Studies on the nicotinic acetylcholine receptor of human muscle.

Abstract

1.A radioimmunoassay was established for the measurement of anti-(acetylcholine receptor) antibodies in the serum of myasthenic patients. It was found that 87% of myasthenic serum samples contained elevated levels of circulating anti-(acetylcholine receptor) antibody but that there was no direct correlation between the antibody titre and disease severity. Also, the anti-(acetylcholine receptor) antibody titre was measured in a series of patients that underwent a course of plasma exchange. The antibody titre was found to decrease following plasma exchange and the majority of patients obtained complete clinical remission for periods of up to 18 months following the completion of exchanges. 2. The nicotinic acetylcholine receptor protein has been purified from human skeletal muscle by a procedure involving extraction in non-ionic detergent followed by affinity purification on immobilised a toxin. Purified receptor preparations had specific activities of 0.5-3.5mumol a bungarotoxin binding sites per gram protein and sedi-mented as a single 125I-alpha bungarotoxin-binding species in sucrose density gradient centrifugation with S20,w =9.5. The purified protein focussed as a single sharp band at pH 6.6 when labelled directly with 125I and at pH 5.1 when complexed to 125I-alpha bungarotoxin. Polyacrylamide gel electrophoresis under non-denaturing conditions of receptor-toxin complex showed a single protein component of similar mobility to that of acetylcholine receptor from Torpedo marmorata, whilst polyacrylamide gel electrophoresis of the purified receptor under denaturing conditions showed two major protein bands with molecular weights 42000 and 66000 respectively with the occasional appearance of minor components at 56000 and 85000. Only the 42000 subunit was labelled with the affinity reagent, [3H]-MBTA. The purified receptor bound 125I-alpha bungarotoxin and d-tubo-curarine with kD values of 0.5nM and 0.25muM respectively. It behaved similarly to impurified detergent-extracted human receptor in the radioimmunoassay for anti-(human acetylcholine receptor) antibodies and when injected into rabbits caused increased levels of the latter antibodies but did not cause experimental autoimmune myasthenia gravis.

Date of Award	1980
Original language	English
Awarding Institution	University of Bath