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Effects of tetrodotoxin on relaxation of pig duodenal circular muscle induced by C‐terminal fragments of cholecystokinin
Author(s) -
Kimura Ikuko,
Kondoh Takashi,
Kimura Masayasu
Publication year - 1989
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.1476-5381.1989.tb11876.x
Subject(s) - cholecystokinin , apamin , tetrodotoxin , tetraethylammonium , chemistry , stimulation , endocrinology , medicine , cholecystokinin receptor , proglumide , inhibitory postsynaptic potential , antagonist , relaxation (psychology) , depolarization , tetraethylammonium chloride , biophysics , potassium , potassium channel , receptor , biology , biochemistry , organic chemistry
1 The mechanisms by which cholecystokinin (CCK)‐C‐terminal peptides relax the isolated duodenal circular muscles of pigs were compared with mechanisms involving high potassium and electrical stimulation. 2 The relaxation (30%) induced by CCK‐8 0.263 n m was completely and non‐competitively blocked by tetrodotoxin (TTX) 0.313 μ m , and was enhanced 2–2.5 times by mesaconitine 0.158 μ m , tetraethylammonium (TEA) 0.597 m m and ouabain 0.136 μ m . 3 The TTX sensitivity was greater for CCK‐8 and CCK‐6, than for CCK‐5 and CCK‐4. 4 High potassium (11.8–23.6 m m )‐induced, or electrically stimulated (0.3–30 Hz) relaxation showed similar characteristics except that they were not antagonized by the CCK antagonist P3‐I (168 μ m ). 5 Apamin (0.385–3.85 μ m ) enhanced relaxation induced by 10.6 m m K + , but did not affect relaxation induced by CCK‐8. 6 These results indicate that: (1) CCK‐8, K + , and transmural electrical stimulation relax duodenal circular muscles by releasing an endogenous inhibitory substance; (2) the latter two do not mediate the release of CCK; and (3) the mechanisms for relaxation by CCK‐4 are different from those of CCK‐8.