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Antagonism of kinin effects on epithelia by Hoe 140: apparently competitive and non‐competitive interactions
Author(s) -
Cuthbert A.W.,
MacVinish L.J.,
Pickles R.J.
Publication year - 1992
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.1476-5381.1992.tb14526.x
Subject(s) - mepyramine , antagonist , competitive antagonist , antagonism , histamine , intracellular , chemistry , medicine , endocrinology , receptor antagonist , pharmacology , biology , receptor , biochemistry
1 Hoe‐140, a potent kinin receptor antagonist, was investigated for its ability to inhibit the effects of lysylbradykinin (kallidin) on a cultured colonic epithelium, HCA‐7 Colony 29, derived from a human adenocarcinoma. 2 Measurements of electrogenic chloride secretion (as short circuit current), and of intracellular Ca 2+ (from Fura‐2 fluorescence) were used to assess the action of lysylbradykinin in the absence and presence of Hoe 140. 3 From short circuit current data, Hoe 140 appeared to be a competitive antagonist with a K i value of 5 n m . However, with measurements of intracellular Ca 2+ Hoe 140 was apparently a non‐competitive antagonist with a K i of between 4–6 n m . 4 Because of the unexpected finding of non‐competitive antagonism, measurements were made with a second antagonist pair, histamine and mepyramine. Mepyramine behaved as a competitive antagonist against responses to histamine with a K i value of ≅5 n m when short circuit current measurements were evaluated. However, when intracellular Ca 2+ concentration was used as a measure mepyramine, 30 n m , produced a near parallel shift in the response curve, but at 100 n m the maximal response was depressed. 5 The reasons why the apparent type of antagonism depends upon the method of measurement is discussed, bearing in mind that the increase in intracellular Ca 2+ is a signal which precedes the increase in short circuit current.