Cyclosporin A Increases Mitochondrial Buffering of Calcium: An Additional Mechanism in Delaying Mitochondrial Permeability Transition Pore Opening

摘要

Regulation of mitochondrial free Ca²⁺ is critically important for cellular homeostasis. An increase in mitochondrial matrix free Ca²⁺ concentration ([Ca²⁺]m) predisposes mitochondria to opening of the permeability transition pore (mPTP). Opening of the pore can be delayed by cyclosporin A (CsA), possibly by inhibiting cyclophilin D (Cyp D), a key regulator of mPTP. Here, we report on a novel mechanism by which CsA delays mPTP opening by enhanced sequestration of matrix free Ca²⁺. Cardiac-isolated mitochondria were challenged with repetitive CaCl2 boluses under Na⁺-free buffer conditions with and without CsA. CsA significantly delayed mPTP opening primarily by promoting matrix Ca²⁺ sequestration, leading to sustained basal [Ca²⁺]m levels for an extended period. The preservation of basal [Ca²⁺]m during the CaCl2 pulse challenge was associated with normalized NADH, matrix pH (pHm), and mitochondrial membrane potential (ΔΨm). Notably, we found that in PO4³⁻ (Pi)-free buffer condition, the CsA-mediated buffering of [Ca²⁺]m was abrogated, and mitochondrial bioenergetics variables were concurrently compromised. In the presence of CsA, addition of Pi just before pore opening in the Pi-depleted condition reinstated the Ca²⁺ buffering system and rescued mitochondria from mPTP opening. This study shows that CsA promotes Pi-dependent mitochondrial Ca²⁺ sequestration to delay mPTP opening and, concomitantly, maintains mitochondrial function.