W3 pre: Ligand gated anion channels - GABA and gycine receptors

Give two types of ligand anion channels

• GABA receptors

• glycine receptors

What do GABA receptors mediate the effects of?

Gamma - Amino Butyric Acid

State the main function of GABA

main inhibitory neurotransmitter in mammal brains

List 3 other agonists for GABA receptors

• barbiturates

• benzodiazepines

• alcohol

What is the main function of glycine

main inhibitory neurotransmitter in the spinal cords of mammals

Give an example of an antagonist for glycine receptors

poison strychnine, which induces seizures

What is the effect of glycine?

motor control - induce hyperpolarisation and reducing neuronal firing

Define ionotropic receptors

binding of a signal to receptor results in change of ion flux into cell

Define metabotropic receptors

binding of a signal to receptor results in a change of enzyme activity within a cell

List 2 types of GABA receptors

A type and B type

GABA-B type receptors

metabotropic (G-protein coupled receptors)

GABA-A type receptors

ionotropic (permeable to Cl- ions)

List the 5 subunits that GABA-A receptors are comprised of and state the structure they form

• α

• β

• γ

• δ

• ε

form a pentameric structure

What do GABA-A receptors share sequence similarity with?

nicotinic acetylcholine receptors

How many genes encode the α subunit of GABA-A receptors?

1-6

How many genes encode the β subunit of GABA-A receptors?

1-4

How many genes encode the γ subunit of GABA-A receptors?

1-4

How many genes encode the δ subunit of GABA-A receptors?

1

How many genes encode the ε subunit of GABA-A receptors?

1

What facilitates ligand binding in GABA-A receptors?

N terminus tail of all subunits

What subunit of GABA receptors are sensitive to ethanol

δ

What facilitates ligand binding in Glycine receptors?

N terminus tail of α subunits

How many glycine molecules are required for channel opening?

3

List the subunits within glycine receptors

• 3α

• 2β

What do phylogenetic analysis of glycine receptors reveal?

that they evolved from GABA-A receptors

How are pores of nAChRs selectively permeable to cations?

negatively charged acidic residues (glutamic acid) are important in conferring selective permeability to cations (sodium)

How are pores of GABA receptors selectively permeable to anions?

positively charged acidic residues (arginine) are important in conferring selective permeability to anions (chlorine)

What is ivermectin?

an anti parasitic agent and insecticide

How does ivermectin exert itself?

by binding and activating glutamate-gated chloride channels in invertebrates

How do inhibitory transmitters cause hyperpolarisation of the post synaptic cell?

triggering an inhibitory post-synaptic potential (IPSP), binding to channels that are permeable to anions

How do excitatory transmitters cause depolarisation of the post synaptic cell?

triggering an excitatory post-synaptic potential (EPSP), binding to channels that are permeable to cations

List two excitatory neurotransmitters

• acetylcholine (neuromuscular transmitter in vertebrates)

• glutamate (main excitatory transmitter in brain)

List two inhibitory neurotransmitters

• GABA

• Glycine

Discuss histamines in humans

act as an inflammatory mediator and neuromodulator that acts on G-protein coupled receptors

Discuss histamines in insects

act as an inhibitory neurotransmitter by causing chloride mediated hyperpolarisation