Muscarinic receptors in rat nasal mucosa are predominantly of the low affinity agonist type.

Abstract Specific [ 3 H]l-quinuclidinyl benzilate binding to rat nasal mucosa homogenates occurs to a homogeneous class of binding sites with K d = 60 ± 2 10 −12 M and B max = 8.1 ± 2 pmol/g tissue. Binding is stereoselectively inhibited by benzetimide enantiomers. Pirenzepine inhibits [ 3 H]l-quinuclidinyl benzilate binding with low affinity ( K i = 5.0 10 −7 M), classifying the binding sites as muscarinic M 2 -receptors. Methylfurtrethonium and methacholine inhibit [ 3 H]l-quinuclidinyl benzilate binding following an almost sigmoid curve at high concentrations pointing to the presence of mainly low affinity agonist binding sites.