Regulation of the human cardiac mitochondrial Ca2+ uptake by 2 different voltage-gated Ca2+ channels.

BACKGROUND: Impairment of intracellular Ca(2+) homeostasis and mitochondrial function has been implicated in the development of cardiomyopathy. Mitochondrial Ca(2+) uptake is thought to be mediated by the Ca(2+) uniporter (MCU) and a thus far speculative non-MCU pathway. However, the identity and properties of these pathways are a matter of intense debate, and possible functional alterations in diseased states have remained elusive. METHODS AND
RESULTS: By patch clamping the inner membrane of mitochondria from nonfailing and failing human hearts, we have identified 2 previously unknown Ca(2+)-selective channels, referred to as mCa1 and mCa2. Both channels are voltage dependent but differ significantly in gating parameters. Compared with mCa2 channels, mCa1 channels exhibit a higher single-channel amplitude, shorter openings, a lower open probability, and 3 to 5 subconductance states. Similar to the MCU, mCa1 is inhibited by 200 nmol/L ruthenium 360, whereas mCa2 is insensitive to 200 nmol/L ruthenium 360 and reduced only by very high concentrations (10 micromol/L). Both mitochondrial Ca(2+) channels are unaffected by blockers of other possibly Ca(2+)-conducting mitochondrial pores but were activated by spermine (1 mmol/L). Notably, activity of mCa1 and mCa2 channels is decreased in failing compared with nonfailing heart conditions, making them less effective for Ca(2+) uptake and likely Ca(2+)-induced metabolism.
CONCLUSIONS: Thus, we conclude that the human mitochondrial Ca(2+) uptake is mediated by these 2 distinct Ca(2+) channels, which are functionally impaired in heart failure. Current properties reveal that the mCa1 channel underlies the human MCU and that the mCa2 channel is responsible for the ruthenium red-insensitive/low-sensitivity non-MCU-type mitochondrial Ca(2+) uptake.