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