Neuronal signalling mechanisms (HISTORY)

Question 1

Receptors

Answer 1

G protein coupled receptors - metabotropic receptors.
Ionotropic receptors - Ligand gated ions channels, ligand binds to outside of channel, channel opens.

Question 2

Early history

Answer 2

Before 1860 no idea about how drugs would mechanistically work on cells.
After 1860 the systematic analysis of drug - cell interaction began.

Question 3

John Langley

Answer 3

Mid 1870s - used plant extract alkaloid (pilocarpine) on salivary gland - saliva production increased.
Late 1880s - studies on nicotine, on gland and muscle, saw contraction.
Lewandowski - suprarenal extract - eyes dilated.

Question 4

Neuroadrenaline and acetycholine

Answer 4

Nadrenaline only works on metabotropic receptors.
Acetycholine binds to ionotropic and metabotropic.

Question 5

1905 Fowl experiment

Answer 5

Crushed leg of bird, injected nicotine, muscle contraction observed.
Blocking contraction with curare - electrical stimulation could still cause muscle contraction. He said an ‘accessory substance’ received stimuli - receptive substance.

Question 6

A V Hill

Answer 6

Expressed receptor theory quantitatively and mathematically represented it.
y = N/k’+kN - M
Hill equation
won the nobel prize

Question 7

Schild

Answer 7

Used agonist and antagonist drugs to quantify receptor features and equilibria of reactions. Schild plot is at the core of pharmacology.

Question 8

Ahlquist
Black

Answer 8

Different chemicals eg dopamine serotonin had different effects on different body systems - thought it must be due to differences in receptors.
Black then developed beta blockers - won nobel prize.

Question 9

Sutherland
Rodwell

Answer 9

sutherland Applied adrenaline to liver cells - another substance was built up before glycogen hydrolysis - he called it ‘second messenger’.
Rodwell proposed 3 step model in which G proteins mediate agonist receptor interaction.
Nobel prize

Question 10

Skepticism

Answer 10

1950s 60s 70s skepticism around the legitimacy of receptors.

Question 11

Radioligand binding

Answer 11

Made commpounds radioactive, so when bind to ligands can measure radioactivity before and after etc.
Made rapid progress in understanding dynamic regulation of receptors.

Question 12

Ternary complex model

Answer 12

1980 - GPCR
When extracellular molecule binds to ligand, and G protein binds to intracellular part. Allosteric mechanism. Conformational change

Question 13

Finding GPCR as physical entities

Answer 13

By adding receptors to otherwise inactive system, system activated, showing evidence of gpcr efficacy and existence.

Question 14

Cloning GPCR

Answer 14

1986 - Back translating the base triplets allowed the gene to be derived. New receptor had 7 transmembrane sections, very similar to rhodhopsin.

Question 15

After Gene sequence found

Answer 15

Experiments done to find where and how ligands and g proteins bind to receptor.
Section on top of transmembrane space found to bind to ligand, G protein binds below.

Question 16

3D structure of GPCR

Answer 16

When ligand binds, conformational change in protein opens ‘cavity’ in which G protein can fit.
Kobilka’s crystal structure confirmed this to be true.

Question 17

GPCR desensitisation

Answer 17

After G protein binds to receptor, another protein phosphorylates receptor, it gets bound into vesicle and re integrated into membrane later.