Control of Ca2+ influx in human neutrophils by inositol 1,4,5-trisphosphate (IP3) binding: differential effects of micro-injected IP3 receptor antagonists.
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.
Molecular Signalling Group, University Department of Surgery, University of Wales College of Medicine, Heath Park, Cardiff CF4 4XN, U.K.
E V
EV
Davies-Cox
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I
Laffafian
M B
MB
Hallett
D000595:Amino Acid Sequence; D000906:Antibodies / Q000276:immunology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000276:immunology; D003600:Cytosol / Q000378:metabolism; D006493:Heparin / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D053496:Inositol 1,4,5-Trisphosphate Receptors; D017136:Ion Transport; D008845:Microinjections; D008969:Molecular Sequence Data; D011485:Protein Binding; D018160:Receptors, Cytoplasmic and Nuclear / Q000037:antagonists & inhibitors* / Q000276:immunology
D000906:Antibodies; D015220:Calcium Channels; C506926:ITPR1 protein, human; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D015544:Inositol 1,4,5-Trisphosphate; D006493:Heparin; D002118:Calcium