The pharmacological profile of the competitive muscarinic antagonist (
2S, 3'R) 3-quinuclidinyl tropate, abbreviated (-)-2a, was evaluated on
rabbit vas deferens (M-1/M-4-like; pA(2)=9.10), guinea-pig left atriu
m (M-2; pA(2)=9.30), guinea-pig ileum (M-3; pA(2)=10.33) and guinea-pi
g uterus (M-4 putative; pA(2)=9.70) muscarinic receptors and on the fi
ve subtypes of muscarinic receptors expressed individually in CHO-K1 c
ells. The drug shows an affinity for the M-3 receptor subtype at least
10-fold higher than 4-DAMP, p-HHSiD and zamifenacin, used as referenc
e drugs. These results suggest (-)-2a as a novel, potent and selective
M-3 antagonist that may have therapeutic potential in the treatment o
f conditions associated with increased smooth muscle contractility.