Bradley E, Hollywood M A, Johnston L, Large R J, Matsuda T, Baba A, McHale N G, Thornbury K D, Sergeant Gerard P
Smooth Muscle Research Centre, Regional Development Centre, Dundalk Institute of Technology, Dundalk, Co. Louth, Ireland.
J Physiol. 2006 Aug 1;574(Pt 3):651-61. doi: 10.1113/jphysiol.2006.110932. Epub 2006 May 25.
Interstitial cells of Cajal (ICC) isolated from the rabbit urethra exhibit regular Ca2+ oscillations that are associated with spontaneous transient inward currents (STICs) recorded under voltage clamp. Their frequency is known to be very sensitive to external Ca2+ concentration but the mechanism of this has yet to be elucidated. In the present study experiments were performed to assess the role of Na+-Ca2+ exchange (NCX) in this process. Membrane currents were recorded using the patch clamp technique and measurements of intracellular Ca2+ were made using fast confocal microscopy. When reverse mode NCX was enhanced by decreasing the external Na+ concentration [Na+]o from 130 to 13 mM, the frequency of global Ca2+ oscillations and STICs increased. Conversely, inhibition of reverse mode NCX by KB-R7943 and SEA0400 decreased the frequency of Ca2+ oscillations and STICs. Application of caffeine (10 mM) and noradrenaline (10 microM) induced transient Ca2+-activated chloride currents (I(ClCa)) at -60 mV due to release of Ca2+ from ryanodine- and inositol trisphosphate (IP3)-sensitive Ca2+ stores, respectively, but these responses were not blocked by KB-R7943 or SEA0400 suggesting that neither drug blocked Ca2+-activated chloride channels or Ca2+ release from stores. Intact strips of rabbit urethra smooth muscle develop spontaneous myogenic tone. This tone was relaxed by application of SEA0400 in a concentration-dependent fashion. Finally, single cell RT-PCR experiments revealed that isolated ICC from the rabbit urethra only express the type 3 isoform of the Na+-Ca2+ exchanger (NCX3). These results suggest that frequency of spontaneous activity in urethral ICC can be modulated by Ca2+ entry via reverse NCX.
从兔尿道分离出的Cajal间质细胞（ICC）呈现出规则的Ca2+振荡，这与电压钳记录下的自发瞬态内向电流（STICs）相关。已知其频率对细胞外Ca2+浓度非常敏感，但其机制尚待阐明。在本研究中，进行了实验以评估钠钙交换体（NCX）在此过程中的作用。使用膜片钳技术记录膜电流，并使用快速共聚焦显微镜测量细胞内Ca2+。当通过将细胞外Na+浓度[Na+]o从130 mM降至13 mM来增强反向模式NCX时全局Ca2+振荡和STICs的频率增加。相反，KB-R7943和SEA0400对反向模式NCX的抑制降低了Ca2+振荡和STICs的频率。施加咖啡因（10 mM）和去甲肾上腺素（10 microM）分别由于从兰尼碱和三磷酸肌醇（IP3）敏感的Ca2+储存库中释放Ca2+而在-60 mV处诱导了瞬时Ca2+激活的氯电流（I(ClCa)），但这些反应未被KB-R7943或SEA0400阻断，这表明两种药物均未阻断Ca2+激活的氯通道或从储存库中释放Ca2+。完整的兔尿道平滑肌条会产生自发的肌源性张力。SEA0400以浓度依赖的方式松弛了这种张力。最后，单细胞逆转录-聚合酶链反应（RT-PCR）实验表明，从兔尿道分离出的ICC仅表达钠钙交换体（NCX）的3型异构体（NCX3）。这些结果表明，尿道ICC中自发活动的频率可通过反向NCX介导的Ca2+内流进行调节。
