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

J Gen Physiol. 2008 Apr;131(4):325-34. doi: 10.1085/jgp.200709907. Epub 2008 Mar 17.


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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Substitution
  • Animals
  • Calcium / chemistry*
  • Calcium / metabolism
  • Calcium Signaling
  • Calsequestrin / chemistry
  • Calsequestrin / metabolism*
  • Cytosol / chemistry
  • Cytosol / metabolism
  • Dimerization
  • Electric Conductivity
  • Ion Channel Gating / physiology
  • Lipid Bilayers
  • Magnesium / chemistry
  • Magnesium / metabolism
  • Microsomes
  • Mutant Proteins / chemistry
  • Mutant Proteins / metabolism*
  • Myocytes, Cardiac / metabolism*
  • Patch-Clamp Techniques
  • Rats
  • Ryanodine Receptor Calcium Release Channel / chemistry*
  • Ryanodine Receptor Calcium Release Channel / metabolism
  • Sarcoplasmic Reticulum / metabolism
  • Structure-Activity Relationship
  • Tachycardia, Ventricular / etiology
  • Tachycardia, Ventricular / physiopathology


  • Calsequestrin
  • Lipid Bilayers
  • Mutant Proteins
  • Ryanodine Receptor Calcium Release Channel
  • Magnesium
  • Calcium