| Oocyte growth, meiotic maturation, and follicle development are complex and incompletely understood processes. The goal of this study was to comprehensively survey amino acid transport system activities in oocytes and in follicular cells at all stages of development in order to better understand these processes as well as how the oocyte becomes independent of the metabolic support of the follicular cells. Tests were designed to identify transport activities corresponding to the classical amino acid transport systems GLY, beta, N, A, ASC/asc, XAG-, B0,+, CAT, L, x c- and b0,+. Transport measurements of radiolabelled substrates of these systems were performed in the absence and in the presence of specific competitive inhibitors to measure uptake activity consistent with that of the systems. It was found that there were transport activities consistent with systems GLY, beta, ASC/asc, L, xc - and b0,+ in oocytes throughout growth and maturation. The activities consistent with systems GLY, beta and xc -, however, only fully developed during meiotic maturation, possibly at a time when the substrates of these transport systems have specific functions. On the contrary, activities consistent with systems A, XAG -, B0,+ and CAT were not detected in oocytes at any stage of development. Amino acid substrates of systems GLY, beta, ASC/asc, L and b0,+ were also detected in isolated follicular cells. All of these transport systems, except for L, mediated cooperative amino acid transport into oocytes at levels dependent on developmental stage, while system L transport activity was inhibited by the presence of follicular cells. |
