Diets enriched in omega-3 fatty acids exert antiinflammatory properties by suppressing some neutrophil (PMN) functions. Changes in cytosolic Ca2+ concentration, [Ca2+]i, are important for PMN activation and are in part regulated by membrane Ca2+ ATPases. Since membrane proteins are influenced by their lipid environment, we investigated the in vitro effects of the omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on the [Ca2+]i of PMNs in response to f-Met-Leu-Phe (FMLP), leukotriene B4 (LTB4), and ionomycin. The resting [Ca2+]i of PMNs (in high Ca2+ environment) was increased after pretreatment (37 degrees C, 2 h) with DHA, but not with EPA, or the other fatty acids, oleic acid (OA), or linolenic acid (LA). The stimulated [Ca2+]i by either FMLP or LTB4 was suppressed in a high Ca2+ environment after pretreatment with either EPA or DHA but not with OA or LA. The stimulated [Ca2+]i rise by ionomycin was augmented after pretreatment with DHA but not with EPA, OA, or LA. Pretreatment of PMNs with either EPA or DHA reduced the receptor expression for both FMLP and LTB4. Since omega-3 fatty acids inhibit the expression of receptors for two activators of PMNs, FMLP and LTB4, as well as the [Ca2+]i rise in response to those two stimuli, we propose that the antiinflammatory properties of EPA and DHA may be attributed, at least in part, to alteration in membrane activation of phagocytes.