The changes of Cx-43 and MAP kinase in cumulus cells that were recovered from porcine cumulus oocyte complexes (COCs) cultured with FSH and LH and/or PI 3-kinase inhibitor, LY294002, were analyzed by immunoblotting. Three migration forms of Cx-43 (43, 45, and 47 kDa) were detected in the cumulus cells of COCs immediately recovered from their follicles. At 12-hr of cultivation with hormones, oocyte nuclear stage was progressed from GV II stage to GV III stage. At this time point, the 43 kDa band almost completely disappeared, although two phosphorylation forms of Cx-43 (45 and 47 kDa) were still detected. However, in the cumulus cells of COCs cultured with LY294002, three prominent bands of Cx-43 were recognizable, as in the cells recovered immediately from the follicles. Although two intense bands of activated MAP kinase (ERK 1, 2) were also seen in the cumulus cells of COCs at 12-hr of cultivation with hormones, the intensity of the activated ERK 2 band was relatively faint in cumulus cells of COCs cultured with LY294002. At the same time point, LY294002 produced a significant decrease in the proportion of oocytes exhibiting GV III stage compared to those observed with hormones. It is concluded that the progression from GV II stage to GV III stage in porcine oocytes may be closely associated with phosphorylation of Cx-43 by virtue of MAP kinase, which was activated through the PI 3-kinase pathway in their cumulus cells.