Host-parasite relationships in echinococcosis—IV. Acetylcholinesterase and permeability regulation in the hydatid cyst wall

Abstract

1. (1) A specific acetylcholinesterase is present in homogenates of hydatid scolices and brood capsules of Echinococcus granulosus. The rate of hydrolysis of acetylcholine is 45 times that of butyrycholine. Enzyme activity is partially inhibited by physostigmine and hexaethyltetraphosphate (HETP). 2. (2) The reducing substance (“glucose”) contents of fluids of 22 hydatid cysts of the bovine lung ranged from 9·2–102·5 mg per cent, of 24 cysts of the bovine liver, from 13·9–101·1 mg per cent. The cyst fluid “glucose” level is higher in cysts from sheep than in cysts from cattle. 3. (3)In hydatid daughter cysts suspended in isotonic Krebs-Ringer's solution for 4 hr, the outward passage of “glucose” occurs very slowly. Passage is accelerated by the addition of small amounts of certain acetylcholinesterase inhibitors to the suspending solution and markedly by the addition of both HETP and either choline or acetylcholine. 4. (4) Accelerated outward passage of “glucose” also occurs when daugther cysts are suspended in hypotonic salt solutions of 0.04 M concentration or less. 5. (5) The weight changes of hydatid daughter cysts suspended in a variety of salt solutions of from 0·039 M to 0·616 M for 2·5 hr are slow, regular and predictable. In solutions similar chemically but more hypotonic, permeability control in the cyst wall appears to break down following a period of water imbibition at the expected rate. Acetylcholine chloride (0·01 M) maintains permeability control to a greater degree than does NaCl at the same molar concentration. 6. (6) Hydatid daughter cysts lose weight more rapidly when suspended in a hypertonic glucose-saline solution for 3 hr than they do in the same glucose-saline which contains small amounts of acetylcholinesterase inhibitors. 7. (7) Extracts of hydatid cyst fluid and hydatid tissues contian one or more unidentified quaternary ammonium compounds.