lacétylcholine

Lacétylcholine, commonly known as acetylcholine, is a neurotransmitter in both the peripheral and central nervous systems. It mediates fast synaptic transmission at the neuromuscular junction and modulates autonomic and central circuits. In the brain, acetylcholine influences arousal, attention, learning, and memory.

It is a quaternary ammonium ester formed from choline and acetic acid. In neurons it is synthesized by choline acetyltransferase (ChAT) from choline and acetyl-CoA, and is transported into synaptic vesicles by the vesicular acetylcholine transporter (VAChT). Upon Ca2+-dependent vesicle fusion, acetylcholine is released into the synaptic cleft. It is rapidly inactivated by enzymatic hydrolysis rather than reuptake.

Acetylcholine acts on two major receptor families: nicotinic acetylcholine receptors (nAChRs), which are ligand-gated ion channels, and muscarinic acetylcholine receptors (mAChRs), which are G protein-coupled receptors. Nicotinic receptors mediate fast excitation at the neuromuscular junction and in autonomic ganglia, while muscarinic receptors regulate heart rate, smooth muscle, and glandular secretion in peripheral tissues, as well as various CNS effects.

Termination of signaling occurs primarily through hydrolysis of acetylcholine by acetylcholinesterase in the synaptic cleft, yielding choline and acetate. Choline is transported back into the presynaptic terminal by a high-affinity choline transporter and reused to resynthesize acetylcholine. A small fraction is degraded by acetylcholinesterase without reuptake.

Clinical relevance includes disorders of cholinergic transmission such as myasthenia gravis and Alzheimer's disease. Acetylcholinesterase inhibitors increase acetylcholine levels to improve transmission in such conditions. Toxicity from organophosphates or nerve agents causes excessive cholinergic stimulation; management may involve supportive care and targeted agents depending on symptoms.