Hotta Shingo, Morimura Kozo, Ohya Susumu, Muraki Katsuhiko, Takeshima Hiroshi, Imaizumi Yuji
Department of Molecular and Cellular Pharmacology, Graduate School of Pharmaceutical Science, Nagoya City University, 3-1 Tanabedori, Mizuhoku, Nagoya 467-8603, Japan.
J Physiol. 2007 Jul 15;582(Pt 2):489-506. doi: 10.1113/jphysiol.2007.130302. Epub 2007 Mar 15.
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.
在从兰尼碱受体2（RyR2）杂合敲除小鼠（RyR2+/-）膀胱（UB）分离的平滑肌细胞（SMC）中，研究了RyR2作为兴奋-收缩（E-C）偶联中主要的钙诱导钙释放（CICR）通道的可能性。RyR2+/-小鼠UB中RyR2 mRNA表达远低于野生型（RyR2+/+）。在来自RyR2+/+的单个UB SMC中，电压钳下的膜去极化最初在细胞周边区域诱导了几个局部钙瞬变（热点）。然后，钙波从钙热点扩散到心肌细胞的其他区域。RyR2+/-的UB SMC中短时间去极化（<20毫秒）引发的钙热点数量明显少于RyR2+/+。RyR2+/-组织片段中直接电刺激或10微摩尔乙酰胆碱诱导的力发展分别小于和相当于RyR2+/+。RyR2+/-单个心肌细胞中自发瞬时外向电流的频率以及组织片段中1微摩尔帕吉林引起的膜去极化分别明显低于和小于RyR2+/+。与RyR2+/+相比，RyR2+/-的排尿频率明显增加，每次排尿量明显减少。总之，RyR2在E-C偶联期间CICR的调节中以及在静息膜电位的调节中起关键作用，可能是通过调节UB SMC中钙依赖性钾通道活性，从而在膀胱活动控制中起关键作用。
