RyR1-specific requirement for depolarization-induced Ca2+ sparks in urinary bladder smooth muscle.
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.
Fritz
Nicolas
N
CNRS UMR 5017, Laboratoire de Signalisation et Interactions Cellulaires, Université Bordeaux 2, Bordeaux, France.
Morel
Jean-Luc
JL
Jeyakumar
Loice H
LH
Fleischer
Sidney
S
Allen
Paul D
PD
Mironneau
Jean
J
Macrez
Nathalie
N
D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000378:metabolism; D002110:Caffeine / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D002478:Cells, Cultured; D000697:Central Nervous System Stimulants / Q000378:metabolism; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D009130:Muscle, Smooth / Q000378:metabolism*; D032389:Myocytes, Smooth Muscle / Q000166:cytology / Q000378:metabolism*; D019837:Ryanodine Receptor Calcium Release Channel / Q000235:genetics / Q000378:metabolism*; D020123:Sirolimus / Q000378:metabolism; D022061:Tacrolimus Binding Protein 1A / Q000235:genetics / Q000378:metabolism; D001743:Urinary Bladder / Q000033:anatomy & histology* / Q000378:metabolism
D000903:Antibiotics, Antineoplastic; D000697:Central Nervous System Stimulants; D019837:Ryanodine Receptor Calcium Release Channel; D002110:Caffeine; D022061:Tacrolimus Binding Protein 1A; D002118:Calcium; D020123:Sirolimus