Characteristics of action potentials and contractions evoked by electrical-field stimulation of pregnant human myometrium.

Evoked electrical and mechanical activities of pregnant human myometrium were recorded by the single sucrose-gap method. Each muscle strip has an individual rhythm of membrane excitability and the evoked activity was affected by spontaneous membrane fluctuation. However, high-frequency stimulation caused changes in the rhythm of fluctuation and the pattern of action potential converted from plateau to spike type. Twitch contractions evoked by spike potentials were summated and became fused tetanus in accordance with shortening of the pulse interval. This method is suitable for clarifying the excitation-contraction relationship in human myometrium.