| Growth and development of ovarian follicles is characterized by the gonadotropin-dependent formation and expansion of a fluid-filled cavity, termed the antrum, which requires a large influx of water into the follicle. Since proper development and ovulation of female germ cells is dependent on antrum formation and expansion, the purpose of these studies was to elucidate the mechanisms of gonadotropin-induced water trafficking in antral follicles. To determine whether water influx in developing antral follicles occurs by transcellular or pericellular transport mechanisms, the rate of 3H2O and 14C-inulin uptake into isolated follicles was measured. The rate of H2O movement was 3.5-fold greater than inulin, indicating the water permeability of an antral follicle is approximately 70% transcellular. Furthermore, water channels, called aquaporins (AQPs), were found to mediate this transcellular water transport. Analysis of granulosa cells cultured in the presence and absence of FSH revealed that AQP 8 and 9 expression is increased in response to the gonadotropin. Treatment with inhibitors and activators of FSH signaling pathways revealed that AQP 8 expression is induced by cAMP/PKA, while AQP 9 expression is increased primarily by PKC/MAPK. However, AQPs 8 and 9 were found to be primarily localized to the cytoplasm and thus, non-functional, but co-treatment with serum and FSH increased both translocation of AQP 8 and 9 and plasma membrane water permeability. Together, these results provide evidence for the exquisite regulation of AQP expression and sub-cellular localization in the ovary, suggesting AQPs may play critical roles in water movement during FSH-stimulated antrum formation. |
