Subtypes of muscarinic receptors on adrenergic nerves and vascular smooth muscle of the canine saphenous vein

J Pharmacol Exp Ther. 1987 Apr;241(1):64-7.

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.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Acetylcholine / pharmacology
  • Adrenergic Fibers / metabolism*
  • Animals
  • Atropine / pharmacology
  • Dogs
  • Electric Stimulation
  • Gallamine Triethiodide / pharmacology
  • Mathematics
  • Muscle Contraction
  • Muscle, Smooth, Vascular / metabolism*
  • Pirenzepine / pharmacology
  • Receptors, Muscarinic / metabolism*
  • Saphenous Vein / metabolism

Substances

  • Receptors, Muscarinic
  • Pirenzepine
  • Atropine
  • Acetylcholine
  • Gallamine Triethiodide