Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
53 Cards in this Set
- Front
- Back
|
What takes most time in postsynaptic delay
|
bring Ca into the Ca channel , takes 1/2 millisecond
|
|
|
What role does Ca play
|
Ca is the trigger for chemical activation
|
|
|
What experiments did Katz do to determine role of Ca
|
if Ca concentration is 0, we predict no transmitter release - no EPP recorded
added Ca of ionophoretic pipette at various times after stimulation - no EPP before stimulation - EPP |
|
|
What did Katz conclude
|
Ca has to be there before stimulation (extracellular)
|
|
|
What happens when you add Mg
|
Mg is a competitive ion, also divalent, will block stimulation (block Ca channel), another blocker - Cd
|
|
|
What other experiments could be done
|
bypass channel to dleiver Ca
|
|
|
Ionophore
|
a molecule that will insert into membrane and create artificial Ca channel
|
|
|
Ca liposome
|
doesnt add pore to membrane, lipid contianing Ca bundles
|
|
|
Caged Ca
|
when you inject free Ca, nothing happens. Molecule bound Ca until hit by light from laser and then loses affinity for Ca and releases it, will get EPP, mimicks how Ca actually gets in, occurs w/out stimulation of nerve or using voltage gated channels.
|
|
|
What is the result of the alternate experiments
|
all 3 result in NT release, so AP not required, just the way to get Ca in.
|
|
|
Ca homeostasis
|
Ca will not make it to active zone inside of cell. 100 nM inside, outside 2 mM. Huge difference between inside and outside. Mechanisms maintain low Ca inside - cant use as signaling molecule if not low inside
|
|
|
Ca/Mg ATPase
|
pump uses ATP as energy supply to pump Ca back out of the cell. Mg needed as cofactor for ATP binding. 1 ATP = 1 Ca out. Pump activated by binding of Ca
|
|
|
Na/Ca pump
|
no need for ATP, uses Na only when concentration is in micro level (very big)
1 Ca - every 3 Na in, doesnt contribute to AP |
|
|
intracellular stores
|
store in ER and mitochondria, liberated by 2nd messenger (Ca, IP3). Organelles sponge up big influx of Ca
|
|
|
Proteins
|
Ca binding proteins work as buffers
|
|
|
Name 2 exogneous buffers
|
EGTA and BAPTA
|
|
|
EGTA
|
relatively slow, high affinity
|
|
|
BAPTA
|
fast, high affinity. Blocks transmitter release, can make it a fluorescent molecule to trace where Ca was bound. To figure out concentration need to combine caged Ca with fluorescent BAPTA
|
|
|
Tetanic potentiation
|
many AP in burst, postsynaptic response summates (accumulating Ca since no time for buffering by homeostasis)
|
|
|
Post tetanic potentiation
|
After giving tetanus - residual Ca
|
|
|
LEMS Lamber Eaton Myasthenic Syndrome
|
autoimmune attack on NMJ's.Patients with small cell lung cancer (neuroendocrine) - similar to neuron - releasing peptides like NT, have Ca channels etc. Immune system making antibodies to proteins - nerve terminal ends up with fewer presynaptic channels then usual. Bind to active zones of Ca channels.50 % of Ca channels lost - get smaller EPP. fewer Ca entry sites, fewer quanta release, so muscle cells do not reach threshold - causes weakness. Exercising helps since Ca is building in the nerve terminal due to residual Ca
|
|
|
Repetitive Neural Stimulation Test
|
connect thumb muscle to electrode, if response gets progressively larger, then suspect LEMS
|
|
|
How would you treat LEMS
|
block K channel, will make AP longer and will get bigger Ca current
|
|
|
2 fold change in Ca concentration would lead to ... change in response
|
2 ^ 4 , or 16 fold change
|
|
|
How can you determine type of Ca channel
|
by blocking with natural toxins
|
|
|
What type of Ca channel is typical for mammalians
|
P/Q
|
|
|
What toxin does P/Q respond to
|
omega AGA IV toxin
|
|
|
Why do we have multiple Ca channel types
|
Each Ca channel unique, Ca channels do not inactivate as well as Na channels, modulation of channel directly by phosphorylation leads to greater plasticity
|
|
|
Ca activated K channel
|
hybrid of voltage gated channel and ligand gated channel, need Ca entering + depolarization, responsible for AHP, if block then no AHP, doesnt return to good driving force, and less Ca entry
|
|
|
What is the purpose of Ca activated K channels
|
abrupt repolarization
|
|
|
How do we know we dont have channels instead of vesicles
|
do whole cell patch clamp, if channel - should see current, Vm didnt change so its not a channel
|
|
|
Freeze fracture technique
|
Heuser Reese, instead of fixing tissue, freeze it, bilayer splits open, looked at presynaptic structure - showed vesicles are fusing
|
|
|
Name 3 evidences for vesicle mediated release
|
freeze fracture, section frozen material, and capacitance change
|
|
|
WHat happens when dephosphorylated synapsin enters
|
release decreased
|
|
|
What happens when inject phosphorylated synapsin
|
nothing no change
|
|
|
What happens when inject CAM kinase II
|
increased release, phosphorylation decreases affinity of synapsin for vesicles and actin
|
|
|
Name 5 cytoplasmic components in fusion
|
1. actin= cytosceleton
2.NSF 3.ATP 4.SNAP 5 Exocyst |
|
|
What is the first step of fusion
|
liberation of vesicle from actin by phosphorylation in storage pool and actin transporting vesicle to release pool
|
|
|
What is the function of RAB 3
|
chaperone protein, removes nsec from syntaxin, allowing formation of core complex
|
|
|
What is core complex
|
VAMP + syntaxin + SNAP 25, same as SNARE proteins, coil together to form " coiled-coil"
|
|
|
Name proteins that are located on vesicle
|
VAMP, synaptotagmin, RAB 3
|
|
|
Name proteins on membrane
|
Ca channel, syntaxin, SNAP 25
|
|
|
Experimental support for the model
|
in vitro binding, competetive peptides, mutations(KO) and toxins
|
|
|
In vitro binding
|
done in test tube, so may not be accurate in body. You either homogenize brain to free proteins in solution or cloned proteins.
1. put syntaxin+ vamp+ snap in test tube 2. add antibody to syntaxin 3. centrifuge 4. run on gel If they are connected, antibodies for one will bring others down as well |
|
|
What happens if you start with nsf alpha snap ATP and add syntaxin, snap 25 and VAMP
|
core complex doesnt form
|
|
|
What is the disadvantgae of in vitro binding
|
doesnt tell about sequence, just what associates with what under various conditions
|
|
|
Competetive peptides
|
interfere with normal binding, stim - EPP normal, stim with peptides NT release decreases, microdimains further from vesicles
|
|
|
What toxins cut core complex proteins
|
tetanus and botulism, they abolish transmitter release - get no EPP
|
|
|
What happens when you knock out RAB 3 gene
|
initially looks normal, with time diminishes, so RAB 3 is helpful but not essential
|
|
|
Why synaptotagmin considered to be Ca sensor
|
1. It has binding sites for Ca - has C2 domains at repeats A and B, binds 4-5 Ca ions, not 1:1 ration but 4 fold
2. also Ca dependent, binds with low affinity, i.e need large amount of Ca to bind - microdomains |
|
|
What did knock out synaptotagmin show
|
that it is responsible for SYNCHRONIZED release
|
|
|
What happens when you remove 1 C2 domain of synaptotagmin
|
release changes from 4 fold to 2 fold
|
|
|
What happens when you change one amino acid in a synaptotagmin sequence
|
remains 4 fold, but shifts to right
|
