Dorje_1991_Eur.J.Pharmacol_203_417

The M1 potency (decrease in neurogenic response) of carbachol, oxotremorine, muscarine, arecaidine propargly ester (APE) and 4-(4-chlorophenylcarbamoyloxy)-2-butynyltrimethylammonium iodide (4-Cl-McN-A-343) in rabbit field-stimulated vas deferens (prostatic segments) increased up to 15-fold when calcium was lowered (3.5-1.0 nM). The M2 receptor-mediated increase in twitch height in response to carbachol and the M1 affinity of pirenzepine were independent of calcium concentration (2.5 and 1.0 mM). Thus, prostatic segments of rabbit vas deferens can be used successfully at 1.0 mM calcium to determine M1 potencies of agonists and M1 affinities of antagonists without counteracting stimulation of M2 receptors.