atsetüülkoliini

Atsetüülkoliini, known in English as acetylcholine (ACh), is a neurotransmitter in the cholinergic system of many animals. It is a quaternary ammonium ester formed from choline and acetic acid and is typically encountered in the form of a salt, such as acetylcholine chloride, in physiological solutions.

Synthesis and release occur in cholinergic neurons. Choline acetyltransferase catalyzes the formation of atsetüülkoliini from acetyl-CoA and choline in the cytoplasm. It is stored in synaptic vesicles and released into the synaptic cleft upon depolarization and calcium influx. After release, it rapidly interacts with receptors on post-synaptic cells or is degraded to terminate signaling.

Atsetüülkoliini acts on two main receptor families: nicotinic receptors (ionotropic) and muscarinic receptors (metabotropic). Activation of nicotinic receptors at neuromuscular junctions leads to muscle contraction, while muscarinic receptor activation modulates various autonomic and central nervous system responses. In the central nervous system, acetylcholine is involved in attention, learning, memory, and arousal.

Termination of atsetüülkoliini signaling is accomplished mainly by acetylcholinesterase, which hydrolyzes it to choline and acetate. Choline is taken back up into the presynaptic neuron by the high-affinity choline transporter and reused for new neurotransmitter synthesis.

Clinical relevance includes its role in cognitive function and neuromuscular transmission. Alterations in cholinergic signaling are associated with diseases such as Alzheimer's disease, and acetylcholinesterase inhibitors can be used to mitigate some symptoms by increasing acetylcholine levels in synapses.