Receptors for neurotransmitters in opossum oesophagus muscularis mucosa

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Abstract
1 Muscularis mucosa of the distal oesophagus of the opossum contains nerves which release acetylcholine and substance P(SP)-like material on field stimulation. The release of SP-like material appeared to be inhibited by the presence of exogenous muscarinic agonists and potentiated by muscarinic antagonists. Analysis of the postjunctional receptors involved using carbachol, McNeil A-343 (McN A-343), atropine and pirenzipine suggested that the receptors were not typical M2-muscarinic receptors. The potency of agonists and antagonists were consistent with some receptor properties resembling M1-muscarinic receptors. 2 Prejunctional receptors to opiates, adenosine, agonists at α2-adrenoceptors and prostaglandins were not detected. 3 Receptors for tachykinins were present on the muscle in this tissue, but did not resemble clearly either SP-E or SP-P type receptors. They appear to be undifferentiated since most tachykinins were of similar potency. 4 These results suggest that not all postjunctional muscarinic receptors in intestinal smooth muscle are M2 in type. There may be a gradation of types between M1 and M2.