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Maintained contractions of rat uterine smooth muscle incubated in a Ca 2+ ‐free solution
Author(s) -
Mironneau C.,
Mironneau J.,
Savineau J.P.
Publication year - 1984
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.1476-5381.1984.tb10813.x
Subject(s) - muscle contraction , smooth muscle , uterus , chemistry , endocrinology , calcium , medicine , biophysics , anatomy , biology
1 The effects of acetylcholine (10 −4 m ), prostaglandin E 2 (10 −6 m ), vanadate (5 × 10 −4 m ) and fluoride (10 −2 m ) have been studied on the mechanical and electrical activities of rat myometrial strips perfused in Ca 2+ ‐free EGTA‐containing solutions. 2 All four substances produced maintained contractions which could be initiated repeatedly after exposure to Ca 2+ ‐free solution for more than 1 h, without a significant decrease. The largest contractions were obtained with vanadate and the smallest ones with acetylcholine. The tension was usually 7–30% of the control contraction triggered by an action potential in Ca 2+ containing solution. 3 Maintained contractions induced by fluoride were unaffected by isoprenaline while those induced by acetylcholine, prostaglandin E 2 and vanadate were completely relaxed. 4 Prostaglandin E 2 ‐and vanadate‐induced contractions were slightly reduced by Na + removal or by adding Ca 2+ antagonists. In contrast, contractions induced by acetylcholine were suppressed in Na + ‐free solution and largely inhibited in the presence of Ca 2+ antagonists. 5 The depolarization induced by acetylcholine in Ca 2+ ‐free solution was strongly dependent on the external Na + concentration. The relationship between the size of the acetylcholine‐induced depolarization and the membrane potential (shifted by constant currents) was linear, giving an apparent reversal potential for acetylcholine close to zero potential. 6 In Ca‐free solutions and in the presence of atropine, Na + action potentials of long duration can be evoked which produced contractions of the same order of magnitude as those initiated by acetylcholine‐induced depolarizations. 7 These results are consistent with the hypothesis that the maintained contractions in Ca 2+ ‐free solutions induced by several stimulants could be related to Ca 2+ ‐independent mechanisms (fluoride) or Ca 2+ release from an intracellular store. This latter mechanism would include both pharmacomechanical (prostaglandin E 2 , vanadate) and electromechanical (acetylcholine) coupling.