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

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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.