Lecture 2 Flashcards
Another name for the specific electrical potential (voltage) created by ions in and out of a cell:
Nernst or equilibrium potential for the ion
T or F? Opening K+ channels will depolarize the cell.
F. Hyperpolarize
Will opening the Na+ channels depolarize or hyper polarize the cell?
depolarize
When is there a driving force on the ion to move it in or out of the cell?
When the cell voltage is not the same as the ion’s Nernst potential
Another name for Nernst potential:
equilibrium potential
What factors influence the MP of the cell?
driving force coupled with the ion’s channel conductance
How are the opening and closing of channels regulated?
voltage-gated, ligand-gated, or other factors
Voltage-gated cells rely on:
membrane potential
ligand-gated channels rely on:
chemicals and neurotransmitters
What creates the negative charge inside the cell?
K+ leaving (he also said the Na-K pump contributes little tot the inside negative charge)
What two forces act on ions?
charge and concentration
T or F? At equilibrium there is no flow of ions across the membrane.
F. no NET flow
When is equilibrium reached?
chem force is equal and opposite in direction to the electrical force on the ion
T or F? When a neuron is at resting potential the Na ions are at equilibrium.
F
T or F? When a neuron is at resting potential the K ions are at equilibrium.
F.
T or F? Charged molecules are not subject to a diffusive chemical driving force.
F. applies to all charged and uncharged molecules
T or F? Uncharged molecules are not subject to as electrical driving force.
T.
Another way of saying chemical gradient:
Concentration gradient
What is the diffusion of a specific ion across the PM governed by?
driving force + # of open channels
Is the Na conc high or low inside a typical nerve cell at rest?
low
In which direction do both the chemical and electrical forces go with a typical nerve cell at rest for Na?
into the cell
In which direction do the chemical and electrical forces go with a typical nerve cell at rest for Cl-?
the chemical driving force is directed inside the cell and the electrical driving force is directed outside the cell
In which direction do the chemical and electrical forces go with a typical nerve cell at rest for K?
the chemical driving force is directed outside the cell and the electrical diving force is directed inside the cell
With which molecule are the 2 driving forces complimentary, Na, K, or Cl-?
Na+
With which molecule are the 2 driving forces offset completely, Na, K, or Cl-?
Cl-
With which molecule are the 2 driving forces offset incompletely, Na, K, or Cl-?
K+
T or F? If the concentration gradient for an ion is know, the electrical gradient (voltage) can be calculated.
T. With Nernst Eq.
Is the electrical gradient typically the same as the membrane potential for the cell?
No, only if this is the only permeable ion
In which situation would the electrical gradient be the same as the membrane potential for the cell?
if this is the only permeable ion
Eq. Pot for each ion Nernst eq:
V = (61/n)Xlog(Cout/Cin) (of a given ion) n = ion valence, c = concentration
Nernst potential for Na+ =
+60mV
Nernst potential for Cl- =
-63mV
Nernst potential for K+ =
-90mV
When the membrane conductance increases for a particular ion,:
the membrane potential will move toward the Nernst potential for that ion
In which direction will K+ flow if the cell is at -70mV inside?
out of the cell to try and reach its Nernst potential of -90mV
What are the “n” values for K+, Na+, and Cl-?
+1, +1, and -1
Ion conc.’s in and out of the cell for K+ at equilibrium:
5mM out, 150 mM in
Ion conc.’s in and out of the cell for Na+ at equilibrium:
145mM out, 15 mM in
Ion conc.’s in and out of the cell for Cl- at equilibrium:
108mM out, 10 mM in
Ion conc.’s in and out of the cell for Ca++ at equilibrium:
1 mM out, 0.0001 mM in
In which direction will Na+ flow (in or out) for a neuron resting at -60mV?
in to reach it’s Nernst potential of +60mV
In which direction will Cl- flow (in or out) for a neuron resting at -60mV?
in (very little) to reach it’s Nernst potential of -63mV
In which direction will K+ flow (in or out) for a neuron resting at -60mV?
out to reach it’s Nernst potential of -90mV
What is the driving force for K+ in a cell at -90mV?
zero bc that is the Nernst potential for K+, the cell is at equilibrium
What factors determine the total current produced by a given ion?
driving force and conductance
Equation for current produced by an ion:
conductance X driving force (Vm-Veq)
math symbol for conductance:
g
math symbol for current flow of an ion:
I
T or F? Driving force = Veq - Vm.
F. = Vm - Veq
What is the driving force of K at a RMP of 70mV? Ek = -92mV
-70 - (-92) = +22
2 meanings of conductance:
- conductance of a single channel
2. Cell conductance due to opening of a population of channels
How many channels and how wide the channels are:
conductance
T or F? For a cell at rest, there are few Na+ channels open and many K+ channels open
T
Will a cell have a positive or negative charge if the g(Na) > g(K)?
positive because the conductance for Na+ is greater
Will a cell have a positive or negative charge if the g(Na)
negative bc the conductance for K is greater
Will K flow in or out of a cell if the conductance of K is greater than Na?
out
Will Na flow in or out of a cell if the conductance of K is greater than Na?
in
Will K flow in or out of a cell if the conductance of Na is greater than K?
out
Will Na flow in or out of a cell if the conductance of Na is greater than K?
in
relative influence of sodium channels is:
gNa/(gNa + gK)
relative influence of potassium channels is:
gK/ (gNa + gK)
What channels do you want to open and which do you want to close in order for a cell to depolarize:
Open Na+ and close K+
This ratio controls the MP?
conductance ratio
Is GABA an inhibitory or excitatory neurotransmitter?
inhibitory
Is glycine inhibitory or excitatory?
inhibitory
What effect, if any, will GABA and glycine (separate questions) have on channels?
they both open chloride channels, inhibitin depolarization (- charge enters the cell)
Will opened Cl- channel depolarize or hyperpolarize a cell?
hyperpolarize
Why won’t a cell depolarize when the Na channels are opened after Cl- channels are opened?
Cl- reenters the cell, preventing depolarization
Which has a higher conductance, Cl or Na?
Cl
Which has a higher conductance, Cl or K?
Cl
The opening of Cl- channels will ____ the responsiveness to Na channels.
shunt
The MP of a cell is determined by:
the permeability of each ion (P) and the eq pot. of each ion
Can ions flow against their electrochemical gradient in facilitated diffusion?
No
Which transport ions faster, channels or carriers?
channels
Ions pass through channels based on:
size and charge
T or F? Some channels are very selective while allowing a LOT of that specific molecule to pass
T
T or F? Specificity of channels for ions with the same charge is absolutely specific.
F. ranges from highly specific to relatively non specific
T or F? Cation and anion channels are absolutely specific for charge.
T
T or F? Ligand-gated channels are voltage-sensitive
F
How many times do voltage gated channels span the bilayer?
6-transmembrane
How many domains does a Na channel have?
4
What type of segments does a Na channel have?
6TM
T or F? The tranmembrane segments of the channels are always helices.
F. usually
Which of the 6 segments has a charge on it for voltage sensitive channels?
4th
Do the voltage sensitive channels open when the voltage changes inside or outside the cell.
inside (only?)
Which segement of the channel can move in the membrane and create a pore in the membrane?
5th and 6th
When in the channel is the p loop found?
bw the S5 and S6
T or F? the p loop is a protein
T
Which segments form the gate for the channel?
S5 and S6
This type of channel has one 6-TM peptide:
K channel
How many subunits combine to form the K channel?
4
What structure determines what ions can pass through the channel?
p loop (a protein)
Examples of 6-transmembrane channels:
K+, HCN, cyclic nucleotide (CNG), PKD, TRP, voltage gated Na and Ca channels, polycystic kidney disease (?)
HCN channels are regulated by:
cAMP
CNG channels are regulated by:
cGMP or cAMP
How many segments are require to form the CNG channels?
4, 6-transmembrane proteins
What are CNG channels involve in?
vision and olfaction
What are TRP channels sensitive to?
pH, temp, menthol, capsaicin (hot pepper), sweet bitter and umami taste buds, etc.
Channels both start and end on the (intra/extra) cellular side of the cell
intra
What does ENaC stand for?
epithelial Na Channel
How many subunits is ENaC made of and name?
3 (alpha, beta, gamma)
How many transmembrane segments does each subunit of the ENaC have?
2 and a large extracellular loop
What is required for the ENaC to open?
nothing. constitutively open
What is ENaC involved in?
salt taste in tongue and salt excretion in kidney
2 types of ligand receptors:
Ionotropic and Metabotropic
This type of ligand activated receptor binds the ligand and rapidly activates channel:
Ionotropic
This type of ligand activated receptor binds the ligand and slowly activates channel:
Metabotropic
The channel is part of the receptor in this type of ligand activated receptor:
ionotropic receptor
2 excitatory ligands:
glutamate and AcH
2 inhibitory ligands:
GABA and Glycine
What affect does AcH have on the heart?
slows heart
What type of receptor does AcH use?
G-protein receptor
These are G-protein coupled receptors:
metabotropic
The G-protein may lead indirectly to:
channel activation or modulation
enhance or suppress channel activity:
modulation
most modulators are:
neurotransmitters
What type of channel is the AcH receptor?
ligand-gated channel
What subunits is the AcH receptor made of?
2 alpha, 1 beta, 1 delta (check)
This is a ligand-gated receptor family
Ionotropic AcH, GABA, and Glycine receptors
How many subunits are the Ionotropic AcH, GABA, and Glycine receptors made of?
5 subunits
How many times do the Ionotropic AcH, GABA, and Glycine receptors cross the membrane?
4 times
What forms the pore of the Ionotropic AcH, GABA, and Glycine receptor?
M2
How many times does each subunit of the inotropic glutamate receptor cross the membrane?
3 times, 2nd loop comes back and doesn’t cross all the way
How many subunits form the inotropic glutamate receptor?
4
3 different types of Glutamate Receptors:
AMPA, NMDA, Kainate
how many channels does the GPCR form?
zero
How many transmembrane proteins does the GPCR have?
7
How is the GPCR activated?
ligand activated
What does the GPCR activate inside the cell?
G-protein
What does the GPCR start?
2nd messenger cascade
This type of receptor often regulates a channel:
GPCR
T or F? The GPCR amplifies response to a stimulus.
T
How many subunits is the GPCR made of?
3
The binding of one ligand to a GPCR can lead to the release of _____ of molecules on the other side of the membrane.
1000’s
T or F? ATP is required for stimulation of the GPCR.
F. GTP
Examples of GPCR’s:
sweet taste receptors, bitter taste receptors, umami taste receptors, neurotransmitter receptors
These receptors are involved in autoreceptro feedback:
ionotropic and metabotropic receptors
What affect will glutamate have on a metabotropic receptor?
suppression of voltage-gated calcium channels, negative feedback that controls transmitter release
What affect will glutamate have on a ionotropic receptor?
depolarize synaptic cell
