Effects of estradiol-17 beta on the membrane response and K-contracture in the uterine longitudinal muscle of ovariectomized rats studied in combination with the Mn action.

The membrane potential was about --50mV, and the spontaneous membrane activity was composed of an irregular discharge of action potentials in the longitudinal muscle of the ovariectomized rat uterus. The membrane potential was increased slightly, and repetitive spike potentials were generated on a plateau potential in uteri of ovariectomized rats injected daily with 5 microgram estradiol benzoate, until the steady effect was built up in 3--4 days. The phasic contraction resulted in a relaxation upon exposure to the isotonic K solution containing 2.2 mM Ca, then a tonic contraction developed in ovariectomized uterus. The phasic contraction decayed slightly and it proceeded into a tonic contraction in estrogen-treated uteri. The amplitude of the tonic contraction became larger when the external Ca concentration was raised, and the dose-response relationship shifted to the lower range of the external Ca concentration in the estrogen-treated uterus. In the Ca-depleted solution, the tonic contraction subsided and a contraction was generated when Mn was applied. The change in the configuration of the K-contractures depending on the estrogenic treatment was ascribed to an increase in the Ca influx upon K-depolarization forming greater tonic contraction.