The structural and biochemical characteristics of ovarian granulosa cell plasma membranes will be studied during the course of follicular development and ovulation in the mammal. Electron microscopic morphometry will be used to quantitate the time of appearance, growth, and internalization of granulosa cell gap junctions in rabbits and rats after priming with estrogens and/or FSH and LH. Both freeze fracture and transmission electron microscopy will be used to determine the structural changes in granulosa cell gap junctions which occur in response to gonadotropins, and how cytoskeletal elements participate in the process of gap junction internalization. Using primary cultures of rat granulosa cells, the pattern of movement and endocytosis of cell surface receptors for lectins and gonadotropins will be followed in conjunction with the use of antibodies raised against the cytoskeletal proteins tubulin, actin and myosin. The role of cytoskeletal structures in the determination of receptor movement and uptake as well as the control of cellular shape will be studied in detergent extracted cultured granulosa cells and with isolated plasma membranes. These studies are aimed at elucidating the mechanism of gonadotropin action on granulosa cells which occurs during follicular development and ovulation.