Biosynthesis and Signaling of Acetylcholine and Adrenaline

Acetylcholine

Neurotransmitter synthesized from choline and acetylCoA.

how are levels of noradrenaline reduced

• transporters uptake 2 and net

• take noradrenaline into the presynaptic neuron or surrounding cells

• monoamine oxidase and COMT can metabolise the noradrenaline

Choline Acetyltransferase

Enzyme that synthesizes acetylcholine in neurons.

how is acetylcholine synthesised

• choline and acetylCoA

• choline acetyltransferase

Cholinergic Signaling

Fast synaptic transmission using acetylcholine.

Acetylcholinesterase

Enzyme that degrades acetylcholine in synapses.

key features of acetylcholine

• permanently positively charged nitrogen

  • key for binding to receptors

• ester group

  • links choline to the acetyl group

Ester Group in acetylcholine

Chemical group linking choline to acetyl in acetylcholine.

structure of acetylcholine

chromaffin cells

• found in adrenal medulla and sympathetic ganglia

• produce and secrete adrenaline and noradrenaline

Permanently Positively Charged Nitrogen

• found in acetylcholine

• important for binding to receptors

Tyrosine Hydroxylase

Enzyme converting tyrosine to L-DOPA.

DOPA Decarboxylase

Enzyme converting L-DOPA to dopamine.

Dopamine Beta-Hydroxylase

Enzyme converting dopamine to noradrenaline.

Phenyl Ethanolamine N-Methyltransferase

Enzyme converting noradrenaline to adrenaline.

VMAT

Vesicular transporter packaging and releasing monoamines.

Adrenoreceptors

G protein-coupled receptors for adrenergic signaling.

Alpha1 Adrenoreceptor

• Coupled with Gq

• relevant to cardiovascular disorders.

• responsible for vasoconstriction

• found on vascular smooth muscle

Alpha2 Adrenoreceptor

Linked to Gi, involved in inhibitory signaling.

Beta1 Adrenoreceptor

Linked to Gs, stimulates cardiac function.

NET

Transporter for noradrenaline reuptake into neurons.

Monoamine Oxidase

Enzyme metabolizing noradrenaline in surrounding cells.

Catechol-O-Methyltransferase (COMT)

Enzyme metabolizing catecholamines like noradrenaline.

Fast Synaptic Transmission

Rapid communication between neurons via neurotransmitters.

adrenergic transmission

• tyrosine enters by the aromatic amino acid transporter AAAT

• dopamine packaged into vesicles by transporter cells called vesicular monoamine transporter (VMAT)

• VMAT then releases adrenaline and binds to adrenoreceptor

adrenoreceptors vs nicotinic acetylcholine receptors

slower

adrenaline to noradrenaline secretion ratio

4:1

what enzyme converts noradrenaline into adrenaline in the adrenal medulla

• phenylethanolamine-N-methyltransferase