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Effects of calcium and nifedipine on noradrenaline- and PGF-2-induced activity of the ampullary–isthmic junction of the human oviduct in vitro

Summary. From 22 women undergoing hysterectomy at various stages of the menstrual cycle, strip preparations were dissected from the outer, longitudinal and the inner, circular smooth muscle layers of the ampullary–isthmic junction (AIJ). The strips were mounted in organ baths, and isometric tension was recorded. Spontaneous contractions were recorded mainly in circular muscle strips. Contractions were elicited by 127 mM-K⁺, 10^–6 M-noradrenaline and 10^–6 M-PGF-2. Potassium induced biphasic responses that were slightly different in the two tissues. In circular muscle strips, noradrenaline and PGF-2 induced phasic contractions superimposed on a rise in tone. In longitudinal muscle specimens, the two compounds produced tonic responses. All types of mechanical activity were inhibited by removal of extracellular calcium. K⁺-induced responses and phasic contractions produced by noradrenaline and PGF-2 could be abolished by 10^–6 M-nifedipine whereas the tonic contractions in the circular and longitudinal muscle were more resistant to the calcium antagonist. The results suggest that K⁺-induced responses in circular and longitudinal muscle of the human AIJ, and the phasic contractions in circular muscle, depend on calcium influx via potentialsensitive membrane channels. Receptor-operated calcium channels seem to be involved in the tonic contractions observed mainly in the longitudinal smooth muscle.