Mitochondrial channels permeable by calcium ions.

The aim of this work was to characterize inner mitochondrial membrane channels permeable to calcium cations (Ca(++)). Mitochondrial membranes isolated from rat heart were incorporated into the bilayer lipid membrane, and single Ca(++) channel currents were measured. The observed channels were selective for Ca(++) and barium cations (Ba(++)) (53 and 50 mM) over Tris(+) (113 mM), but single-channel currents in most cases were noisy and did not show the typical single-channel shape, as it is known, for example, in the ryanodine receptor or in inositol 1,4,5-trisphosphate (IP(3)R) Ca(++)-release channels. The most commonly observed single-channel currents, measured at the 0 mV and 53 mM Ca(++) gradient, were in the range of 1 pA or less. The channels responded to pharmacological modulators. Some of the channels were inhibited by ruthenium red and cyclosporin A, and others were modulated by ryanodine. This may indicate that the observed channels passing Ca(++) may originate from the mitochondrial Ca(++) uniporter, the permeability transition pore, and the ryanodine receptor calcium channel.