Choline ester hydrolases in diaphragm muscle

An immunological study of rat acetylcholinesterase: comparison with acetylcholinesterases from other vertebrates

We have examined the immunoreactivity of acetylcholinesterase from different vertebrate species with a rabbit antiserum raised against the purified rat brain hydrophobic enzyme (G4 form). We found no significant interaction with enzymes from Electrophorus, Torpedo, chicken, and rabbit. The antiserum reacted with acetylcholinesterases from the brains of the other mammalian species studied, with titers decreasing in the following order: rat = mouse greater than human greater than bovine. The serum was inhibitory with murine and human acetylcholinesterases, but not with the bovine enzyme. The inhibition was partially depressed in the presence of salt (e.g., 1 M NaCl). In those species whose acetylcholinesterase was recognized by the antiserum, both soluble and detergent-soluble fractions behaved in essentially the same manner, interacting with the same antibodies. The apparent immunoprecipitation titer was decreased in the presence of salt, and it did not make any difference whether NaCl was included in the solubilization procedure or added to the extracts. Both G1 and G4 forms of acetylcholinesterase in the soluble and detergent-soluble fractions were recognized by the antiserum, and in the case of the human enzyme, by monoclonal antibodies produced against human erythrocyte acetylcholinesterase. However, the monomer G1 showed a clear tendency to form smaller complexes and precipitate less readily than the tetramer G4. Although we cannot exclude the existence of significant differences between the various molecular forms of acetylcholinesterase, our results are consistent with the hypothesis that they all derive from the same gene or set of genes by posttranslational modifications.

Demonstration of acetylcholinesterase by semipermeable membrane technique: estimation of soluble and fixation-labile portions in different regions of the central nervous system

A histochemical method for the demonstration of acetylcholinesterase using semipermeable membranes is described. This technique prevents any loss of enzyme activity caused by dissolution and/or fixation. The soluble and fixation-labile portions of acetylcholinesterase were estimated in several regions of the central nervous system of the rat and differences were found. The method improves the accuracy of the histochemical demonstration of the acetylcholinesterase on the light microscopical level.

Actions of the selective inhibitor of cholinesterase tetramonoisopropyl pyrophosphortetramide on the rat phrenic nerve-diaphragm preparation

1. Tetramonoisopropyl pyrophosphortetramide (iso-OMPA) added for 15 min to the rat isolated phrenic nerve-diaphragm in a concentration of 30 muM, produced a complete selective and stable inhibition of cholinesterase. A concentration of 3 muM produced near complete inhibition of cholinesterase, and a concentration of 300 muM also inhibited acetylcholinesterase marginally.2. Inhibition of cholinesterase was associated with a sustained increase in the neuromuscular blocking action of exogenous butyrylcholine but not of exogenous acetylcholine. Iso-OMPA, 300 muM, in addition caused transient increases in the sensitivity of the rat diaphragm to exogenous acetylcholine and butyrylcholine. In the same concentration, it had a curare-like action on the frog rectus abdominis muscle preparation.3. Iso-OMPA, 30 muM, caused reversible increases in the amplitude of the twitch response and tetanic responses, which were of a similar magnitude in the indirectly stimulated preparation and the directly stimulated curarized preparation. Caffeine had a similar effect on the twitch response and its effectiveness was increased by iso-OMPA, and vice-versa. Amongst anticholinesterases, octamethyl pyrophosphortetramide and tetraethylpyrophosphate also enhanced the amplitude of the tetanic response, but paraoxon, dyflos, and mipafox did not.4. It is concluded that iso-OMPA, in concentrations (3 and 30 muM) which in 15 min give near maximal or maximal selective inhibition of cholinesterase, has no effect on the transmission of nerve impulses at the neuromuscular junction, but enhances reversibly the amplitude of the contractile response to stimulation by a direct action upon the muscle fibre, which involves a mechanism related to but not identical with that by which caffeine potentiates twitch tension. In higher concentrations, iso-OMPA has a curare-like action at the neuromuscular junction.