An Interaction Between the Electrical Activities of Longitudinal and Circular Smooth Muscles of Pregnant Mouse Uterus

Specific features of smooth muscle cells recorded from the placental region of the myometrium of pregnant rats

“…This uncoupled mechanical activity with the electrical activity is probably due to recording contractile response generated from the non-placental region. The membrane activity recorded from the circular muscle showed the spike with plateau potential as has been described by Osa (1974), and Osa & Kawarabayashi (1977). Fig.…”

“…However, treatment with oestradiol or oestradiol following pre-treatment with progesterone produced a spike with a plateau depolarization such as was observed from circular muscle cells during the middle stage of gestation. The plateau formation was also observed from circular muscles of the pregnant mouse myometrium (Osa, 1974;Osa & Kawarabayashi, 1977;Suzuki & Kuriyama, 1975b). However, the shape of spikes generated from the muscle cells of the placental region differed from those in animals treated with either oestradiol, progesterone or both.…”

“…Furthermore, the propagation of contraction recorded by the cinematographic method showed a distinct delay in the placental region as compared to the nonplacental region (Kuriyama & Csapo, 1961). Osa (1974) and Kawarabayashi (1978) found that membrane properties of both 128 SMOOTH MUSCLES OF PLACENTAL REGION muscle layers in rat and mouse myometria differ not only in the electrical activity but also in drug sensitivity. For example, the longitudinal muscle possesses only inhibitory fi-adrenoreceptor while the circular muscle has both excitatory a-and inhibitory fi-adrenoreceptors.…”

Inhibitory Action of Human and Rat Placental Extracts on Myometrial Activities of Mouse and Rat

“…In order to reach the circular muscle cell, endometrium was carefully removed and a microelectrode was inserted from the endometrial side of the strip. Mechanical records traced by lower beam were made for muscle strips which were prepared along or transversly to the longitudinal axis of the uterine horn, so that the force generation of the muscle cells belonging to the longitudinal or circular muscle layers respectively was represented (OSA, 1974). As has been shown by previous investigators (MARSHALL, 1959;CASTEELS and KURIYAMA, 1965;OHASHI, 1970;ABE, 1971), the spontaneous electrical activity of the rat longitudinal muscle showed a train discharge of spike potentials supermounted on a slow potential, the membrane potential ranging between 50-60 mV The microelectrodes were advanced from the serosal or endometrial side of the strips for penetrating the longitudinal or circular muscles, respectively.…”

“…It was suggested in a previous paper that a myogenic conduction of excitation may occur between the longitudinal and circular muscle layers of pregnant mouse myometrium, and a postulate was made that such a mechanism may play an important role in performing orderly function of uterine movement as a contractile tubular system (OSA, 1974). It was again found in the present experiment that electrical responses of the pregnant rat myometrium were distinguishable between the longitudinal and circular muscle cells, i. e. spike activity dominated the former cell whereas slow potential did the latter.…”