Smith R D, Borisova L, Wray Susan, Burdyga T
The Physiological laboratory, University of Liverpool, Crown Street, Liverpool L69 3BX, UK.
Pflugers Arch. 2002 Dec;445(3):444-53. doi: 10.1007/s00424-002-0941-7. Epub 2002 Sep 28.
To better understand excitability, and hence contraction, the ionic currents underlying the action potential were identified and characterised in enzymatically isolated smooth muscle cells of the rat ureter. Using the whole-cell patch-clamp, under voltage-clamp conditions with K(+) in the pipette, three types of responses occurred to depolarisation: (1) sustained outward current and spontaneous transient outward currents (STOCs); (2) inward current; and (3) fast outward current. Investigation using different voltage protocols and pharmacological blockers and agonists revealed the presence of three outward and two inward currents. The outward currents were: (1) a sustained BK current, sensitive to low concentrations of tetraethylammonium (TEA) and featuring bursts of STOCs superimposed on it; (2) a fast, transient, A-type K current sensitive to 4-aminopyridine; and (3) a TEA and Ca(2+)-insensitive, late K(+) rectifier current. The inward currents were: (1) a fast L-type Ca(2+) channel current sensitive to nifedipine, Cd(2+) and potentiated by Ba(2+); and (2) a Ca(2+)-sensitive Cl(-) channel, which was inhibited by niflumic acid and Ba(2+), and produced a large tail current upon repolarisation at the end of the voltage step. The I- V relationships and peak amplitudes of all the currents are described. The finding of a K(+) rectifier and Ca(2+)-activated Cl(-) channel distinguish the rat ureteric cells from those of the guinea-pig. Thus, as well as the previously established difference in sarcoplasmic reticulum Ca(2+)-release mechanisms, there is also a species difference in ion channel expression in this tissue. We relate these currents to their possible contribution to the characteristically extremely long lasting action potential in the rat ureter.
为了更好地理解兴奋性，进而理解收缩过程，研究人员对大鼠输尿管酶解分离的平滑肌细胞中动作电位的离子电流进行了识别和表征。使用全细胞膜片钳技术，在移液管中含有K(+)的电压钳条件下，去极化会引发三种类型的反应：(1) 持续外向电流和自发瞬时外向电流（STOCs）；(2) 内向电流；(3) 快速外向电流。通过使用不同的电压方案以及药理学阻断剂和激动剂进行研究，发现存在三种外向电流和两种内向电流。外向电流包括：(1) 一种持续的BK电流，对低浓度的四乙铵（TEA）敏感，且其上叠加有STOCs爆发；(2) 一种对4-氨基吡啶敏感的快速、瞬时的A型K电流；(3) 一种对TEA和Ca(2+)不敏感的晚期K(+)整流电流。内向电流包括：(1) 一种对硝苯地平、Cd(2+)敏感且被Ba(2+)增强的快速L型Ca(2+)通道电流；(2) 一种Ca(2+)敏感的Cl(-)通道，被氟尼酸和Ba(2+)抑制，并且在电压阶跃结束复极化时产生大的尾电流。文中描述了所有电流的I-V关系和峰值幅度。K(+)整流器和Ca(2+)激活的Cl(-)通道的发现使大鼠输尿管细胞与豚鼠输尿管细胞区分开来。因此，除了先前确定的肌浆网Ca(2+)释放机制的差异外，该组织中离子通道表达也存在种属差异。我们将这些电流与其对大鼠输尿管中典型的极长时程动作电位的可能贡献联系起来。
