Bio 1-L9-Calcium dependent exocytosis for signal release

resting membrane potential- where is sodium and potassium. how many come in and out?

• sodium- more outside than inside

• potassium- more inside the outside

allows it to do work when gates open- changes polarity

3 sodium in and 2 potassium

what influences if an ion will move

1. chemical- ions will tend to flow down

2. electrical gradient- if negative inside ions will flow down

3. permeability of membrane

4. na/k atpase

what is an action potential briefly

• excitation stimulus- will allow sodium ions to flow into cell

how do ligand gates work? does this cause A.P?

• signal binds to ligand- changes confirmation and it opens- sodium

• channel opens and flow through difussion- inside becomes very POSITIVE- sodium

• inside becomes DEPOLARISED

voltage moves towards neutral- more is needed for action potential though- -55mV

what are the triggers for depolarisation and neurotransmitter release?

• Na is the ELECRICAL- as it changes the voltage- allows Ca2+ voltage channels to open

• Ca2+ is the CHEMICAL for NT. release- changes biochemistry in vesicle

what is the synaptic vesicle cycle steps?

1. active filling of vesicles

2. clustering in active zone

3. docking of these at active zone- attach to Ca2+ channels

4. priming with SNARE complexes

5. calcium triggering fusion

6. recycling

key proteins for neurotransmitter release?

1. VAMPs- v-SNAREs

2. syntaxin- t-SNARE

   synaptotagmin- Calcium CENSOR- binds to C2A and C2B and raises affinity for calcium.

ALL HAVE ALPHA HELICES- pull vesicle down to cell membrane

neurotransmitter release steps

1. sodium gates open- Na

2. cause depolarisation within cell- opens voltage depend Calcium channels

3. calcium flows in

4. synaptotgamin in the active zone bind to calcium

5. causes exocytosis- fusion of vesicles to membrane using SNARE complexes

models of recycling

1. kiss and run- vesicles don’t fully fuse- very quick

2. Clathrin mediated endocytosis- fuse with membrane and new vesicle is made with Clathrin

3. ultrafast endocytosis budding- new vesicle made end-some