Influx of extracellular Ca²⁺ into human lung mast cells (HLMCs) is essential for the FcεRI-dependent release of preformed granule-derived mediators and newly synthesized autacoids and cytokines. However, the identity of the ion channels underlying this Ca²⁺ influx is unknown. The recently discovered members of the CRACM/Orai ion channel family that carries the Ca²⁺ release–activated Ca²⁺ current are candidates.

To investigate the expression and function of CRACM channels in HLMCs.

CRACM mRNA, protein, and functional expression were examined in purified HLMCs and isolated human bronchus.

CRACM1, -2, and -3 mRNA transcripts and CRACM1 and -2 proteins were detectable in HLMCs. A CRACM-like current was detected following FcεRI-dependent HLMC activation and also in HLMCs dialyzed with 30 μM inositol triphosphate. The Ca²⁺-selective current obtained under both conditions was blocked by 10 μM La³⁺ and Gd³⁺, known blockers of CRACM channels, and 2 distinct and specific CRACM-channel blockers—GSK-7975A and Synta-66. Both blockers reduced FcεRI-dependent Ca²⁺ influx, and 3 μM GSK-7975A and Synta-66 reduced the release of histamine, leukotriene C₄, and cytokines (IL-5/-8/-13 and TNF⍺) by up to 50%. Synta-66 also inhibited allergen-dependent bronchial smooth muscle contraction in ex vivo tissue.

The presence of CRACM channels, a CRACM-like current, and functional inhibition of HLMC Ca²⁺ influx, mediator release, and allergen-induced bronchial smooth muscle contraction by CRACM-channel blockers supports a role for CRACM channels in FcεRI-dependent HLMC secretion. CRACM channels are therefore a potential therapeutic target in the treatment of asthma and related allergic diseases.