Lecture 4 Flashcards
Changes in membrane potential
are due to
movement of ions
across the cell membrane
Movement of ions is most often
controlled by the opening and
closing of
ion channels
What do patch clamps measure?
Ion flow - current
What are the 3 types of patch recordings? Explain the difference
Whole cell - strong pulse of suction of the pipette. The cytoplasm is continuous with the pipette interior
Inside-out - expose the intracellular cell to air and cytoplasmic domain is accessible.
Outside-out - retract the pipette, ends of the membrane anneal and extracellular domain is accessible
Voltage-clamp measures
voltage
Current-clamp measures
voltage
Identify examples of when it would be appropriate to use inside-out vs. outside-out patch recordings
Inside-out patch recording: to observe ion channel function after exposing the membrane to intracellular metabolites
Outside-out: to observe ion channel function after exposing the membrane to extracellular ligands
Channels switch between open and closed states almost
instantaneously
inward current is (+) or (-)?
negative
outward current is (+) or (-)?
positive
T/F At rest, single ion channel open time varies, and fluctuates around a mean
open time characteristic of that channel type.
T
What do synaptic or sensory inputs to the neuron change?
-the probability that
the channel will open
-the mean open time
-both
-neither
the probability that
the channel will open
What determines the magnitude of current
flow through an open ion channel?
-single channel conductance of the ion channel (pore
dimensions, charges on channel wall, etc
-Forces causing the ions to move
– Electrical driving force (charge difference)
– Chemical driving force (concentration gradient)
What determines Eion?
Electrical driving force and chemical driving force
What formula calculates the driving force of a current?
Vm-Eion
The difference between the membrane potential and the equilibrium potential of that ion.
What is the current if the membrane potential is at -90 and the Eion is -90?
0 because
I=G(Vm - Eion)
I=G(-90 - -90) = 0
When a positive ion leaves the cell, the current is ?
positive outward
An IV curve measures ?
current through a single channel, plot current as a function of voltage
What does an IV curve do?
Clamping the voltage to different values to see the flow of current as a result.
What does an IV curve tell you?
How the current that flows through that channel changes as you change the membrane potential.
What does a linear/non-rectifying/ohmic IV curve tell you about the conductance?
Conductance is constant throughout all voltage. Flow of current is linear with respect with voltage
How do you find the Eion of a IV curve?
Equilibrium potential is the patch potential when there is no channel current. X=0, look at your y intercept.
How do you find the reversal potential on an IV curve?
X intercept - when current aka I is equal to 0. The membrane potential at which the sign of the current changes.
How would you be able to tell if a channel is permeable to a single ion looking at a IV curve?
Reversal potential is equal to the equilibrium potential of that ion. So if the reversal potential is -70mV, it is permeable to K+ ions because Ek+ is -70mV.
Reversal potential is a property of?
Equilibrium potential?
Membrane potential?
channel
ion
cell
If the membrane potential is equal to the reversal potential, the driving force is
0
What are the 2 types of ion channels?
a) channels activated by physical changes in the cell membrane
b) channels activated by ligands
There are 2 types of channels that are activated by physical changes in the cell membrane. What are they?
voltage-activated and stretch-activated
There are 2 types of channels activated by ligands. What are they?
Extracellular activation and intracellular activation
What is the difference between direct and indirect transmitter action?
Direct - transmitter binds to the ionotropic receptor and the channel opens. Speed is 1 to 1
Indirect - transmitter binds to the metabotropic receptor which sends an intracellular second messenger to the ion channel, allowing it to open. Amplification
Voltage-gated ion channels are activated by?
change in membrane potential
slide 48
