Premium
Actions of acetylcholine and GABA on spontaneous contractions of the filariid, Dipetalonema viteae
Author(s) -
Christ Daryl,
Goebel Michael,
Saz Howard J.
Publication year - 1990
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1990.tb14190.x
Subject(s) - picrotoxin , acetylcholine , muscarine , chemistry , hexamethonium , gaba receptor antagonist , muscimol , bicuculline , muscarinic acetylcholine receptor , gabaa receptor , atropine , pharmacology , endocrinology , biochemistry , biology , receptor
1 Isotonic contractions were recorded from the filarial nematode, Dipetalonema viteae ( Acanthocheilonema viteae ), in an isolated tissue chamber. 2 Nicotine (10 −6 m ) and pilocarpine (10 −5 m ) increased the spontaneous contractions in the intact filariid, but acetylcholine (ACh, 10 −4 m ) and muscarine (10 −5 m ) were inactive. 3 When ACh was applied to an opened D. viteae , it was 10,000 times more potent. This indicates that the cuticle is an effective barrier to the penetration of ACh to the muscle cells. 4 The effects of ACh on the opened D. viteae were not affected by hexamethonium (10 −3 m ) or atropine (10 −5 m ) and were only partially reduced by (+)‐tubocurarine (10 −4 m ). 5 γ‐Aminobutyric acid (GABA, 10 −3 m ) reduced the spontaneous activity of the intact D. viteae; however, the effect of GABA had a slow onset and recovery. Muscimol (10 −5 m ) was more potent than GABA and had a more rapid onset and recovery. 6 GABA was 1,000 times more potent on the opened D. viteae than on the intact D. viteae . Baclofen (10 −3 m ) was inactive on both preparations. 7 The effect of GABA was not antagonized by bicuculline (10 −4 m ), picrotoxin (10 −5 m ) or penicillin G (10 −3 m ). 8 It is concluded that the filariid cuticle acts like a lipid structure and blocks the penetration of polar substances, such as ACh and GABA. Also, due to the lack of efficacy of the ACh and GABA antagonists, it was concluded that the nematode receptors are somewhat different from the mammalian ACh and GABA receptors.