Muscarinic receptor subtypes on rat pancreatic acini: secretion and binding studies

Am J Physiol. 1986 Aug;251(2 Pt 1):G275-9. doi: 10.1152/ajpgi.1986.251.2.G275.

Abstract

Characterization of muscarinic receptor subtypes on rat pancreatic acinar cells was examined by using specific muscarinic receptor antagonists to study amylase secretion and binding of [N-methyl-3H]scopolamine ([3H]NMS). Rat pancreatic acini were dispersed in HEPES-Ringer buffer and incubated with acetylcholine +/- 4-diphenylacetoxy-N-methylpiperadine-methiodide (4-DAMP, a specific M2 muscarinic receptor antagonist) or +/- pirenzepine (a specific M1 muscarinic receptor antagonist). 4-DAMP (10(-9) to 10(-6) M) caused a progressive parallel rightward shift in the acetylcholine dose-response curve without a change in maximal amylase release. Only high concentrations of pirenzepine (10(-6) to 10(-4) M) caused a rightward shift in the dose-response curve to acetylcholine. Schild analysis of the data indicated an inhibitory constant (Ki) of 200 pM for 4-DAMP and 183 nM for pirenzepine. The slope of the Schild regression lines was not different from unity, suggesting competitive inhibition. Binding of 50 pM [3H]NMS was specific, rapid, and saturable. [3H]NMS binding was displaced by increasing concentrations of 4-DAMP or pirenzepine with apparent Ki's of 102 pM and 330 nM, respectively, and similar maximal binding levels of 60 fmol/mg prot. We have demonstrated that 4-DAMP has an approximately 1,000-fold greater potency than pirenzepine to inhibit amylase release and binding, indicating that cholinergic-stimulated amylase release from pancreatic acini is mediated by M2 muscarinic receptors.

Publication types

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

MeSH terms

  • Acetylcholine / pharmacology
  • Amylases / metabolism*
  • Animals
  • Benzodiazepinones / pharmacology
  • Binding Sites
  • Male
  • N-Methylscopolamine
  • Pancreas / metabolism*
  • Piperidines / pharmacology
  • Pirenzepine
  • Rats
  • Rats, Inbred Strains
  • Receptors, Muscarinic / drug effects
  • Receptors, Muscarinic / isolation & purification
  • Receptors, Muscarinic / metabolism*
  • Scopolamine Derivatives / metabolism
  • Tritium

Substances

  • Benzodiazepinones
  • Piperidines
  • Receptors, Muscarinic
  • Scopolamine Derivatives
  • Tritium
  • Pirenzepine
  • 4-diphenylacetoxy-1,1-dimethylpiperidinium
  • Amylases
  • Acetylcholine
  • N-Methylscopolamine