Article

The mitochondrial ryanodine receptor in rat heart: a pharmaco-kinetic profile.

Department of Physiology, University of Wisconsin Medical School, 601 Science Drive, Madison, WI 53711, USA.
Biochimica et Biophysica Acta (impact factor: 4.66). 08/2007; 1768(7):1784-95. DOI:10.1016/j.bbamem.2007.04.011 pp.1784-95
Source: PubMed

ABSTRACT A protein discovered within inner mitochondrial membranes (IMM), designated as the mitochondrial ryanodine receptor (mRyR), has been recognized recently as a modulator of Ca(2+) 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, Ca(2+)-sensitive, large conductance (500-800 pS) channels with signature properties of SR-RyRs. Cytosolic Ca(2+) 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 (IpTx(a)), a specific activator of RyRs, reversibly induced the appearance of distinct subconductance states. Remarkably, the cardiac mRyR displayed a Ca(2+) dependence of [(3)H]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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Keywords

[(3)H]ryanodine binding curve
 
bursting frequency
 
cardiac mRyR
 
classical sarcoplasmic reticulum RyR
 
distinct subconductance states
 
elemental attributes
 
first direct evidence
 
inhibited channel activity
 
inner mitochondrial membranes
 
large conductance
 
lipid bilayers
 
mitochondrial channel
 
mitochondrial channels
 
mitochondrial membranes
 
mitochondrial ryanodine receptor
 
mRyR-enriched fractions
 
single channel lipid bilayer recordings
 
skeletal RyR
 
SR-RyRs
 
subconductance states