The mitochondrial calcium uniporter is a highly selective ion channel

Abstract

During intracellular Ca2+ signalling mitochondria accumulate significant amounts of Ca2+ from the cytosol. Mitochondrial Ca2+ uptake controls the rate of energy production, shapes the amplitude and spatio-temporal patterns of intracellular Ca2+ signals, and is instrumental to cell death. This Ca2+ uptake is undertaken by the mitochondrial Ca2+ uniporter (MCU) located in the organelle's inner membrane. The uniporter passes Ca2+ down the electrochemical gradient maintained across this membrane without direct coupling to ATP hydrolysis or transport of other ions. Carriers are characterized by turnover numbers that are typically 1,000-fold lower than ion channels, and until now it has been unclear whether the MCU is a carrier or a channel. By patch-clamping the inner mitochondrial membrane, we identified a previously unknown Ca2+-selective ion channel sensitive to inhibitors of mitochondrial Ca2+ uptake. Our data indicate that this unique channel binds Ca2+ with extremely high affinity (dissociation constant < or =2 nM), enabling high Ca2+ selectivity despite relatively low cytoplasmic Ca2+ concentrations. The channel is inwardly rectifying, making it especially effective for Ca2+ uptake into energized mitochondria. Thus, we conclude that the properties of the current mediated by this novel channel are those of the MCU.

Differential oxidative stress in oligodendrocytes and neurons after excitotoxic insults and protection by natural polyphenols

“…Excitotoxic death is dependent primarily on Ca 21 entry into the cell by ionotropic glutamate receptors (Alberdi et al, 2002;Krieger and Duchen, 2002). An increase in cytosolic Ca 21 concentration depolarizes mitochondria which possess a high-affinity Ca 21 uniporter on their inner membrane (Kirichok et al, 2004). Accordingly, activation of AMPA and kainate receptors in oligodendrocytes induces a large increase in the concentration of cytosolic Ca 21 , the bulk of which is rapidly sequestered by mitochondria (Sanchez-Gomez et al, 2003).…”

Excitation-contraction coupling and mitochondrial energetics

“…From experiments on suspensions of isolated mitochondria, a half-maximal activation constant (K 0.5 ) of ∼10-20 µM Ca 2+ was calculated for mCU-mediated Ca 2+ transport, yielding a maximum Ca 2+ flux (V max ) of approximately 2·10 4 Ca 2+ s −1 for a single mCU molecule [76,77]. The mCU is inhibited by ruthenium red [124,138,157] or Ru360 [109,117,124], with the latter being more mCUselective than ruthenium red [124], which also inhibits SR Ca 2+ release via RyR2 [35]. Furthermore, dissipation of Δψ m by agents that uncouple respiration (i.e., a combination of FCCP and oligomycin) also inhibits mitochondrial Ca 2+ uptake by reducing the driving force for Ca 2+ entry (Δψ m ) rather than interacting with the mCU itself.…”

Mitochondrial Ca 2+ Influx Contributes to Arrhythmic Risk in Nonischemic Cardiomyopathy

“…The mitochondrial and cytosolic fraction was obtained from the supernatant by centrifugation at 10 700 g for 10 minutes twice. The pellet was resuspended in 500 μL of buffer without EGTA (pH 7.2 with KOH) 10, 21…”

“…Measured currents included the L‐type Ca 2+ current (I Ca,L ),23 K + current,24 and NCX current 25. MCU current (I MCU ) was recorded in the whole‐mitoplast voltage clamp configuration 10, 21…”

“…I MCU was recorded in whole‐mitoplast voltage clamp configuration 10, 21. Mitoplasts were perfused with solution containing the following (mmol/L): Na gluconate 150, HEPES 10, and CaCl 2 5 (pH 7.4, adjusted with NaOH).…”