Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
10798079 | Biochimica et Biophysica Acta (BBA) - Biomembranes | 2007 | 12 Pages |
Abstract
A protein discovered within inner mitochondrial membranes (IMM), designated as the mitochondrial ryanodine receptor (mRyR), has been recognized recently as a modulator of Ca2+ fluxes in mitochondria. The present study provides fundamental pharmacological and electrophysiological properties of this mRyR. Rat cardiac IMM fused to lipid bilayers revealed the presence of a mitochondrial channel with gating characteristics similar to those of classical sarcoplasmic reticulum RyR (SR-RyR), but a variety of other mitochondrial channels obstructed clean recordings. Mitochondrial vesicles were thus solubilized and subjected to sucrose sedimentation to obtain mRyR-enriched fractions. Reconstitution of sucrose-purified fractions into lipid bilayers yielded Cs+-conducting, Ca2+-sensitive, large conductance (500-800Â pS) channels with signature properties of SR-RyRs. Cytosolic Ca2+ increased the bursting frequency and mean open time of the channel. Micromolar concentrations of ryanodine induced the appearance of subconductance states or inhibited channel activity altogether, while Imperatoxin A (IpTxa), a specific activator of RyRs, reversibly induced the appearance of distinct subconductance states. Remarkably, the cardiac mRyR displayed a Ca2+ dependence of [3H]ryanodine binding curve similar to skeletal RyR (RyR1), not cardiac RyR (RyR2). Overall, the mRyR displayed elemental attributes that are present in single channel lipid bilayer recordings of SR-RyRs, although some exquisite differences were also noted. These results therefore provide the first direct evidence that a unique RyR occurs in mitochondrial membranes.
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Authors
Beth A. Altschafl, Gisela Beutner, Virendra K. Sharma, Shey-Shing Sheu, Héctor H. Valdivia,