The mitochondrial ryanodine receptor in rat heart: a pharmaco-kinetic profile.
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.
Altschafl
Beth A
BA
Department of Physiology, University of Wisconsin Medical School, 601 Science Drive, Madison, WI 53711, USA.
Beutner
Gisela
G
Sharma
Virendra K
VK
Sheu
Shey-Shing
SS
Valdivia
Héctor H
HH
D000818:Animals; D001001:Anura; D002118:Calcium / Q000502:physiology; D002458:Cell Fractionation; D002499:Centrifugation, Density Gradient; D008051:Lipid Bilayers / Q000378:metabolism*; D008929:Mitochondria, Heart / Q000737:chemistry; D051336:Mitochondrial Membranes / Q000378:metabolism*; D051381:Rats; D012433:Ryanodine / Q000493:pharmacokinetics / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel / Q000187:drug effects / Q000502:physiology*; D012519:Sarcoplasmic Reticulum / Q000737:chemistry; D012604:Scorpion Venoms / Q000494:pharmacology; D013385:Succinate Dehydrogenase / Q000032:analysis
D008051:Lipid Bilayers; D019837:Ryanodine Receptor Calcium Release Channel; D012604:Scorpion Venoms; C105361:imperatoxin A; D012433:Ryanodine; D013385:Succinate Dehydrogenase; D002118:Calcium