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Some effects of nifedipine in guinea‐pig isolated trachealis
Author(s) -
Ahmed F.,
Foster R.W.,
Small R.C.
Publication year - 1985
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.1476-5381.1985.tb17380.x
Subject(s) - nifedipine , trachealis muscle , chemistry , tetraethylammonium , acetylcholine , histamine , medicine , endocrinology , pharmacology , potassium , calcium , membrane potential , biochemistry , organic chemistry , charybdotoxin
1 In trachealis depolarized by a K + ‐rich medium, nifedipine (0.001–1 μmol 1 −1 ) caused concentration‐dependent antagonism of CaCl 2 ‐induced increase in tension, moving the CaCl 2 log concentration‐effect curve to the right and depressing the maximal response. 2 In trachealis in normal Krebs solution, similar concentrations of nifedipine had marked antispasmogenic activity against the responses to potassium chloride (KCl) and tetraethylammonium (TEA). However, nifedipine had little, if any, antispasmogenic activity against the responses to acetylcholine or histamine. 3 Nifedipine 1 μmol 1 −1 was tested for spasmolytic activity in tissues generating tension in response to the EC 50 of acetylcholine, KCl or CaCl 2 . In producing spasmolysis nifedipine was most effective against CaCl 2 and least effective against acetylcholine. 4 Nifedipine (0.01–1 μmol −1 ) had little or no effect on the tone of trachealis in normal Krebs solution. 5 Intracellular electrophysiological recording showed that nifedipine 1 μmol 1 −1 could abolish spontaneous slow wave activity. This was associated with very minor depolarization and little or no loss of mechanical tone. In tissues treated with TEA (8 mmol 1 −1 ) nifedipine abolished spike and slow wave discharge and reduced mechanical activity to the pre‐TEA level. 6 It is concluded that nifedipine prevents KCl‐ or TEA‐induced spasm by inhibition of Ca 2+ influx. Spasm evoked by acetylcholine or histamine and the maintenance of spontaneous tone depend largely on mechanisms for increasing the cytoplasmic concentration of free Ca 2+ which are resistant to nifedipine.