Pre-junctional muscarinic autoreceptors in bovine airways.
We searched for pre-junctional inhibitory muscarinic receptors in isolated bovine trachealis strips and bronchial rings. Electric stimulation (ES)-induced tritiated acetylcholine ([(3)H]-ACh)-release and isometric contractions were determined in muscles incubated with the non-selective muscarinic agonist pilocarpine, the non-selective muscarinic antagonist atropine, the selective M(2)-receptor antagonists methoctramine and gallamine, or the selective M(4)-receptor antagonist PD102807. Electric field stimulation (EFS)-induced isometric contractile responses were assessed in trachealis strips and bronchial rings treated with 10(-9)-10(-5)M methoctramine, gallamine or PD102807. Pilocarpine (10(-6) and 10(-5)M) and atropine (10(-7)M) significantly decreased and increased ES-evoked [(3)H]-ACh-release, respectively. The enhancing effect of atropine on [(3)H]-ACh-release prevailed over the inhibitory effect of pilocarpine. M(2)- and M(4)-receptor antagonists did not increase EFS-induced contraction or ES-induced [(3)H]-ACh-release. However, 10(-7)M methoctramine, gallamine or PD102807 significantly attenuated the inhibitory effects of pilocarpine 10(-5)M on ES-induced [(3)H]-ACh-release.


CONCLUSIONS
Muscarinic autoregulation is present in bovine airways but is not fully accounted for by M(2)- and M(4)-receptor subtypes.
Dipartimento di Medicina Interna e Specialità Mediche, Università di Genova, 16132 Genova, Italy.
Michele
M
Baroffio
Emanuele
E
Crimi
Lorenzo
L
Brichetto
Lucia
L
Zappi
Kai
K
Rehder
Vito
V
Brusasco
D000818:Animals; D017660:Autoreceptors / Q000096:biosynthesis* / Q000187:drug effects; D001980:Bronchi / Q000187:drug effects / Q000378:metabolism*; D002417:Cattle; D004558:Electric Stimulation; D018721:Muscarinic Agonists / Q000494:pharmacology; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism; D011976:Receptors, Muscarinic / Q000096:biosynthesis*; D014132:Trachea / Q000187:drug effects / Q000378:metabolism*
D017660:Autoreceptors; D018721:Muscarinic Agonists; D018727:Muscarinic Antagonists; D011976:Receptors, Muscarinic