Muscarinic receptor subtypes in lung. Clinical implications.

Several subtypes of muscarinic receptors have been identified in airways and lung parenchyma of different species, including humans. M1 receptors may be present in parasympathetic ganglia where they appear to facilitate ganglionic neurotransmission. M2 receptors seem to be located on cholinergic nerve endings where they function as "autoreceptors," inhibiting acetylcholine release. M3 receptors appear to be located on effector cells, smooth muscle, and mucus secreting glands. Experimental data in support of this view are presented and discrepant data are discussed.