The purpose of this study is to investigate the involvement of protein kinase C (PKC) in prostaglandin E2 (PGE2)-stimulated cAMP production of two macrophage-like cell lines (G3 and XC). XC cells are thought to be placed at a more differentiated stage than G3 cells [Orikasa et al. (1991) Cell Immunol. 132, 350-365]. In RPMI 1640 containing 10% (v/v) heat-inactivated foetal calf serum (FCS), in which the cAMP response of both cells to PGE2 increased with duration of culture, XC cells showed greater response than G3 cells at 2 days of culture. In alpha-minimum essential medium (alpha-MEM) containing 20% (v/v) heat-inactivated horse serum (HS), the cAMP response of both cells was apparently greater than that in RPMI 1640 containing 10% (v/v) FCS. These cells increased cAMP production also in response to PGE1 and PGF2 alpha, and the order of potency in increase was PGE1 > PGE2 >> PGF2 alpha. Interestingly, a short-term (20 min) treatment with phorbol 12-myristate 13-acetate (PMA), a direct activator of PKC or staurosporine, a relatively specific inhibitor of PKC, augmented the PGE2-stimulated cAMP production in these cells cultured in alpha-MEM containing 20% (v/v) HS. However, a long-term (24 h) treatment with these compounds did not alter the cAMP response. In G3 cells, PMA appeared more potent than staurosporine in terms of augmentation, whereas in XC cells, the former appeared less potent than the latter.(ABSTRACT TRUNCATED AT 250 WORDS)