Ferroni S, Marchini C, Nobile M, Rapisarda C
Dipartimento di Fisiologia umana e generale, Università di Bolgna, Italy.
Glia. 1997 Oct;21(2):217-27. doi: 10.1002/(sici)1098-1136(199710)21:2<217::aid-glia5>3.0.co;2-3.
The biophysical and pharmacological properties of the inwardly rectifying Cl- conductance (IClh), expressed in rat type-1 neocortical cultured astrocytes upon a long-term treatment (1-3 weeks) with dibutyryl-cyclic-AMP (dBcAMP), were investigated with the whole-cell patch-clamp technique. Using intra- and extra-cellular solutions with symmetrical high Cl- content and with the monovalent cations replaced with N-methyl-D-glucamine, time- and voltage-dependent Cl- currents were elicited in response to hyperpolarizing voltage steps from a holding potential of 0 mV. The inward currents activated slowly and did not display any time-dependent inactivation. The rising phase of the current traces was best fitted with two exponential components whose time constants decreased with larger hyperpolarization. The steady-state activation of IClh was well described by a single Boltzmann function with a half-maximal activation potential at - 62 mV and a slope of 19 mV that yields to an apparent gating charge of 1.3. The anion selectivity sequence was Cl- = Br- = I- > F- > cyclamate > or = gluconate. External application of the putative Cl- channel blockers 4,4 diisothiocyanatostilbene-2,2 disulphonic acid or 4-acetamido-4-isothiocyanatostilbene-2,2-disulphonic acid did not affect IClh. By contrast, anthracene-9-carboxylic acid, as well as Cd2+ and Zn2+, inhibited, albeit with different potencies, the Cl- current. Taken together, these results indicate that dBcAMP-treated cultured rat cortical astrocytes express a Cl- inward rectifier, which exhibits similar but not identical features compared with those of the cloned and heterologously expressed hyperpolarization-activated Cl- channel ClC-2.
运用全细胞膜片钳技术，研究了用二丁酰环磷腺苷（dBcAMP）长期处理（1 - 3周）的大鼠1型新皮质培养星形胶质细胞中内向整流性氯离子电导（IClh）的生物物理和药理学特性。使用细胞内和细胞外溶液，其中氯离子含量对称且单价阳离子被N - 甲基 - D - 葡糖胺取代，从0 mV的钳制电位进行超极化电压阶跃时，可引发时间和电压依赖性的氯离子电流。内向电流激活缓慢，且未表现出任何时间依赖性失活。电流轨迹的上升相最佳拟合为两个指数成分，其时间常数随更大的超极化而减小。IClh的稳态激活可用单一的玻尔兹曼函数很好地描述，其半最大激活电位为 - 62 mV，斜率为19 mV，表观门控电荷为1.3。阴离子选择性序列为Cl- = Br- = I- > F- > 环己基氨基磺酸盐 > 或 = 葡萄糖酸盐。外部施加假定的氯离子通道阻滞剂4,4 - 二异硫氰酸根合芪 - 2,2 - 二磺酸或4 - 乙酰氨基 - 4 - 异硫氰酸根合芪 - 2,2 - 二磺酸不影响IClh。相比之下，蒽 - 9 - 羧酸以及Cd2+和Zn2+虽效力不同，但均抑制氯离子电流。综上所述，这些结果表明，经dBcAMP处理的培养大鼠皮质星形胶质细胞表达一种氯离子内向整流器，与克隆并异源表达的超极化激活氯离子通道ClC - 2相比，它具有相似但不完全相同的特征。
