Ionic mechanisms in repetitive and bursting firing Flashcards
Describe the AP of inhibitory neurons
What does this allow?
SHORT AP
Allows sustained fast firing!
(e.g. Kv3 channels)
What does TEA do?
BLOCKER
- broadens AP
- decreases undershoot
- slows max. firing rate
When may a facilitation of postsynaptic responses occur?
DURING FAST FIRING!
-Results from cumulative INACTIVATION OF Kv CHANNELS
THUS;
-decreases repolarisation rate
-broadens spike
What do SLOW Ca & Kca channels do?
Create RHYTHMIC BURSTING activity
LVA Ca channels available (CLOSED) when:
-mem. potential is LOW (~-65mV or lower)
Inactivate at:
-less negative potentials
LVA Ca channels are often co-expressed in neurons with large conductance (BK)) Kca channels!
- Repetitive bursting at (-) potentials
- Pacemaker firing at mid-range
- Loss of activity during sustained depolarisations
What other effect do Ca & Kca channels have?
Create temporal change in firing activity!
ACCOMODATION mediated by Kca
- accommodation is reversed after the addition of NA
- decreases Kca channel activity
Regulation of Kca by PHOSPHORYLATION
-this decreases their open probability
What do FAST Ca & Kca channels do?
Shape AP repolarisation!
Ca entry thru fast Cav causes activation of BK (Kca) channels
Cav & BK (Kca) channels are CO-LOCALISED in macromolecular complexes
Duration of late-phase (shoulder) depolarisation of AP is INCREASED with a Kca BLOCKER!
What is co-localisation?
Opening rate of Kca channels shows dependence on Ca entry (& depolarisation)!
What factors influence Ca entry at the postsynaptic terminal?
What do these factors regulate?
- DURATION (width) of AP
- FREQUENCY of firing
Regulate:
-types of neurotransmitters released
What does Ca entry through Cav channels form?
Locally high concentrated MICRODOMAINS
Describe the shape of an AP for neurons that release MODULATORY transmitters
BROAD!
What is dynamic voltage-clamp?
A recorded AP waveform is used as the command!
Thus, components of the current can be isolated with blockers or altered ion compositions
Discuss SLOW APs in terms of dynamic voltage-clamping
(Dopaminergic neuron)
- large Ca current during REPOLARISATION
- more Ca entry
THUS, Ca entry controls neurotransmitter release!
Discuss FAST APs in terms of dynamic voltage-clamping
(Purkinje neuron)
Expression of different Na & K channel subtypes changes AP shape
-Cav carry a SMALL amount of Ca current during brief REPOL. phase
(but this is sufficient for small chemical neurotransmitter release!!)
-Nav current DECREASES around peak of AP
The voltage is close to ENa & driving force is minimal
What drives the release of small chemical neurotransmitters?
- LOW frequency stim.
- SMALL Ca influx
What drives the release of chemical AND neuropeptide neurotransmitters?
- HIGH frequency stim.
- LARGE Ca influx
