Role of calcium in the resumption of meiosis I in bovine oocytes

Ovaries obtained from a local slaughterhouse were brought to the laboratory in saline at 30-32C within 3 h. The cumulus-oocyte complexes were aspirate d from follicles of 2-7 mm in diameter with Ca++- and Mg++-free PBS, and th en were washed thrice and cultured in TCM 199 buffered with 25 mu mol/l Hep es containing different Ca++ modifying reagents for 9h. Following fixation and staining, the oocytes were observed to determine the stage of meiosis. 10 mu mol/l Ca++ chelator EGTA inhibited the occurrence of GVBD significant ly (p<0.01). When plasma membrane calcium channel was blocked by more than 10 mu mol/l verapamil, significantly more oocytes with intact GV were obtai ned than those in control (p<0.05). More than 62.7% of the oocytes cultured in the medium containing EGTA and verapamil were unable to undergo GVBD. I nactivation of Ca++-calmodulin complex by TFP at concentration of 1mol/l or higher inhibits significantly the occurrence of GVBD than that of control (p<0.01). When intracellular Ca++ release was prevented by 100 mu mol/l TMB -8 or endoplasmic reticulum Ca++-ATPase activation was inhibited by 100 mu mol/l thapsigargin, the oocytes were suppressed to proceed GVBD significant ly than those in control (p<0.05 or p<0.01). The occurrence of GVBD in the oocytes was influenced significantly by 50 mu mol/l or more neomycin (p<0.0 5). The results indicate that both extracellular and intracellular calcium are involved in the regulation of meiotic maturation and intracellular calc ium release induced by IP3 may not be the only pathway for meiotic resumpti on in bovine oocytes.