Calcium influx through SOCE and Orai1 facilitates neutrophil arrest. (A) PMNs isolated from murine Orai1−/+, WT littermates (ie, Orai1+/+), 2-day differentiated HL-60 cells, or freshly isolated human PMNs were loaded with fura-2, incubated with 1 μM thapsigargin as indicated, and then perfused over a monolayer of L cells expressing E-selectin and ICAM-1 in the presence of 0.1mM ethyleneglycoltetraacetic acid. At time 0, 1.5mM CaCl₂ was injected into the inlet reservoir triggering selectin-dependent rolling and calcium influx through store-operated calcium channels. (A) Panels indicate intracellular calcium concentration and arrested fraction from WT or Orai1−/+ PMNs as indicated. (B) HL-60 cells were transfected with scrambled control or specific Orai1 siRNA as indicated (both n = 10). Orai1 siRNA-transfected cells had significantly higher rolling fractions at 150 seconds, 160 seconds, and 170 seconds (P = .03, .01, and .03, respectively) than control transfected cells. (C) Human PMNs were analyzed in the presence of vehicle control (n = 6), 100μM 2-APB (n = 4), or 1μM U73122 (n = 4) as a function of time. Cells treated with 2-APB had significantly lower arrest fraction than control at 60 seconds (P = .01). All statistical comparisons in this figure are by 2-tailed t test: *P < .05; **P < .01.