title: RYR2 proteins contribute to the formation of Ca(2+) sparks in smooth muscle.
abstract: Calcium release through ryanodine receptors (RYR) activates calcium-dependent membrane conductances and plays an important role in excitation-contraction coupling in smooth muscle. The specific RYR isoforms associated with this release in smooth muscle, and the role of RYR-associated proteins such as FK506 binding proteins (FKBPs), has not been clearly established, however. FKBP12.6 proteins interact with RYR2 Ca(2+) release channels and the absence of these proteins predictably alters the amplitude and kinetics of RYR2 unitary Ca(2+) release events (Ca(2+) sparks). To evaluate the role of specific RYR2 and FBKP12.6 proteins in Ca(2+) release processes in smooth muscle, we compared spontaneous transient outward currents (STOCs), Ca(2+) sparks, Ca(2+)-induced Ca(2+) release, and Ca(2+) waves in smooth muscle cells freshly isolated from wild-type, FKBP12.6(-/-), and RYR3(-/-) mouse bladders. Consistent with a role of FKBP12.6 and RYR2 proteins in spontaneous Ca(2+) sparks, we show that the frequency, amplitude, and kinetics of spontaneous, transient outward currents (STOCs) and spontaneous Ca(2+) sparks are altered in FKBP12.6 deficient myocytes relative to wild-type and RYR3 null cells, which were not significantly different from each other. Ca(2+) -induced Ca(2+) release was similarly augmented in FKBP12.6(-/-), but not in RYR3 null cells relative to wild-type. Finally, Ca(2+) wave speed evoked by CICR was not different in RYR3 cells relative to control, indicating that these proteins are not necessary for normal Ca(2+) wave propagation. The effect of FKBP12.6 deletion on the frequency, amplitude, and kinetics of spontaneous and evoked Ca(2+) sparks in smooth muscle, and the finding of normal Ca(2+) sparks and CICR in RYR3 null mice, indicate that Ca(2+) release through RYR2 molecules contributes to the formation of spontaneous and evoked Ca(2+) sparks, and associated STOCs, in smooth muscle.
authors.affiliation: Department of Biomedical Sciences, Cornell University, Ithaca, NY 14853-6401, USA.
authors.forename: Guangju
authors.initials: G
authors.lastname: Ji
authors.forename: Morris E
authors.initials: ME
authors.lastname: Feldman
authors.forename: Kai Su
authors.initials: KS
authors.lastname: Greene
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Sorrentino
authors.forename: Hong-Bo
authors.initials: HB
authors.lastname: Xin
authors.forename: Michael I
authors.initials: MI
authors.lastname: Kotlikoff
mesh_terms: D000818:Animals; D020013:Calcium Signaling / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009130:Muscle, Smooth / Q000166:cytology / Q000502:physiology*; D032389:Myocytes, Smooth Muscle / Q000502:physiology; D018408:Patch-Clamp Techniques; D019837:Ryanodine Receptor Calcium Release Channel / Q000235:genetics / Q000378:metabolism*; D022021:Tacrolimus Binding Proteins / Q000235:genetics / Q000378:metabolism*; D001743:Urinary Bladder / Q000166:cytology / Q000502:physiology*
chemical_list: D019837:Ryanodine Receptor Calcium Release Channel; D022021:Tacrolimus Binding Proteins; C403484:tacrolimus binding protein 1B