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Luminal Ca2+ regulation of single cardiac ryanodine receptors: insights provided by calsequestrin and its mutants.

Qin J, Valle G, Nani A, Nori A, Rizzi N, Priori SG, Volpe P, Fill M - J. Gen. Physiol. (2008)

Bottom Line: It does not depend on CSQ2 oligomerization or CSQ2 monomer Ca2+ binding affinity.The R33Q CSQ2 mutant can participate in luminal RyR2 Ca2+ regulation but less effectively than wild-type (WT) CSQ2.CSQ2-L167H does not participate in luminal RyR2 Ca2+ regulation.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Physiology and Biophysics, Rush University Medical Center, Chicago, IL 60612, USA.

ABSTRACT
The luminal Ca2+ regulation of cardiac ryanodine receptor (RyR2) was explored at the single channel level. The luminal Ca2+ and Mg2+ sensitivity of single CSQ2-stripped and CSQ2-associated RyR2 channels was defined. Action of wild-type CSQ2 and of two mutant CSQ2s (R33Q and L167H) was also compared. Two luminal Ca2+ regulatory mechanism(s) were identified. One is a RyR2-resident mechanism that is CSQ2 independent and does not distinguish between luminal Ca2+ and Mg2+. This mechanism modulates the maximal efficacy of cytosolic Ca2+ activation. The second luminal Ca2+ regulatory mechanism is CSQ2 dependent and distinguishes between luminal Ca2+ and Mg2+. It does not depend on CSQ2 oligomerization or CSQ2 monomer Ca2+ binding affinity. The key Ca2+-sensitive step in this mechanism may be the Ca2+-dependent CSQ2 interaction with triadin. The CSQ2-dependent mechanism alters the cytosolic Ca2+ sensitivity of the channel. The R33Q CSQ2 mutant can participate in luminal RyR2 Ca2+ regulation but less effectively than wild-type (WT) CSQ2. CSQ2-L167H does not participate in luminal RyR2 Ca2+ regulation. The disparate actions of these two catecholaminergic polymorphic ventricular tachycardia (CPVT)-linked mutants implies that either alteration or elimination of CSQ2-dependent luminal RyR2 regulation can generate the CPVT phenotype. We propose that the RyR2-resident, CSQ2-independent luminal Ca2+ mechanism may assure that all channels respond robustly to large (>5 muM) local cytosolic Ca2+ stimuli, whereas the CSQ2-dependent mechanism may help close RyR2 channels after luminal Ca2+ falls below approximately 0.5 mM.

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Summary cartoon of RyR2 luminal Ca2+ regulation. Triadin is labeled TR. Calcium binding sites that activate channel are indicated with a plus. The cytosolic Ca2+ inhibitory site is marked with a minus. Proteins are not drawn to scale.
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fig7: Summary cartoon of RyR2 luminal Ca2+ regulation. Triadin is labeled TR. Calcium binding sites that activate channel are indicated with a plus. The cytosolic Ca2+ inhibitory site is marked with a minus. Proteins are not drawn to scale.

Mentions: Fig. 7 illustrates our overall working interpretation. In this cartoon, Ca2+ binding to the CSQ2 monomer and Ca2+-dependent CSQ2 oligomerization do not regulate the RyR2 channel. A CSQ2 monomer bound to the triadin–RyR2 complex is the key regulating entity. The Ca2+ sensitivity of CSQ2–triadin interaction is the key lumenal Ca2+ sensing step and it discriminates between Ca2+ and Mg2+. Lumenal Ca2+ alters the cytosolic Ca2+ sensitivity of the channel through the RyR2–triadin–CSQ2 interaction. There is also a RyR2-resident, CSQ2-independent, lumenal Ca2+ regulatory pathway that does not discriminate between Ca2+ and Mg2+.


Luminal Ca2+ regulation of single cardiac ryanodine receptors: insights provided by calsequestrin and its mutants.

Qin J, Valle G, Nani A, Nori A, Rizzi N, Priori SG, Volpe P, Fill M - J. Gen. Physiol. (2008)

Summary cartoon of RyR2 luminal Ca2+ regulation. Triadin is labeled TR. Calcium binding sites that activate channel are indicated with a plus. The cytosolic Ca2+ inhibitory site is marked with a minus. Proteins are not drawn to scale.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2279168&req=5

fig7: Summary cartoon of RyR2 luminal Ca2+ regulation. Triadin is labeled TR. Calcium binding sites that activate channel are indicated with a plus. The cytosolic Ca2+ inhibitory site is marked with a minus. Proteins are not drawn to scale.
Mentions: Fig. 7 illustrates our overall working interpretation. In this cartoon, Ca2+ binding to the CSQ2 monomer and Ca2+-dependent CSQ2 oligomerization do not regulate the RyR2 channel. A CSQ2 monomer bound to the triadin–RyR2 complex is the key regulating entity. The Ca2+ sensitivity of CSQ2–triadin interaction is the key lumenal Ca2+ sensing step and it discriminates between Ca2+ and Mg2+. Lumenal Ca2+ alters the cytosolic Ca2+ sensitivity of the channel through the RyR2–triadin–CSQ2 interaction. There is also a RyR2-resident, CSQ2-independent, lumenal Ca2+ regulatory pathway that does not discriminate between Ca2+ and Mg2+.

Bottom Line: It does not depend on CSQ2 oligomerization or CSQ2 monomer Ca2+ binding affinity.The R33Q CSQ2 mutant can participate in luminal RyR2 Ca2+ regulation but less effectively than wild-type (WT) CSQ2.CSQ2-L167H does not participate in luminal RyR2 Ca2+ regulation.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Physiology and Biophysics, Rush University Medical Center, Chicago, IL 60612, USA.

ABSTRACT
The luminal Ca2+ regulation of cardiac ryanodine receptor (RyR2) was explored at the single channel level. The luminal Ca2+ and Mg2+ sensitivity of single CSQ2-stripped and CSQ2-associated RyR2 channels was defined. Action of wild-type CSQ2 and of two mutant CSQ2s (R33Q and L167H) was also compared. Two luminal Ca2+ regulatory mechanism(s) were identified. One is a RyR2-resident mechanism that is CSQ2 independent and does not distinguish between luminal Ca2+ and Mg2+. This mechanism modulates the maximal efficacy of cytosolic Ca2+ activation. The second luminal Ca2+ regulatory mechanism is CSQ2 dependent and distinguishes between luminal Ca2+ and Mg2+. It does not depend on CSQ2 oligomerization or CSQ2 monomer Ca2+ binding affinity. The key Ca2+-sensitive step in this mechanism may be the Ca2+-dependent CSQ2 interaction with triadin. The CSQ2-dependent mechanism alters the cytosolic Ca2+ sensitivity of the channel. The R33Q CSQ2 mutant can participate in luminal RyR2 Ca2+ regulation but less effectively than wild-type (WT) CSQ2. CSQ2-L167H does not participate in luminal RyR2 Ca2+ regulation. The disparate actions of these two catecholaminergic polymorphic ventricular tachycardia (CPVT)-linked mutants implies that either alteration or elimination of CSQ2-dependent luminal RyR2 regulation can generate the CPVT phenotype. We propose that the RyR2-resident, CSQ2-independent luminal Ca2+ mechanism may assure that all channels respond robustly to large (>5 muM) local cytosolic Ca2+ stimuli, whereas the CSQ2-dependent mechanism may help close RyR2 channels after luminal Ca2+ falls below approximately 0.5 mM.

Show MeSH
Related in: MedlinePlus