OBJECTIVE To investigate the changes in spontaneous bladder smooth muscle contractions that occur during detrusor instability (DI), and to test the possibility that altered function or expression of ryanodine receptors (RyRs) could account for the increased bladder contractions. MATERIALS AND METHODS After 8 weeks of partial bladder outlet obstruction, DI was confirmed in female experimental rats by filling cystometry. Muscle strips were dissected from freshly isolated bladders, and isometric tension recorded in strips from DI and normal bladders. The contractions were recorded during electrical stimulation or exposure to various agents. Western blot analysis was used to determine RyR expression in DI and normal bladder muscle. RESULTS In DI bladder muscle, spontaneous contractile activity persisted in the presence of blockers for known neurotransmitter receptors in the bladder wall. The RyR blocker ryanodine significantly increased the spontaneous contractile frequency in normal bladder strips, but failed to affect spontaneous contractions in DI muscle. Caffeine inhibited spontaneous contractile activity in both the DI and normal strips. After administering the L-type Ca 2+channel antagonist nimodipine, the myogenic contractile activity was abolished in normal strips; in contrast, in DI strips, the amplitude of contractions was reduced but the frequency of contractions was unchanged. Western blot analysis showed that RyR expression was lower in DI muscle than in normal bladder muscle. CONCLUSION These results provide the first characterization of a loss of regulation of spontaneous contractile activity by RyRs in DI muscle associated with a significant decrease in RyR expression. RyRs in normal detrusor muscle act as negative-feedback regulators of spontaneous contractile activity, presumably by releasing Ca 2+that activates Ca 2+-dependent K + channels to decrease contractility. This mechanism might be weakened in DI muscle, resulting in spontaneous contractile overactivity.

目的探讨周期性张力作用下的逼尿肌细胞表型转化与其生物力学特性改变的关系。方法在特殊的培养皿上分离培养Wistar大鼠膀胱逼尿肌细胞，对其施加周期性牵拉后，分别采用免疫荧光、氚标胸腺嘧啶核苷掺入实验、流式细胞仪等测定逼尿肌细胞表型标志如SM-a-actin、细胞增殖状况等，评价逼尿肌细胞的表型转化状况；利用图像采集及分析系统、微管吸吮技术分别测定单个逼尿肌细胞收缩力及黏弹性，反映张力条件下其生物力学特性的改变。 结果未施加张力组与实验组之间差异显著；周期性牵拉导！致逼尿肌细胞出现由“收缩型”向“合成型”的表型转化，总体上表现为actin表达降低且排列趋于紊乱、细胞增殖活跃；功能上出现单细胞收缩力减弱、黏弹性下降。结论对培养逼尿肌细胞施加周期性张力负荷作用是在细胞水平模拟膀胱出口梗阻的有效方法；逼尿肌细胞表型转化正是其生物力学特性发生改变的结构基础。

目的探讨M受体亚型与逼尿肌功能变化之间的关系。方法于平面横断人鼠脊髓，3周后行膀胱压力容积测定和体外肌条拉力试验。结果实验组为低顺应性和不稳定膀胱，在一定张力下逼尿肌有自发性收缩产生。实验组体外肌条自发性收缩频率(4.797±0.257次/min)及收缩力较对照组（3.227±0.173次/min）升高。阿托品（4.846±0.187次/min）、4DAMP（4.696±0.247次/min）和mcthoctramin（4.719±0.200次/min）对肌条自发性收缩频率无影响。卡巴可能使自发性收缩频率(6.316±0.409次/min)和收缩力增加，阿托品（5.304±0.095次/min）和4DAMP（5.046±0.089次/min）可部分抑制这种作用，mcthoctramin（6.684±0.077次/min）作用不明显。结论逼尿肌自律性不依赖M受体及其亚型，肌源性因素是逼尿肌反射亢进产生的重要原因。M3受体亚型能进一步增加逼尿肌自律性和收缩力。