Abstract
Heart mitochondria utilize multiple Ca(2+) transport mechanisms. Among them, the mitochondrial ryanodine receptor provides a fast Ca(2+) uptake pathway across the inner membrane to control "excitation and metabolism coupling." In the present study, we identified a novel ryanodine-sensitive channel in the native inner membrane of heart mitochondria and characterized its pharmacological and biophysical properties by directly patch clamping mitoplasts. Four distinct channel conductances of ∼100, ∼225, ∼700, and ∼1,000 picosiemens (pS) in symmetrical 150 mm CsCl were observed. The 225 pS cation-selective channel exhibited multiple subconductance states and was blocked by high concentrations of ryanodine and ruthenium red, known inhibitors of ryanodine receptors. Ryanodine exhibited a concentration-dependent modulation of this channel, with low concentrations stabilizing a subconductance state and high concentrations abolishing activity. The 100, 700, and 1,000 pS conductances exhibited different channel characteristics and were not inhibited by ryanodine. Taken together, these findings identified a novel 225 pS channel as the native mitochondrial ryanodine receptor channel activity in heart mitoplasts with biophysical and pharmacological properties that distinguish it from previously identified mitochondrial ion channels.
Highlights
Mitochondrial Ca2ϩ transport plays critical roles in the regulation of mitochondrial function under both physiological and pathological conditions [1,2,3]
Ryanodine-sensitive Channel Activity in Heart Mitoplasts— To confirm that our mitoplast preparations were derived from cardiac mitochondria, we stained freshly isolated cardiomyocytes with MitoTracker Red CM-H2XRos and examined mitoplasts isolated from these myocytes under a fluorescence microscope
We identified a novel Ca2ϩ-permeable and ryanodine-sensitive mitochondrial channel in heart mitoplasts
Summary
Mitochondrial Ca2ϩ transport plays critical roles in the regulation of mitochondrial function under both physiological and pathological conditions [1,2,3]. The mitochondrial ryanodine receptor provides a fast Ca2؉ uptake pathway across the inner membrane to control “excitation and metabolism coupling.” In the present study, we identified a novel ryanodine-sensitive channel in the native inner membrane of heart mitochondria and characterized its pharmacological and biophysical properties by directly patch clamping mitoplasts.
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