title: Subtypes of muscarinic receptors on adrenergic nerves and vascular smooth muscle of the canine saphenous vein.
abstract: Experiments were designed to characterize pre- and postjunctional muscarinic receptors in the canine saphenous vein. In rings contracted by 2-Hz electrical stimulation, acetylcholine produced concentration-dependent relaxations that result from prejunctional inhibition of norepinephrine release from adrenergic nerve endings (prejunctional effect). In quiescent preparations, acetylcholine caused concentration-dependent contractions (postjunctional effect). Both responses to acetylcholine were inhibited in a competitive manner by atropine, pirenzepine and gallamine. The affinity of atropine for pre- and postjunctional muscarinic receptors was similar (pKB = 8.7 and 9.2, respectively). However, gallamine displayed higher affinity for the prejunctional than for the postjunctional receptor (pKB = 6.1 and 4.7, respectively), whereas the converse was true for pirenzepine (pKB = 6.5 and 8.1). The data support the presence in the canine saphenous vein of two muscarinic receptor subtypes, M1 postjunctionally and M2 prejunctionally, which are distinguishable by selective antagonists.
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000320:Adrenergic Fibers / Q000378:metabolism*; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D004285:Dogs; D004558:Electric Stimulation; D005703:Gallamine Triethiodide / Q000494:pharmacology; D008433:Mathematics; D009119:Muscle Contraction; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D010890:Pirenzepine / Q000494:pharmacology; D011976:Receptors, Muscarinic / Q000378:metabolism*; D012501:Saphenous Vein / Q000378:metabolism
chemical_list: D011976:Receptors, Muscarinic; D010890:Pirenzepine; D001285:Atropine; D000109:Acetylcholine; D005703:Gallamine Triethiodide