RyR1-specific requirement for depolarization-induced Ca2+ sparks in urinary bladder smooth muscle

J Cell Sci. 2007 Nov 1;120(Pt 21):3784-91. doi: 10.1242/jcs.009415. Epub 2007 Oct 9.


Ryanodine receptor subtype 1 (RyR1) has been primarily characterized in skeletal muscle but several studies have revealed its expression in smooth muscle. Here, we used Ryr1-null mice to investigate the role of this isoform in Ca(2+) signaling in urinary bladder smooth muscle. We show that RyR1 is required for depolarization-induced Ca(2+) sparks, whereas RyR2 and RyR3 are sufficient for spontaneous or caffeine-induced Ca(2+) sparks. Immunostaining revealed specific subcellular localization of RyR1 in the superficial sarcoplasmic reticulum; by contrast, RyR2 and RyR3 are mainly expressed in the deep sarcoplasmic reticulum. Paradoxically, lack of depolarization-induced Ca(2+) sparks in Ryr1(-/-) myocytes was accompanied by an increased number of cells displaying spontaneous or depolarization-induced Ca(2+) waves. Investigation of protein expression showed that FK506-binding protein (FKBP) 12 and FKBP12.6 (both of which are RyR-associated proteins) are downregulated in Ryr1(-/-) myocytes, whereas expression of RyR2 and RyR3 are unchanged. Moreover, treatment with rapamycin, which uncouples FKBPs from RyR, led to an increase of RyR-dependent Ca(2+) signaling in wild-type urinary bladder myocytes but not in Ryr1(-/-) myocytes. In conclusion, although decreased amounts of FKBP increase Ca(2+) signals in Ryr1(-/-) urinary bladder myocytes the depolarization-induced Ca(2+) sparks are specifically lost, demonstrating that RyR1 is required for depolarization-induced Ca(2+) sparks and suggesting that the intracellular localization of RyR1 fine-tunes Ca(2+) signals in smooth muscle.

Publication types

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

MeSH terms

  • Animals
  • Antibiotics, Antineoplastic / metabolism
  • Caffeine / metabolism
  • Calcium / metabolism*
  • Calcium Signaling / physiology*
  • Cells, Cultured
  • Central Nervous System Stimulants / metabolism
  • Membrane Potentials / physiology
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Mice, Transgenic
  • Muscle, Smooth / metabolism*
  • Myocytes, Smooth Muscle / cytology
  • Myocytes, Smooth Muscle / metabolism*
  • Ryanodine Receptor Calcium Release Channel / genetics
  • Ryanodine Receptor Calcium Release Channel / metabolism*
  • Sirolimus / metabolism
  • Tacrolimus Binding Protein 1A / genetics
  • Tacrolimus Binding Protein 1A / metabolism
  • Urinary Bladder / anatomy & histology*
  • Urinary Bladder / metabolism


  • Antibiotics, Antineoplastic
  • Central Nervous System Stimulants
  • Ryanodine Receptor Calcium Release Channel
  • Caffeine
  • Tacrolimus Binding Protein 1A
  • Calcium
  • Sirolimus