Saleh Sohag N, Angermann Jeff E, Sones William R, Leblanc Normand, Greenwood Iain A
Ion Channels and Cell Signaling Research Centre, Division of Basic Medical Sciences, St. George's, University of London, SW17 0RE London, UK.
J Pharmacol Exp Ther. 2007 Jun;321(3):1075-84. doi: 10.1124/jpet.106.118786. Epub 2007 Mar 8.
Because chloride (Cl(-)) channel blockers such as niflumic acid enhance large-conductance Ca(2+)-activated potassium channels (BK(Ca)), the aim of this study was to determine whether there is a reciprocal modification of Ca(2+)-activated chloride Cl(-) currents (I(ClCa)) by two selective activators of BK(Ca). Single smooth muscle cells were isolated by enzymatic digestion from murine portal vein and rabbit pulmonary artery. The BK(Ca) activators NS1619 [1,3-dihydro-1-[2-hydroxy-5-(trifluoromethyl-)phenyl]-5-(trifluoromethyl)-2H-benzimidazol-2-one] and isopimaric acid (IpA) augmented macroscopic I(ClCa) elicited by pipette solutions containing Ca(2+) > 100 nM without any alteration in current kinetics. Enhanced currents recorded in the presence of NS1619 or IpA reversed at the theoretical Cl(-) equilibrium potential, which was shifted by approximately -40 mV upon replacement of the external anion with the more permeable thiocyanate anion. NS1619 increased the sensitivity of calcium-activated chloride channel (Cl(Ca)) to Ca(2+) (approximately 100 nM at +60 mV) and induced a leftward shift in their voltage dependence (approximately 80 mV with 1 micro Ca(2+)). Single-channel experiments revealed that NS1619 increased the number of open channels times the open probability of small-conductance (1.8-3.1 pS) Cl(Ca) without any alteration in their unitary amplitude or number of observable unitary levels of activity. These data, in addition to the established stimulatory effects of niflumic acid on BK(Ca), show that there is similarity in the pharmacology of calcium-activated chloride and potassium channels. Although nonspecific interactions are possible, one alternative hypothesis is that the channel underlying vascular I(ClCa) shares some structural similarity to the BK(Ca) or that the latter K(+) channel physically interacts with Cl(Ca).
由于诸如氟尼酸之类的氯离子（Cl(-)）通道阻滞剂可增强大电导钙激活钾通道（BK(Ca)），本研究旨在确定BK(Ca)的两种选择性激活剂是否对钙激活氯离子电流（I(ClCa)）存在反向调节作用。通过酶消化从小鼠门静脉和兔肺动脉分离出单个平滑肌细胞。BK(Ca)激活剂NS1619 [1,3-二氢-1-[2-羟基-5-(三氟甲基)-苯基]-5-(三氟甲基)-2H-苯并咪唑-2-酮]和异海松酸（IpA）增强了由含有Ca(2+) > 100 nM的移液管溶液诱发的宏观I(ClCa)，且电流动力学无任何改变。在NS1619或IpA存在下记录到的增强电流在理论Cl(-)平衡电位处反转，当用更易通透的硫氰酸根阴离子替代外部阴离子时，该平衡电位大约偏移-40 mV。NS1619增加了钙激活氯离子通道（Cl(Ca)）对Ca(2+)的敏感性（在+60 mV时约为100 nM），并使其电压依赖性向左偏移（在1 μM Ca(2+)时约为80 mV）。单通道实验表明，NS1619增加了小电导（1.8 - 3.1 pS）Cl(Ca)的开放通道数量乘以开放概率，而其单通道幅度或可观察到的单通道活性水平数量均无任何改变。这些数据，除了已确定的氟尼酸对BK(Ca)的刺激作用外，还表明钙激活氯离子通道和钾通道在药理学上具有相似性。尽管可能存在非特异性相互作用，但另一种假设是，血管I(ClCa)所基于的通道与BK(Ca)具有某些结构相似性，或者后者的钾通道与Cl(Ca)存在物理相互作用。
