The ratio of macrophage prostaglandin and leukotriene synthesis is determined by the intracellular free calcium level

Abstract

The induction of eicosanoid synthesis in various cell types by different physiological stimuli is dependent on an increase in the intracellular calcium level and stimulation of the protein kinase C (PKC). In a model system this can be mimicked by using calcium ionophores and direct PKC activators. In mouse peritoneal macrophages calcium ionophores induced the formation of prostaglandin E 2 (PGE 2) and leukotriene C 4 (LTC 4). A synergistic enhancement of both eicosanoids could be achieved by simultaneous addition of the calcium ionophore A23187 together with a suboptimal dose of the direct protein kinase C activator 12- O-tetradecanoylphorbol 13-acetate (TPA). Low concentrations of the ionophore, resulting in only marginally increased intracellular calcium levels, led to a more than additive prostaglandin E 2 production in combination with TPA. Higher concentrations of A23187 together with TPA favoured LTC 4 synthesis, whereas PGE 2 levels at the same time were even diminished. This observed shift from prostaglandin to leukotriene formation was amplified by simultaneous addition of indomethacin. Manganese as inhibitor of the A23187-induced calcium influx decreased PGE 2 synthesis. On the other hand, in the presence of manganese LTC 4 production was also inhibited at high concentrations of A23187 but elevated in the absence or at low doses of A23187. Our data provide evidence that in macrophages the ratio of cyclooxygenase and lipoxygenase products caused by mediators, acting via the phospholipase C or D/PKC signal transduction pathway, is regulated by the extent of the intracellular calcium increase.