PMID- 17180451 OWN - NLM STAT- MEDLINE DCOM- 20071002 LR - 20181113 IS - 0165-7380 (Print) IS - 0165-7380 (Linking) VI - 31 IP - 2 DP - 2007 Feb TI - Segment-dependent expression of muscarinic acetylcholine receptors and G-protein coupling in the equine respiratory tract. PG - 207-26 AB - Muscarinic receptors are considered to be of comparable clinical importance in chronic obstructive pulmonary disease (COPD) in equines and in humans. At present, data are scarce on the expression and distribution of probable subtypes of these receptors and their signalling pathways in airway segments, including lung parenchyma and bronchial and tracheal epithelium with the underlying smooth muscle in horses. Specific [N-methyl-3H]scopolamine chloride ([3H]NMS) binding to all three tissues was saturable and of high affinity, with KD values ranging between 1.6+/-0.7 and 1.9+/-0.3 nmol/L. [3H]NMS binding identified a higher density of total muscarinic receptors (fmol/mg protein) in the trachea (720+/-59 nmol/L) than in bronchi (438+/-48 nmol/L) or lung (22 +/- 3 nmol/L). Competitive binding studies using [3H]NMS and the unlabelled subtype-selective antagonists pirenzepine and telenzepine (M1), methoctramine and himbacine (M2), 4-diphenylacetoxy-N-methylpiperidine (4-DAMP) (M3), tropicamide (M4) and mamba toxin (MT-3) (M4) indicated the presence of at least three muscarinic receptor subtypes in peripheral lung tissue (50:40:24-28%: M2>M3>M1), whereas in bronchus and trachea M2 subtypes (87-90%) predominated over M3 (14-22%), and M1 subtypes were lacking. No differences were found between tissues in high-affinity binding sites for carbachol in the absence (31-36%) or presence of guanosine 5'-triphosphate (GTP) (approximately 100%). Western blotting for G-protein alpha-subunits showed a much more robust expression of G(alphai1/2) in the trachea (with highest receptor density) than in the lung or bronchi, whereas G(alphas)-protein was dominantly expressed in bronchus. Concomitantly, carbachol inhibited isoproterenol- and GTP-stimulated adenylyl cyclase activity with increasing muscarinic receptor expression (trachea > bronchi > lung). We conclude that the expression and signalling pathways of muscarinic receptors in the equine respiratory tract are segment-dependent. These receptors might contribute to the pathogenesis of COPD in the horse and could provide potential drug targets for the therapeutic use of anticholinergics in this species. FAU - Abraham, G AU - Abraham G AD - Institute of Pharmacology, Pharmacy and Toxicology, Leipzig University, Leipzig. FAU - Kottke, C AU - Kottke C FAU - Ammer, H AU - Ammer H FAU - Dhein, S AU - Dhein S FAU - Ungemach, F R AU - Ungemach FR LA - eng PT - Journal Article PT - Research Support, Non-U.S. Gov't DEP - 20061215 PL - Switzerland TA - Vet Res Commun JT - Veterinary research communications JID - 8100520 RN - 0 (Muscarinic Agonists) RN - 0 (Muscarinic Antagonists) RN - 0 (Receptors, Muscarinic) RN - EC 3.6.1.- (GTP-Binding Proteins) RN - EC 4.6.1.1 (Adenylyl Cyclases) RN - VDR09VTQ8U (N-Methylscopolamine) SB - IM MH - Adenylyl Cyclases/metabolism MH - Animals MH - Binding, Competitive MH - Blotting, Western/veterinary MH - GTP-Binding Proteins/*metabolism MH - Horse Diseases/drug therapy/*metabolism MH - Horses MH - In Vitro Techniques MH - Muscarinic Agonists/pharmacology MH - Muscarinic Antagonists/pharmacology MH - N-Methylscopolamine/antagonists & inhibitors/*pharmacokinetics MH - Pulmonary Disease, Chronic Obstructive/drug therapy/metabolism/*veterinary MH - Receptors, Muscarinic/biosynthesis/drug effects/*metabolism MH - Respiratory System/drug effects/metabolism EDAT- 2006/12/21 09:00 MHDA- 2007/10/03 09:00 CRDT- 2006/12/21 09:00 PHST- 2005/08/12 00:00 [accepted] PHST- 2006/12/21 09:00 [pubmed] PHST- 2007/10/03 09:00 [medline] PHST- 2006/12/21 09:00 [entrez] AID - 10.1007/s11259-006-3396-z [doi] PST - ppublish SO - Vet Res Commun. 2007 Feb;31(2):207-26. doi: 10.1007/s11259-006-3396-z. Epub 2006 Dec 15.