Mechanisms involved in the cytosolic calcium ion elevation induced by activating factors in chicken and rat phagocytes.

The aim of the present study was to determine the mechanism of cytosolic calcium ion concentration [Ca2+]i elevation in chicken and rat phagocytes stimulated with phorbol myristate acetate (PMA), leukotriene B4 (LTB4), formyl-methionyl-leucyl-phenylananine (fMLP) and Saccaromyces cerevisiae culture supernatant (SCS). Pretreatment with EGTA completely suppressed the PMA-induced [Ca2+]i elevation in rat and chicken phagocytes, suggesting that all the [Ca2+]i elevation induced in the PMA-stimulated rat and chicken phagocytes was attributable to the influx of extracellular Ca2+. On the other hand, the elevation of LTB4-, FMLP- and SCS-induced [Ca2+]i was only partially suppressed by ethyleneglycol-bis (β-aminoethyl)-N,N,N′,N′-tetraacetic acid ethylene (EGTA) pretreatment of phagocytes. The results indicated that two pathways of [Ca2+]i elevation, recruitment from the intracellular Ca2+ store and influx of extracellular Ca2+, are involved in the [Ca2+]i elevation of LTB4-, fMLP- and SCS-stimulated phagocytes. In fMLP-stimulated rat neutrophils, [Ca2+]i elevation showed a two-phase pattern in which the time lag between the first and second phase was approximately 1 min. The EGTA treatment of the fMLP-stimulated cells induced a reduction of the first phase level and a disappearance of the second phase. The reason for the special influence of EGTA observed in fMLP-stimulated cells is unknown, but the disappearance of the second phase of the [Ca2+]i may be elicited by the EGTA-induced decrease of the first phase [Ca2+]i elevation that depends on IP3 and diacylglycerol induced by fMLP. [ABSTRACT FROM AUTHOR]