Acetylcholine receptor antagonists in acute respiratory distress syndrome: much more than muscle relaxants

Table 1 Types of AChR with their locations and main function

Type	Location of expression	Function
nAChR
Muscle-type	Neuromuscular junction	Muscle contraction, mainly by increased Na⁺ and K⁺ permeability
Neuronal-type	Autonomic ganglia	Activation of autonomic nervous system (sympathetic and parasympathetic), mainly by increased Na⁺and K⁺ permeability
	Hippocampus / cortex	Cognition, modulate the induction of synaptic plasticity, effect on learning and memory formation, i.e., can improve neurovascular coupling
	Midbrain	Reward center and initiation of the nicotine addiction process
	Neuro-endocrineneurons in the hypothalamus	Facilitate the Ca²⁺-dependent release of vasopressin and oxytocin
	Others	Improvement of neurovascular coupling (in neurodegenerative disease and ischemia)
mAChR
M1	Autonomic ganglia	Mediates slow EPSP in postganglionic nerve
	Exocrine glands	Stimulates secretion
	Central nervous system	Activates slow after-depolarizing potentials in neurons
M2	Heart	Reduce of heart rate, contractile forces of the atrium and conduction velocity in AV node
M2	Central nervous system	Activates slow after-depolarizing potentials in neurons
M3	Smooth muscles	Vasoconstriction, vasodilatation, bronchoconstriction
	Endocrine and exocrine glands	Stimulate secretion
	Central nervous system	Activates slow after-depolarizing potentials in neurons
	Eye	Lacrimation, miosis and accommodation by contraction of the sphincter papillae and ciliary body
M4	Central nervous system	Activates slow after-depolarizing potentials in neurons
M5	Not well known	-