THE INFLUENCE OF GLUCOSE, CUMULUS CELLS, AND METABOLIC COUPLING ON ATP LEVELS AND MEIOTIC CONTROL IN THE ISOLATED MOUSE OOCYTE

The effects of glucose and cumulus cells on oocyte ATP levels and germ inal vesicle breakdown (GVB) in isolated mouse oocytes have been exami ned. Oocyte-cumulus cell complexes or denuded oocytes (DO) from pregna nt mare serum gonadotropin-primed immature mice were cultured in minim um essential medium containing 4 mM hypoxanthine and 1 mM pyruvate, in the absence or presence of 0.55 mM glucose. After 17-18 hr in the pre sence of glucose, ATP in both the oocyte-cumulus cell complexes and oo cytes derived from such complexes (cumulus cell-enclosed oocytes; CEO) was elevated, and less than one-half of the oocytes had resumed matur ation (48% GVB). Removal of glucose caused a decrease in ATP levels in complexes and CEO and reversed the meiotic arrest in CEO (98% GVB), a nd these effects were mimicked by iodoacetate treatment. Higher freque ncies of GVB were observed in glucose-free medium after more than 6 hr of culture, while ATP levels were reduced within 3 hr. Glucose had no effect on ATP levels or the meiotic state of denuded oocytes. Interes tingly, iodoacetate had a stimulatory effect on GVB in DO (86% GVB com pared to 57% in controls), but did not effect ATP levels. Glycerrhetin ic acid, a gap junction uncoupler, completely suppressed oocyte-cumulu s cell coupling in cultured complexes (0.15% coupling compared to 16.6 % in controls) and reversed the inhibitory effect of glucose on oocyte maturation (91 and 95% GVB at 10 and 25 mu M compared to 42% GVB in c ontrols). This agent also prevented follicle-stimulating hormone-induc ed meiotic maturation in dibutyryl cAMP-arrested CEO. These results th us implicate mediation by gap junctions of both inhibitory and stimula tory signals from the cumulus cells. Comparison of ATP levels in spont aneously maturing CEO in vitro with those from oocytes maturing in viv o in response to human chorionic gonadotropin revealed that a decrease in oocyte ATP preceded or accompanied GVB in spontaneously maturing o ocytes but not in those maturing in vivo. The results of this study in dicate that glucose-derived elevation of oocyte ATP contributes to mei otic arrest in cumulus cell-enclosed oocytes that is dependent on pate nt gap junctions. Furthermore, a model for reinitiation of oocyte matu ration is supported in which spontaneous GVB results from cessation or interruption of inhibitory influences, while ligand-provoked GVB is b rought about by the generation of stimulatory signals that override in hibitory input. (C) 1995 Academic Press, Inc.