Neutrophils signal Ca2+ changes in response to occupancy of G-protein-linked receptors such as the formylated peptide receptor. This Ca2+ signal is composed of two parts, inositol 1,4,5-trisphosphate (IP3)-triggered release of Ca2+ from an intracellular store and Ca2+ influx. In order to probe the relationship between these events, cytosolic free Ca2+ changes in neutrophils were monitored after micro-injection of agents which inhibit IP3 binding. Micro-injection of heparin into neutrophils totally inhibited both formylmethionyl-leucylphenylalanine-induced Ca2+ release and the subsequent Ca2+ influx. This effect was not due to prior depletion of Ca2+ stores. Furthermore, micro-injection with anti-IP3-receptor antibody also inhibited Ca2+ release. However, anti-IP3-receptor antibody and another high-molecular-mass IP3-binding antagonist, heparin–albumin conjugate, failed to inhibit the accompanying Ca2+ influx. It was concluded that two IP3-binding sites exist in neutrophils: one accessible by both heparin and the high-molecular-mass inhibitors of IP3 binding and responsible for Ca2+ release, and another inaccessible to high-molecular-mass molecules and responsible for Ca2+ influx.
Control of Ca2+ influx in human neutrophils by inositol 1,4,5-trisphosphate (IP3) binding: differential effects of micro-injected IP3 receptor antagonists
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Eryl V. DAVIES-COX, Iraj LAFFAFIAN, Maurice B. HALLETT; Control of Ca2+ influx in human neutrophils by inositol 1,4,5-trisphosphate (IP3) binding: differential effects of micro-injected IP3 receptor antagonists. Biochem J 1 April 2001; 355 (1): 139–143. doi: https://doi.org/10.1042/bj3550139
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