Cav1.2 L-type Ca2+ channel protects mast cells against activation-induced cell death by preventing mitochondrial integrity disruption

In non-excitable cells, store-operated Ca2+ channels (SOCs) are the principal routes of Ca2+ entry. Recently, store-independent Ca2+ channels which are pharmacologically and/or immunologically similar to L-type Ca2+ channels (LTCCs) have been shown to exist in various hematopoietic cells, including T cells, B cells and neutrophils. We previously reported that mast cells express LTCCs which regulate mast cell effector responses in a distinct manner from SOCs. In the present study, we examined the possible role for LTCCs in mast cell survival. Both RBL-2H3 mast cells and bone marrow-derived mast cells underwent considerable apoptosis after treatment with thapsigargin (Tg) but not stimulation through the high-affinity IgE receptor (FcɛRI). The LTCC-selective antagonists such as nifedipine greatly augmented FcɛRI-mediated apoptosis, while the LTCC-selective agonist (S)-BayK8644 blocked Tg-induced apoptosis. The modulation of apoptosis was accompanied by altered mitochondrial integrity, as measured with the mitochondrial membrane potential, cytochrome c release and caspase-3/7 activation. FcɛRI stimulation induced mitochondrial Ca2+ ([Ca2+]m) entry through both SOCs and LTCCs, while Tg evoked [Ca2+]m entry through LTCCs but not SOCs. The LTCC-selective antagonists blocked [Ca2+]m entry, whereas (S)-BayK8644 augmented Tg-induced [Ca2+]m entry. Moreover, blockade of the expression of the α1C subunit of Cav1.2 LTCC using small-interfering RNA strongly augmented FcɛRI-mediated apoptosis, mitochondrial integrity, and mitochondrial Ca2+ collapse, and abolished the protective effects of (S)-BayK8644 against Tg-induced apoptosis. These findings suggest that Cav1.2 LTCC protects mast cells against activation-induced cell death by preventing mitochondrial integrity disruption.