Fry C H, Sui G, Wu C
Institute of Urology, University College London, London W1W 7EY, UK.
Cell Calcium. 2006 Aug;40(2):231-9. doi: 10.1016/j.ceca.2006.04.027. Epub 2006 Jun 23.
T-type Ca2+ current has been recorded in smooth muscle myocytes, and associated interstitial cells, isolated from the gastro-intestinal tract, urinary bladder, urethra, prostate gland, myometrium, vas deferens, lymphatic vessels and airways smooth muscle. By contrast, current through such channels has not been recorded from other tissues, such as the ureter. Whilst the properties of this Ca2+ current are similar in most of these cells, with respect to their voltage-dependence, ion selectivity and response to channel modulators, some differences have been recorded, most notably in the gastro-intestinal tract, and may demand a reappraisal of how a T-type Ca2+ current is characterised. The functions of such a current in different tissues remains uncertain. In most of smooth muscles discussed in this review, it is hypothesised that it underlies rhythmic or spontaneous electrical activity, especially in concert with other current-carrying systems, such as Ca2+-activated outward currents. Of equal interest is that the T-type Ca2+ channel may be a target for agents that modulate tissue function, especially in pathological conditions, or are the site of secondary effects of agents used in clinical medicine. For example, T-type Ca2+ channel modulators have been proposed to reduce overactive muscular activity in the gastro-intestinal or urinary tract, or function as tocolytic agents: and the action of volatile anaesthetics on them in airways smooth muscle requires consideration in their overall action.
T型钙电流已在从胃肠道、膀胱、尿道、前列腺、子宫肌层、输精管、淋巴管及气道平滑肌中分离出的平滑肌细胞及相关间质细胞中记录到。相比之下，尚未在输尿管等其他组织中记录到通过此类通道的电流。虽然在大多数这些细胞中，这种钙电流的特性在电压依赖性、离子选择性及对通道调节剂的反应方面相似，但也记录到了一些差异，最显著的是在胃肠道，这可能需要重新评估如何对T型钙电流进行表征。这种电流在不同组织中的功能仍不确定。在本综述讨论的大多数平滑肌中，据推测它是节律性或自发性电活动的基础，尤其是与其他载流系统协同作用时，如钙激活外向电流。同样有趣的是，T型钙通道可能是调节组织功能的药物的作用靶点，尤其是在病理状态下，或者是临床医学中所用药物的次要作用位点。例如，已有人提出T型钙通道调节剂可减少胃肠道或泌尿道的过度活跃肌肉活动，或用作宫缩抑制剂：挥发性麻醉剂对气道平滑肌中T型钙通道的作用需要在其整体作用中加以考虑。
