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Mechanisms of intrinsic tone in bullfrog lung: relaxant effects of indomethacin, ouabain and potassium
Author(s) -
Downes Hall,
Edelstein Robert A.,
Taylor Stephen M.
Publication year - 1986
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.1476-5381.1986.tb10200.x
Subject(s) - ouabain , chemistry , isoprenaline , bullfrog , calcium , potassium , endocrinology , medicine , papaverine , contraction (grammar) , theophylline , stimulation , sodium , biophysics , biology , organic chemistry
1 Bullfrog hemilungs showed minimal relaxation (9 ± 2% of the maximal relaxant effect of theophylline, I max ) after a 16 h incubation in 10 −5 M indomethacin, indicating that prostaglandin synthesis plays little or no role in the high intrinsic tone characteristic of this preparation. 2 A higher concentration of indomethacin (10 −4 M) produced greater relaxation (23 ± 3% of I max ), but also markedly potentiated isoprenaline‐induced relaxation. The interaction with isoprenaline was similar to that previously found for papaverine, a phosphodiesterase inhibitor. 3 Ouabain (10 −5 and 10 −4 M) produced an initial contraction followed by marked relaxation (50% of I max ), indicating that a ouabain‐sensitive mechanism is of major importance in the maintenance of intrinsic tone. 4 Ouabain‐treated hemilungs showed (a) reversal (relaxation) of the normal contractile response to 26 mM potassium and (b) marked impairment of the contractile response to calcium in calcium‐depleted preparations. These effects suggest that ouabain‐induced relaxation reflects a drug action on calcium movements. 5 The marked relaxation (30 to 40% of I max ) produced by 26 mM potassium in ouabain‐treated hemilungs is of particular interest in that it indicates a mechanism of potassium‐induced relaxation distinct from stimulation of sodium‐potassium ATPase.