Store-Operated Calcium Entry in Human Neutrophils Reflects Multiple Contributions from Independently Regulated Pathways

Abstract

Human polymorphonuclear neutrophil (PMN) responses to G protein-coupled chemoattractants are highly dependent upon store-operated Ca2+ entry (SOCE). Recent research suggests that SOCE currents can be mediated by a variety of related channel proteins of the transient receptor potential superfamily. SOCE has been regarded as a specific response to depletion of cell calcium stores. We hypothesized that net SOCE might reflect the contributions of more than one calcium entry pathway. SOCE was studied in normal human PMN using Ca2+ and Sr2+ ions. We found that PMN SOCE depends on at least two divalent cation influx pathways. One of these was nonspecific and Sr2+ permeable; the other was Ca2+ specific. The two pathways show different degrees of dependence on store depletion by thapsigargin and ionomycin, and differential sensitivity to inhibition by 2-aminoethyoxydiphenyl borane and gadolinium. The inflammatory G protein-coupled chemoattractants fMLP, platelet-activating factor, and IL-8 elicit unique patterns of Sr2+ and Ca2+ influx channel activation, and SOCE responses to these agonists displayed differing degrees of linkage to prior Ca2+ store depletion. The mechanisms of PMN SOCE responses to G protein-coupled chemoattractants are physiologically diverse. They appear to reflect Ca2+ transport through a variety of channels that are independently regulated to varying degrees by store depletion and by G protein-coupled receptor activation.

Intracellular Calcium Waves Accompany Neutrophil Polarization, Formylmethionylleucylphenylalanine Stimulation, and Phagocytosis: A High Speed Microscopy Study

“…One likely participant is inositol 1,4,5-triphosphate, which is generated during FMLP stimulation of neutrophils (54). Inositol 1,4,5-triphosphate promotes Ca 2ϩ release from the ER, which in turn triggers store-operated Ca 2ϩ influx across the plasma membrane (55). Recently, phosphoinositol 3-kinase-␥ knockout mice have been shown to be defective in orientation in the presence of a chemotactic factor (56); this defect may be associated with the second clockwise Ca 2ϩ wave.…”

Free Cholesterol Alters Lipid Raft Structure and Function Regulating Neutrophil Ca2+ Entry and Respiratory Burst: Correlations with Calcium Channel Raft Trafficking

“…Blood was spun (150 ϫ g for 10 min) to remove platelet-rich plasma. Cells were then layered onto equal volumes of Polymorphoprep medium (Robbins Scientific) and separated as we have described (8,17,22). PMN layers were removed and mixed with an equal volume of 0.45% sodium chloride solution to restore osmolarity for 5 min.…”

“…PMN lack voltage-gated calcium channels (19) and we have shown that PMN mobilize external Ca 2ϩ via mechanisms that mobilize multiple TRPC proteins to the cell membrane (8,9). Cytoskeletal alterations that prevent TRPC membrane localization block entry of calcium into PMN (9) and TRPC are known to localize to rafts in PMN and other cell types (20,21).…”

“…These conductances can be referred to as "store-operated", "capacitative," or "calcium release-activated" calcium entry (SOCE/CCE/I CRAC ) depending upon the channel characteristics noted in specific experimental systems. But the increases in [Ca 2ϩ ] i that activate native cells in vivo are often due to activation of multiple related conductances that contribute to "stimulated calcium entry" (7)(8)(9). Transient receptor potential channel (TRPC) proteins can form cation channels that are activated when G protein-coupled receptors (GPCR) linked to phospholipases release diacylglycerol and inositol 1,4,5 trisphosphate and deplete cell calcium stores (10 -12).…”

Inhibitory Mechanism of Store-operated Ca2+ Channels by Zinc

“…The cation influx mediated by SOCC is highly Ca 2ϩ -specific. Other divalent cations such as Ba 2ϩ and Sr 2ϩ are also permeable albeit at a much slower rate (3,7). In the absence of divalent cations, it has been reported that the SOCC becomes permeable to Na ϩ (8,9).…”