The physiological activity of uterine smooth muscle can be regulated through alterations in the electrical properties of the myometrial cells. During most of gestation, the uterus is kept in a relatively quiescent state, but at term, the myometrium is prepared for the intense activity of labor by processes involving changes in its electrical properties. Increased activation by physiological estrogen, for example, is believed to play a crucial role in the preparation of the myometrium at term pregnancy for the intense activity of labor. The enhancement of electrical excitability by estrogen involves increased expression of gap junctions and membrane receptors, and recently, it was shown that estrogen may control the synthesis of voltage-dependent ion channels in rat myometrial cells. In addition, the presence of excitatory substances such as oxytocins and prostaglandins around the time of labor cause an immediate and rapid intensification of activity through direct effects of the muscle. The main overall objectives of the proposed studies would be to study the control of voltage-dependent ion channel expression in human myometrial cells, and to begin using isolated human myometrial cells for electrophysiological studies of agents involved in short- and long-term regulation of ion channel behavior. Using molecular biological techniques, including both the Xenopus oocyte expression system and Northern blotting, the detection of an mRNA species from human myometrial tissue similar to the one which was found in rat uterine RNA and shown capable of inducing the expression of potassium channels in oocytes will be attempted. In addition, primary cultures of isolated myometrial cells will be prepared and characterized. Spontaneous and evoked action potential activity will be studied using current-clamp techniques. The types of potassium ion channels expressed in these cells will be studied using patch techniques, Experiments will be done to determine whether very slowly activating potassium channels like those present in rat visceral smooth muscle can be detected in isolated human myometrial cells. The electrophysiological effects of rapidly acting excitatory substances such as peptides (oxytocin, EGF) and prostaglandins will be studied. The responses to compounds such as estrogen which require a longer period of exposure to exert their effects will also be examined in vitro using the cultured cells. In particular, the hypothesis that estrogen may increase the density of slowly activating potassium channels in these cells will be tested. Studies such as these are likely to provide insight into molecular events underlying normal and abnormal labor. It seems likely that potassium channels which show tissue-specific expression or regulation of pharmacological agents which could be used clinically.
