Characterization of an inwardly rectifying chloride conductance expressed by cultured rat cortical astrocytes

✍ Scribed by Stefano Ferroni; Cristina Marchini; Mario Nobile; Carmela Rapisarda

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 205 KB
• Volume: 21
• Category: Article
• ISSN: 0894-1491
• DOI: 10.1002/(sici)1098-1136(199710)21:2<217::aid-glia5>3.0.co;2-3

✦ Synopsis

The biophysical and pharmacological properties of the inwardly rectifying Cl Ϫ conductance (I Clh ), 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 Ϫ content and with the monovalent cations replaced with N-methyl-D-glucamine, time-and voltage-dependent Cl Ϫ 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 I Clh was well described by a single Boltzmann function with a half-maximal activation potential at Ϫ62 mV and a slope of 19 mV that yields to an apparent gating charge of 1.3. The anion selectivity sequence was Cl Ϫ ϭ Br Ϫ ϭ I Ϫ Ͼ F Ϫ Ͼ cyclamate Ն gluconate. External application of the putative Cl Ϫ channel blockers 4,4 diisothiocyanatostilbene-2,2 disulphonic acid or 4-acetamido-4-isothiocyanatostilbene-2,2-disulphonic acid did not affect I Clh . By contrast, anthracene-9-carboxylic acid, as well as Cd 2ϩ and Zn 2ϩ , inhibited, albeit with different potencies, the Cl Ϫ current. Taken together, these results indicate that dBcAMP-treated cultured rat cortical astrocytes express a Cl Ϫ inward rectifier, which exhibits similar but not identical features compared with those of the cloned and heterologously expressed hyperpolarization-activated Cl Ϫ channel ClC-2.