Tacrine slows the rate of ageing of sarin-inhibited acetylcholinesterase.

Bovine erythrocyte acetylcholinesterase was inhibited by the organophosphate sarin, and the rate of ageing (the time-dependent decrease in the ability of an oxime to reactivate the enzyme) was studied. At pH 7.0 and 37 degrees C, 10(-5) M or 10(-6) M tacrine (tetrahydroaminoacridine) decreased the rate of ageing in low ionic strength buffer. Tacrine at 10(-5) M also significantly decreased the rate of ageing in 150 mM NaCl. The results indirectly demonstrated that the inhibition of substrate hydrolysis by tacrine is reversible, and that tacrine does not prevent reactivation of sarin-inhibited acetylcholinesterase. Both these observations, which were also made for rat brain acetylcholinesterase, are in contrast with reports in the literature.