Metabolic, fluorescent dye and electrical coupling between hamster oocytes and cumulus cells during meiotic maturation in vivo and in vitro

Abstract

Heterologous intercellular communication was determined qualitatively by lucifer yellow dye transfer and quantitatively by transfer of radiolabeled uridine metabolites and electrical current in hamster oocyte-cumulus complexes during meiotic maturation in vitro and in vivo. In addition, changes in cell resting potentials during maturation were recorded. Significantly less time was required for germinal vesicle breakdown (GVBD) in oocytes matured in vitro than in oocytes stimulated in vivo (1.81 ± 0.06 hr, N = 13 vs 2.46 ± 0.07 hr, N = 18, respectively, P < 0.001). Resting potentials of the oocyte (RP-o) and cumulus cells (RP-c) significantly increased contemporaneously with GVBD in vitro (RP-o: from −18.9 ± 3.2 mV to −33.2 ± 2.9 mV, P < 0.001; RP-c: from −16.3 ± 1.9 mV to −27.5 ± 2.6 mV, P < 0.001) and in vivo after hCG injection (RP-o: from −16.8 ± 5.9 mV to −30.1 ± 3.9 mV, P < 0.001; RP-c: from −15.5 ± 3.8 mV to −26.3 ± 3.2 mV, P < 0.001). RP-o and RP-c progressively increased with time of culture up to 7 hr (maximum time examined) while the values reached maxima in in vivo matured oocytes 4.5 hr post-hCG and subsequently declined concomitant with the onset of cumulus expansion. Cumulus to oocyte coupling decreased progressively with time after release from meiotic arrest both in vitro and in vivo, as assessed by a progressive reduction in transfer of either uridine marker or lucifer yellow from the cumulus cell to the oocyte. By 4.5 hr after hCG injection, cumulus expansion had begun in 100% of complexes examined. Expansion was extensive by 7 hr post-hCG and spread of lucifer yellow from a cumulus cell was limited to very few adjacent cumulus cells. Oocyte to cumulus cell metabolic coupling also decreased progressively with time in both treatment groups. Examination of the extent of heterologous ionic coupling revealed that ionic coupling exhibited biphasic and, bidirectionally parallel, increases during meiotic maturation. While these temporal changes were observed in both groups, the coupling ratios were much greater in those complexes matured in vitro than in vivo. These results show that dye, metabolic, and electrical coupling exist between the immature hamster oocyte and its surrounding cumulus cells but that during the early stages of meiosis, metabolic and dye coupling decrease, while electrical coupling increases biphasically.