Characterization of an inwardly rectifying chloride conductance expressed by cultured rat cortical astrocytes.
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.
Ferroni
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S
Dipartimento di Fisiologia umana e generale, Università di Bolgna, Italy. ferroni@biocfarm.unibo.it
Marchini
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C
Nobile
M
M
Rapisarda
C
C
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000494:pharmacology; D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D003994:Bucladesine / Q000494:pharmacology; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D018118:Chloride Channels / Q000187:drug effects / Q000378:metabolism*; D004594:Electrophysiology; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D051381:Rats
D018118:Chloride Channels; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D003994:Bucladesine; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid