RyR1-specific requirement for depolarization-induced Ca2+ sparks in urinary bladder smooth muscle
Nicolas Fritz1, Jean-Luc Morel, Loice H Jeyakumar
1CNRS UMR 5017, Laboratoire de Signalisation et Interactions Cellulaires, Université Bordeaux 2, Bordeaux, France.
Abstract:
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.
Insights
Ryanodine receptor subtype 1 (RyR1) is essential for calcium (Ca2+) sparks in urinary bladder smooth muscle. Its absence leads to altered Ca2+ signaling and waves, highlighting RyR1
Area of Science:
- Physiology
- Molecular Biology
- Smooth Muscle Research
Background:
- Ryanodine receptor subtype 1 (RyR1) is mainly studied in skeletal muscle, but its role in smooth muscle, particularly the urinary bladder, is less understood.
- Calcium (Ca2+) signaling is critical for smooth muscle function, and ryanodine receptors are key regulators of intracellular Ca2+ release.
Purpose of the Study:
- To investigate the specific role of RyR1 in Ca2+ signaling within urinary bladder smooth muscle using Ryr1-null mice.
- To elucidate the contribution of RyR1 to depolarization-induced Ca2+ sparks and overall Ca2+ dynamics in this tissue.
Main Methods:
- Utilized Ryr1-null mice to examine Ca2+ signaling in isolated urinary bladder smooth muscle cells.
- Employed immunostaining to determine the subcellular localization of RyR isoforms (RyR1, RyR2, RyR3).
- Analyzed protein expression levels of RyR-associated proteins, specifically FKBP12 and FKBP12.6.
- Investigated the effects of rapamycin, an FKBP uncoupler, on RyR-dependent Ca2+ signaling.
Main Results:
- RyR1 is indispensable for depolarization-induced Ca2+ sparks in urinary bladder myocytes; RyR2 and RyR3 mediate other Ca2+ events.
- RyR1 localizes to the superficial sarcoplasmic reticulum, while RyR2 and RyR3 are found in the deep sarcoplasmic reticulum.
- Ryr1-null myocytes exhibit reduced FKBP12 and FKBP12.6 levels, increased spontaneous Ca2+ waves, and loss of depolarization-induced sparks.
- Rapamycin enhances RyR-dependent Ca2+ signaling in wild-type but not Ryr1-null myocytes, confirming FKBP involvement.
Conclusions:
- RyR1 is critically required for depolarization-induced Ca2+ sparks in urinary bladder smooth muscle.
- The subcellular localization of RyR1 plays a crucial role in fine-tuning Ca2+ signals in smooth muscle.
- Downregulation of FKBP proteins in Ryr1-null myocytes contributes to altered Ca2+ signaling patterns.
Related Concept Videos
01:25Smooth Muscle Contraction
The onset of contraction is triggered by an increase in calcium ions within the sarcoplasm, similar to the process in striated muscle. However, smooth muscles have a relatively smaller reservoir of the sarcoplasmic...
01:29Relaxation of Skeletal Muscles
When an action potential reaches the axon terminal, it depolarizes the membrane and opens voltage-gated sodium channels. Sodium ions enter the cell, further depolarizing the presynaptic membrane. This depolarization causes voltage-gated calcium channels to open.