Mechanisms involved in the cytosolic calcium ion elevation induced by activating factors in chicken and rat phagocytes
Yong, Sheng | ABE, Asaki | KONDO, Yasuhiro
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.
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