Biphasic formation of inositol phosphates in opsonized zymosan-stimulated human neutrophils

• Published in: Cellular signalling Vol. 7; no. 4; pp. 397 - 402
• Main Authors: Leino, Lasse, Tuominen, Helena, Lehtola, Kirsi, Åkerman, Karl E.O., Punnonen, Kari
• Format: Journal Article
• Language: English
• Published: England Elsevier Inc 01.05.1995
• Subjects: Blood; calcium; Calcium - metabolism; Fluorescent Dyes; Fura-2 - analogs & derivatives; Humans; Inositol 1,4,5-Trisphosphate - biosynthesis; Inositol phosphates; Inositol Phosphates - biosynthesis; Kinetics; neutrophils; Neutrophils - drug effects; Neutrophils - metabolism; Opsonin Proteins; receptors; Signal Transduction; zymosan; Zymosan - pharmacology; calcium; CR—complement receptor; receptors; InsP 4—inositol tetrakisphosphate; signal transduction; Inositol phosphates; [Ca 2+] i—cytosolic free Ca 2+ concentration; InsP 3—inositol trisphosphate; InsP—inositol phosphate; SOZ—serum-opsonized zymosan; FcR—Fc receptor for immunoglobulin G; zymosan; neutrophils
• ISSN: 0898-6568; 1873-3913
• DOI: 10.1016/0898-6568(94)00094-R

Stimulation by serum-opsonized zymosan (SOZ) typically causes a biphasic rise in the cytosolic free Ca 2+ concentration ([Ca 2+] i) of human neutrophils. It consists of an initial slow Ca 2+ release from internal pools lasting for 60 s, followed by a rapid but sustained influx of Ca 2+. It was the aim of this study to elucidate the underlying mechanism of this atypical Ca 2+ response. For this reason we analysed the production of inositol phosphates (InsPs) in myo-[ 3H]inositol labelled cells. Stimulation by SOZ within 10 s transiently elevated inositol trisphosphate (InsP 3) by 1.50-fold. This response was followed by a second, more sustained 1.55-fold rise in InsP 3 by 90 s. A similar, biphasic pattern of inositol tetrakisphosphate (InsP 4) formation with 1.15- and 1.35-fold increases, respectively, was observed. The SOZ-induced formation of InsP 3 was unaffected by the removal of extracellular Ca 2+ by 1.4 mM EGTA. In contrast, the early accumulation of InsP 4 was stronger and more prolonged and no second rise over the baseline level was seen in the absence of extracellular Ca 2+. Under these conditions, the sudden exposure of Fura-2 AM loaded, SOZ-stimulated neutrophils to extracellular Ca 2+ at a time point where InsP 4 was the predominant InsP resulted in a marked increase in [Ca 2+] i. Recalcification at a time point when InsP 3 was the major InsP had no effect on [Ca 2+] i. These findings suggest that in SOZ-stimulated neutrophils (1) the transient, first accumulation of InsP 3 mediates the slow Ca 2+ release from internal pools, and (2) the second, more pronounced formation of InsP 4 triggers the Ca 2+ influx. It is hypothesised that the unusual second messenger response to SOZ stimulation may reflect the activation of several receptor types coupled to parallel signalling pathways.