Calcium influx through receptor-operated channel induces mitochondria-triggered paraptotic cell death

We address the specific role of cytoplasmic Ca2+ overload as a cell death trigger by expressing a receptor-operated specific Ca2+ channel, vanilloid receptor subtype 1 (VR1), in Jurkat cells. Ca2+ uptake through the VR1 channel, but not capacitative Ca2+ influx stimulated by the muscarinic type 1 receptor, induced sustained intracellular [Ca2+] rises, exposure of phosphatidylserine, and cell death. Ca2+ influx was necessary and sufficient to induce mitochondrial damage, as assessed by opening of the permeability transition pore and collapse of the mitochondrial membrane potential. Ca2+- induced cell death was inhibited by ruthenium red, protonophore carbonyl cyanide m-chlorophenylhydrazone, or cyclosporin A treatment, as well as by Bcl-2 expression, indicating that this process requires mitochondrial calcium uptake and permeability transition pore opening. Cell death occurred without caspase activation, oligonucleosomal/50-kilobase pair DNA cleavage, or release of cytochrome c or apoptosis inducer factor from mitochondria, but it required oxidative/nitrative stress. Thus, Ca2+ influx triggers a distinct program of mitochondrial dysfunction leading to paraptotic cell death, which does not fulfill the criteria for either apoptosis or necrosis.