Ryanodine receptor type 2 deficiency changes excitation-contraction coupling and membrane potential in urinary bladder smooth muscle.
The possibility that the ryanodine receptor type 2 (RyR2) can function as the major Ca(2+)-induced Ca(2+) release (CICR) channel in excitation-contraction (E-C) coupling was examined in smooth muscle cells (SMCs) isolated from urinary bladder (UB) of RyR2 heterozygous KO mice (RyR2+/-). RyR2 mRNA expression in UB from RyR2+/- was much lower than that in wild-type (RyR2+/+. In single UBSMCs from RyR2+/+, membrane depolarization under voltage clamp initially induced several local Ca(2+) transients (hot spots) in peripheral areas of the cell. Then, Ca(2+) waves spread from Ca(2+) hot spots to other areas of the myocyte. The number of Ca(2+) hot spots elicited by a short depolarization (< 20 ms) in UBSMCs of RyR2+/- was significantly smaller than in those of RyR2+/+. The force development induced either by direct electrical stimulation or by 10 microm acetylcholine in tissue segments of RyR2+/- was smaller than and comparable to those in RyR2+/+, respectively. The frequency of spontaneous transient outward currents in single myocytes and the membrane depolarization by 1 microm paxilline in tissue segments from RyR2+/- were significantly lower and smaller than those in RyR2+/+, respectively. The urination frequency and volume per voiding in RyR2+/- were significantly increased and reduced, respectively, compared with RyR2+/+. In conclusion, RyR2 plays a crucial role in the regulation of CICR during E-C coupling and also in the regulation of resting membrane potential, presumably via the modulation of Ca(2+)-dependent K(+) channel activity in UBSMCs and, thereby, has a pivotal role in the control of bladder activity.
Hotta
Shingo
S
Department of Molecular and Cellular Pharmacology, Graduate School of Pharmaceutical Science, Nagoya City University, 3-1 Tanabedori, Mizuhoku, Nagoya 467-8603, Japan.
Morimura
Kozo
K
Ohya
Susumu
S
Muraki
Katsuhiko
K
Takeshima
Hiroshi
H
Imaizumi
Yuji
Y
D000818:Animals; D001692:Biological Transport / Q000235:genetics; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling; D004594:Electrophysiology; D005838:Genotype; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials; D051379:Mice; D018345:Mice, Knockout / Q000235:genetics; D009119:Muscle Contraction / Q000502:physiology*; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D018408:Patch-Clamp Techniques; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000378:metabolism; D019837:Ryanodine Receptor Calcium Release Channel / Q000172:deficiency* / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D013347:Subcellular Fractions / Q000378:metabolism; D001743:Urinary Bladder / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D014554:Urination / Q000502:physiology
D012333:RNA, Messenger; D019837:Ryanodine Receptor Calcium Release Channel; D002110:Caffeine; D002118:Calcium