Local Ca²⁺ influx through Ca²⁺ release-activated Ca²⁺ (CRAC) channels stimulates production of an intracellular messenger and an intercellular pro-inflammatory signal

Ca²⁺ entry through store-operated Ca²⁺ channels drives the production of the pro-inflammatory molecule leukotriene C₄ (LTC₄) from mast cells through a pathway involving Ca ²⁺-dependent protein kinase C, mitogen-activated protein kinases ERK1/2, phospholipase A₂, and 5-lipoxygenase. Here we examine whether local Ca²⁺ influx through store-operated Ca²⁺ release-activated Ca²⁺ (CRAC) channels in the plasma membrane stimulates this signaling pathway. Manipulating the amplitude and spatial extent of Ca²⁺ entry by altering chemical and electrical gradients for Ca²⁺ influx or changing the Ca²⁺ buffering of the cytoplasm all impacted on protein kinase C and ERK activation, generation of arachidonic acid and LTC₄ secretion, with little change in the bulk cytoplasmic Ca²⁺ rise. Similar bulk cytoplasmic Ca²⁺ concentrations were achieved when CRAC channels were activated in 0.25 mM external Ca²⁺ versus 2 mM Ca²⁺ and 100 nM La³⁺, an inhibitor of CRAC channels. However, despite similar bulk cytoplasmic Ca²⁺, protein kinase C activation and LTC₄ secretion were larger in 2 mM Ca²⁺ and La³⁺ than in 0.25 mM Ca ²⁺, consistent with the central involvement of a subplasmalemmal Ca²⁺ rise. The nonreceptor tyrosine kinase Syk coupled CRAC channel opening to protein kinase C and ERK activation. Recombinant TRPC3 channels also activated protein kinase C, suggesting that subplasmalemmal Ca²⁺ rather than a microdomain exclusive to CRAC channels is the trigger. Hence a subplasmalemmal Ca²⁺ increase in mast cells is highly versatile in that it triggers cytoplasmic responses through generation of intracellular messengers as well as long distance changes through increased secretion of paracrine signals.