The role of butyrylcholinesterase (BuChE) and acetylcholinesterase (AChE) in regulating acetylcholine (ACh) lifetime was investigated by use of selective cholinesterase (ChE) inhibitors. Addition of 1 μM tetraisopropylpyrophosphoramide (iso-OMPA) led to a 98% inhibition of BuChE activity with little or no effect on AChE activity. This inhibition wa accompanied by a 26% increase in the amplitude and a 43% prolongation in the half-relaxation time of contractions elicited by electric field stimulation (EFS). Coapplication of BW 284C51 (a selective AChE inhibitor) and 1 μM iso-OMPA resulted in increases of 2-fold in the amplitude and 10-fold in the half-relaxation time of EFS-induced contractions. These alterations were accompanied by small but sustained baseline contractures that were antagonized completely by incubation with exogenous BuChE (2.5 80300-8/asset/equation/feb20014579390803008-math-si1.gif?v=1&s=e71fb3f1e1fe2df6a72030be3e8a337b3a3611a7)
). The results suggest that BuChE serves to coregulate the lifetime of ACh in canine tracheal smooth muscle.
