Centre for Urology Research, Faculty of Health Sciences and Medicine, Bond University, Gold Coast, Queensland, Australia.
Am J Physiol Cell Physiol. 2023 Mar 1;324(3):C787-C797. doi: 10.1152/ajpcell.00441.2022. Epub 2023 Jan 23.
The influence of extracellular and intracellular calcium on smooth muscle contractile activity varies between organs. In response to G protein-coupled receptor (GPCR) stimulation, the urinary bladder detrusor muscle has shown a 70% dependence on extracellular calcium, whereas the urothelium and lamina propria (U&LP) has a 20%-50% dependence. However, as this only accounts for partial contractile activity, the contribution of intracellular calcium and calcium sensitization pathways remains unclear. This study assessed the role of intracellular signaling pathways on GPCR-mediated urinary bladder U&LP contraction. Porcine U&LP responses to activation of the G-coupled muscarinic, histamine, 5-hydroxytryptamine (serotonin), neurokinin, prostaglandin, and angiotensin II receptors were assessed with three selective inhibitors of store-released intracellular calcium, 2-aminoethyl diphenylborinate (2-APB), cyclopiazonic acid (CPA), and ruthenium red, and three Rho kinase inhibitors, fasudil, Y-27632, and GSK269962. There was no discernible impact on receptor agonist-induced contractions of the U&LP after blocking intracellular calcium pathways, suggesting that this tissue is more sensitive to alterations in the availability of extracellular calcium. However, an alternative mechanism of action for GPCR-mediated contraction was identified to be the activation of Rho kinase, such as when Y-27632 significantly reduced the GPCR-mediated contractile activity of the U&LP by approximately 50% ( < 0.05, = 8). This suggests that contractile responses of the bladder U&LP do not involve a significant release of calcium from intracellular stores, but that G-coupled receptor activation causes calcium sensitization via Rho kinase. This study highlights a key role for Rho kinase in the urinary bladder, which may provide a novel target in the future pharmaceutical management of bladder contractile disorders.
细胞外和细胞内钙对平滑肌收缩活性的影响因器官而异。在响应 G 蛋白偶联受体 (GPCR) 刺激时，膀胱逼尿肌显示出对细胞外钙的 70%依赖性，而尿路上皮和固有层 (U&LP) 则有 20%-50%的依赖性。然而，由于这仅占部分收缩活性，细胞内钙和钙敏化途径的贡献仍不清楚。本研究评估了细胞内信号通路在 GPCR 介导的膀胱 U&LP 收缩中的作用。通过三种选择性的细胞内钙释放抑制剂 2-氨基乙基二苯基硼酸 (2-APB)、环匹阿尼酸 (CPA) 和钌红，以及三种 Rho 激酶抑制剂法舒地尔、Y-27632 和 GSK269962，评估了猪 U&LP 对 G 偶联毒蕈碱、组胺、5-羟色胺 (血清素)、神经激肽、前列腺素和血管紧张素 II 受体激活的反应。阻断细胞内钙通路后，对受体激动剂诱导的 U&LP 收缩没有明显影响，这表明该组织对细胞外钙可用性的变化更为敏感。然而，已经确定 GPCR 介导的收缩的另一种作用机制是 Rho 激酶的激活，例如，当 Y-27632 显著降低 U&LP 的 GPCR 介导的收缩活性约 50%（<0.05，n=8）时。这表明膀胱 U&LP 的收缩反应不涉及细胞内储存库中钙的大量释放，而是 G 偶联受体激活通过 Rho 激酶引起钙敏化。本研究强调了 Rho 激酶在膀胱中的关键作用，这可能为未来膀胱收缩障碍的药物治疗提供新的靶点。
