Ac. Myers et Bj. Undem, MUSCARINIC RECEPTOR REGULATION OF SYNAPTIC TRANSMISSION IN AIRWAY PARASYMPATHETIC GANGLIA, American journal of physiology. Lung cellular and molecular physiology, 14(4), 1996, pp. 630-636
Muscarinic receptor regulation of synaptic transmission in guinea pig
bronchial parasympathetic ganglia was evaluated with the use of intrac
ellular recording of the intrinsic ganglion neurons. Methacholine (1 m
u M) decreased the amplitude of vagus nerve-stimulated fast excitatory
postsynaptic potentials (fEPSP) by 33 and 46% (at 0.8 and 8.0 Hz, res
pectively) but had no effect on the amplitude of the depolarizations e
voked by a bath-applied nicotinic receptor agonist. Methoctramine (1 m
u M) inhibited methacholine's effect on fEPSP but alone did not influe
nce the magnitude of the fEPSP evoked by vagus nerve stimulation. Meth
acholine (10 mu M) depolarized a subpopulation of neurons (similar to
4 mV), which was blocked by pirenzepine (0.1 mu M). In other neurons,
either no effect or a small (1-5 mV) hyperpolarization was noted. Chol
inergic contractions of bronchial smooth muscle elicited by electrical
field stimulation were potentiated by methoctramine to the same exten
t as those evoked by vagus nerve (preganglionic) stimulation. The data
indicate that M(2) receptor activation can lead to inhibition of pres
ynaptic acetylcholine release and consequently a significant inhibitio
n of synaptic transmission in bronchial parasympathetic ganglia. The p
hysiological role of this neuromodulatory effect appears limited, howe
ver, when studied in the in vitro setting.