L-type Ca2+ channels in mast cells: Activation by membrane depolarization and distinct roles in regulating mediator release from store-operated Ca2+ channels

Abstract

Store-operated Ca2+ channels (SOCs) are considered to be the principal route of Ca2+ influx in non-excitable cells. We have previously shown that in mast cells IgE+antigen (Ag) induces a dihydropyridine (DHP)-sensitive Ca2+ influx independently of Ca2+ store depletion. Since the DHP receptor is the α subunit of L-type Ca2+ channels (LTCCs), we examined the possible role of LTCCs in mast cell activation. Mast cells exhibited substantial expression of the α1C (CaV1.2) subunit mRNA and protein on their cell surface. IgE+Ag-induced Ca2+ influx was substantially reduced by the LTCC inhibitor nifedipine, and enhanced by the LTCC activator (S)-BayK8644, whereas these agents had minimal effects on thapsigargin (TG)-induced Ca2+ influx. These LTCC-modulating agents regulated IgE+Ag-induced cell activation but not TG-induced cell activation. Inhibition of SOCs by 2-aminoethoxydiphenyl borate reduced both degranulation and production of cytokines, including interleukin-13 and tumor necrosis factor-α, whereas LTCC modulation reciprocally regulated degranulation and cytokine production. IgE+Ag, but not TG, induced substantial plasma membrane depolarization, which stimulated a DHP-sensitive Ca2+ response. Moreover, IgE+Ag-, but not TG-induced mitochondrial Ca2+ increase was regulated by LTCC modulators. Finally, gene silencing analyses using small interfering RNA revealed that the α1C (CaV1.2) LTCC mediated the pharmacological effects of the LTCC-modulating agents. These results demonstrate that mast cells express LTCCs, which becomes activated by membrane depolarization to regulate cytosolic and mitochondrial Ca2+, thereby controlling mast cell activation in a distinct manner from SOCs.