On muscarinic control of neurogenic mucus secretion in ferret trachea.

Abstract

1 Muscarinic receptor subtypes mediating neurogenic mucus secretion in ferret trachea were characterized in vitro and in vivo using 35sQ, as a label for secreted mucus, and the muscarinic receptor antagonists telenzepine for the M1 receptor subtype, methoctramine for the M2 subtype and 4-diphenylacetoxy-N-methylpiperidine methobromide (4-DAMP) for the M3 receptor. We also performed receptor binding and mapping studies. 2. Each muscarinic antagonist displaced [N-methyl-3H]scopolamine binding with high-affinity binding constant (KH) values of 1-9, 2-7 and 5 0 nm for telenzepine, methoctramine and 4-DAMP, respectively. Muscarinic M1 and M3 receptors localized to submucosal glands, whereas M2 receptors did not.3. In vitro, electrical stimulation (50 V, 10 Hz, 0 5 ms for 5 min) increased 35So4 output by 160%. Telenzepine did not inhibit the neurogenic secretory response at concentrations twoor twentyfold its KH value, nor did it inhibit secretion induced by acetylcholine (ACh). 4-DAMP inhibited neurogenic secretion by 80 and 95%, respectively, at concentrations twoand twentyfold its KH value, and also inhibited ACh-induced secretion. Methoctramine potentiated neurogenic secretion induced at 2-5 Hz (50 V, 0 5 ms for 5 min) in a dose-related (5-4-100 nM) manner with increases of 33-451 % above electrically stimulated values. Methoctramine did not potentiate secretion induced at 10 Hz and did not have any effect on ACh-induced secretion. 4. In vivo, vagal stimulation (10 V, 10 Hz, 2 ms for 8 min) increased output of 35S04 by -120%. Telenzepine had no significant effect on neurogenic secretion. Methoctramine approximately doubled the stimulated response, whereas 4-DAMP abolished the stimulated secretory response. 5. We conclude that in ferret trachea, cholinergic nerve stimulation increases mucus secretion via muscarinic M3 receptors on the submucosal glands. The magnitude of the secretory response is regulated by neuronal M2 muscarinic receptors. The muscarinic M1 receptors localized to the submucosal glands do not appear to be involved with mucus secretion.Cholinergic nerves are the dominant neural pathway involved in control of a number of airway functions, including mucus secretion (Rogers, 1996). Physiological responses to cholinergic nerve stimulation are mediated via cholinergic muscarinic receptors (Barnes, 1993). Four subtypes of muscarinic receptor (M1-M3, and possibly M4) can be demonstrated pharmacologically, although the muscarinic antagonist drugs currently available are not highly selective for the different receptor subtypes (Eglen, Reddy & Watson, 1994). In the airways, Ml receptors are localized to parasympathetic ganglia, submucosal glands and, in humans, to the alveolar walls (Barnes, 1993

Vagal Regulation of Respiratory Clocks in Mice

“…Thus, the increased nocturnal mucin secretion may be explained by an increase in muscarinic receptors in conjunction with an enhanced vagal tone at night. Because it has been demonstrated that cholinergic nerve stimulation promotes mucus secretion via Chrm3 receptors in the ferret trachea (Ramnarine et al, 1996), a circadian raise in Chrm3 receptor levels may trigger the enhanced mucus secretion during night time. The circadian change of the acetylcholine neurotransmission, as revealed in this study, extends our understanding of the pathophysiology of asthmatic symptoms and airway diseases, and may help to improve therapeutic strategies.…”

“…Because at present knowledge on circadian output genes is limited, we concentrated on physiological processes in the respiratory system that are known to display circadian characteristics. Because it is known that pharmacological agents relating to the muscarinic acetylcholine receptor have a strong effect on airway contraction and mucin secretion in respiratory system (Barnes, 1993), we started to examine the mRNA expression profiles of various subtypes of muscarinic receptor genes (Chrm1-4 ) that are known to be expressed in the lung (Barnes, 1993;Ramnarine et al, 1996). Although quantitative real-time PCR analysis did not show circadian variation in Chrm1 mRNA levels (one-way ANOVA; F (5,23) ϭ 1.040; p ϭ 0.4180), we noticed a significant circadian rhythm in Chrm2 expression (one-way ANOVA; F (5,24) ϭ 15.992; p Ͻ 0.0001), peaking at CT16 with a 2.63-fold amplitude (Fig.…”

Bronchodilating effect of combined therapy with ipratropium bromide and ondansetron in patients with COPD

“…Acetylcholine, released from the parasympathetic nerves, stimulates muscarinic receptors, causing bronchoconstriction and mucus secretion. The effect of acetylcholine in the airways is mediated mainly through three muscarinic receptor subtypes, designated M1, M2 and M3 (16). M1 receptors facilitate neurotransmission through the cholinergic ganglia; M2 receptors are found on pre and postganglionic parasympathetic nerves and inhibit release of acetylcholine, while M3 receptors are present in airway smooth muscle (ASM) and submucosal glands and are responsible for mediating bronchoconstriction and mucus secretion (16,17).…”

“…The effect of acetylcholine in the airways is mediated mainly through three muscarinic receptor subtypes, designated M1, M2 and M3 (16). M1 receptors facilitate neurotransmission through the cholinergic ganglia; M2 receptors are found on pre and postganglionic parasympathetic nerves and inhibit release of acetylcholine, while M3 receptors are present in airway smooth muscle (ASM) and submucosal glands and are responsible for mediating bronchoconstriction and mucus secretion (16,17). Inhibition of acetylcholine release by M2 receptors may be decreased or lost due to M2 receptor dysfunction in asthma and in COPD (18,19), resulting in unopposed activity at the M3 receptors.…”

Physiological Roles of Muscarinic Receptors

“…Of the five cloned muscarinic receptor subtypes, human lung expresses only three receptor subtypes (Ml' M2 and M 3 ), which are differentially distributed in the airways (Mak et al 1992;Barnes, 1993;Haddad et al 1994;Ramnarine et al 1996). M 1 -receptors are found in parasympathetic ganglia where they facilitate neurotransmission, and on alveolar walls where their function remains unclear.…”