**6. Muscarinic receptors in avian trachea**

Another study characterized a muscarinic receptor in chicken trachea controlling secretion of chlorides. In the study the chicken trachea was stimulated to secrete chloride ions by the application of acetyl choline and this was completely inhibited by bumetanide suggesting the presence of a functional muscarinic receptor in the avian trachea. In the study they classified the receptor subtype as M4, which probably is involved in ion transport on exocrine glands and mucosal cells [31].
