effects of extracellular ligands and molecules on ion channel activity
how do you measure sodium current
a. set voltage at -20mV
b. measure microscopic sodium current
c. average of microscopic potassium currents
d. macroscopic potassium current
- c and d have similar shapes: this means 1 microscopic current can tell us about all of them
how do you measure potassium current
a. set voltage to +50mV
b. microscopic potassium current
c. average of microscopic potassium currents
d. macroscopic potassium current
* VG k+ has a delay - u can see it
sodium channel structure:
* what is the alpha subunit made up of
* what domain is beta subunit attached to
* which gate lies between domain 3 and
4
* which segment is highly charged
- 4 homolohous domains, each with 6 segments.
- attached to domain 4 (IV)
- loop inactivation gate
- segment 4 (sensitive to voltage)
what is gating charge movement
* outward capacitive current during:
* inward capacitive current during:
movement of gating charge in response to a change in voltage
* depolarization
* hyperpolarization
why are toxins useful in the context of ions
they can be a tool to:
* decipher ion channel function/structure
* can target or isolate certain ion channels
* study channel gating/permeation
* study disease
Tetrodotoxin (TTX)
* what channel does it block
* where does it come from
- blocks VG-Na+
- puffer fish
Tetraethylammonium (TEA)
* what channel does it block
* where does it come from
- blocks VG-K+ channels
- synthetic
What are TRP channels and how can they be gated
Transient receptor potential - ion channels involved in various sensory processes and allow the flow of cations in response to physical or chemical stimuli.
can be gated by:
* temperature
* chemicals
* mechanical force
* voltage
* intracellular molecules
