Comparison of the effects of eserine and neostigmine on the leech muscle preparation.

The relative potencies of eserine and neostigmine were determined on three preparations of cholinesterase. Eserine was found to be twice as potent as neostigmine on the pseudocholinesterase of horse plasma, half as potent on the true cholinesterase of cat central nervous system, but twelve times as potent on the true cholinesterase prepared from the leech body wall. On the leech preparation, about ten times smaller concentrations of eserine than of neostigmine were required to potentiate the acetylcholine response, but after removal of the anticholinesterase from the bath fluid, the potentiation persisted much longer after neostigmine than after eserine. The greater sensitivity of the leech muscle to eserine is fully accounted for by the fact that its cholinesterase is more sensitive to eserine than to neostigmine. The longer lasting potentiation after neostigmine on the other hand suggests that this anticholinesterase becomes more firmly attached to the cholinesterase receptors in this muscle than does eserine.