Role of Calcium in the Resumption of Meiosis I in Bovine Oocytes

Abstract

Liu, L., Zhang, H., Qian, J. and Fujihara, N. 1999. Role of calcium in the resumption of meiosis I in bovine oocytes. J. Appl. Anim. Res., 15: 97–104. Ovaries obtained from a local slaughterhouse were brought to the laboratory in saline at 30–32C within 3 h. The cumulus-oocyte complexes were aspirated from follicles of 2- 7 mm in diameter with Ca++- and Mg**- free PBS, and then were washed thrice and cultured in TCM 199 buffered with 25μmol/l Hepes containing different Ca** modifying reagents for 9h. Following fixation and staining, the oocytes were observed to determine the stage of meiosis. lOμmol/l Ca++ chelator EGTA inhibited the occurrence of GVBD significantly (p<0.01). When plasma membrane calcium channel was blocked by more than lOμmol/l verapamil, significantly more oocytes with intact GV were obtained 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. Inactivation of Ca++- calmodulin complex by TFP at concentration of lmol/l or higher inhibits significantly the occurrence of GVBD than that of control (p<0.01). When intracellular Ca++ release was prevented by lOOμmol/l TMB-8 or endoplasmic reticulum Ca++- ATPase activation was inhibited by lOOμmol/l thapsigargin, the oocytes were suppressed to proceed GVBD significantly than those in control (p<0.05 or p<0.01). The occurrence of GVBD in the oocytes was influenced significantly by 50μmol/l or more neomycin (p<0.05). The results indicate that both extracellular and intracellular calcium are involved in the regulation of meiotic maturation and intracellular calcium release induced by IP3 may not be the only pathway for meiotic resumption in bovine oocytes.