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THE EFFECT OF HARMINE ON THE ACTION POTENTIAL OF THE GUINEA‐PIG ATRIAL MUSCLE DEPENDS ON THE EXTERNAL CALCIUM CONCENTRATION
Author(s) -
CARPENTIER ROBERT G.
Publication year - 1981
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.1476-5381.1981.tb09986.x
Subject(s) - harmine , calcium , chemistry , depressant , guinea pig , biophysics , pharmacology , endocrinology , biology , organic chemistry
1 The influence of the external calcium concentration on the effect of harmine 2 × 10 −5 M upon the guinea‐pig atrial muscle was analysed. Transmembrane potentials of contractile fibres were measured during exposure to the drug at 30°C 2 In preparations superfused with 1.35 mM Ca 2+ ‐Tyrode solution and driven at 60/min (1Hz) harmine depressed the amplitude of the action potential (AP) and the maximum velocity of the upstroke (d V /d t ). The resting potential was not affected. Harmine depressed similarly the d V /d t of fibres superfused with 2.7 mM Ca 2+ ‐Tyrode solution but the AP was slightly enhanced 3 Harmine diminished both the AP and the d V /d t of fibres superfused with 2.7 mM Ca 2+ ‐Tyrode solution and driven at a fast rate (180/min, 3 Hz). Increased external calcium concentration (5.4 mM) annulled the depressant effect on AP while the action on d V /d t persisted 4 It is concluded that the effect of harmine on the AP depends on the external calcium concentration. Increase [Ca 2+ ] o reverses the depressant effect of harmine because it annuls the effect of the drug on the slow component of the upstroke. The action on the initial fast component of the rising phase of the action potential persists.