GABASYNTHESIS,RELEASE,STORAGE,RECEPTOR

HOW NEUROTRANSMITTER ACT…

GAMMA AMINO BUTYRIC ACID(GABA)

Major inhibitory neurotransmitter in mammalian central nervous system

Present in the nerve terminal

Released from electrically stimulated neurons

GABA functions by binding to specific transmembrane present in plasma membrane

o Molecular formula:C4H9NO2

o GABA is a zwitter ion with deprotonated carboxy group and protonated amino group

SYNTHESIS OF GABA

STORAGE Newly synthesized GABA is stored in synaptic

vesicle by means of vesicular transporter. These are stored at postsynaptic terminal untill

action potential release.

RELEASEo Stored GABA releases into synaptic cleft

stimulated by depolarisation of presynaptic neurons.

o GABA diffuses across the cleft to target receptors on postsynaptic surface.

o The action of GABA is terminated by reuptake of GABA by presynaptic nerve terminals & glial cells

RECEPTORS GABA exerts its effects by two types of

receptors GABA A GABA B

o They differ in their pharmacological & biochemical properties

o GABA A is ionotropic & GABA B is metabotropic

o GABA receptors are channel receptors

GABA A RECEPTOR It has pentameric

structure It has structural

similarity & functional similarity with ligand-gated ion channels

Each GABA A receptor subunit contains two alpha subunit,two beta subnit & one gamma subnit

GABA B RECEPTOR They are hetro dimers Two GABA B subunits

have been cloned b1&b2

B1 subunit has GABA binding site,while B2 subunit interacts with g protein

Two biological action:• decreases ca

2+conductance• increases k+

condctance