Biophysical and pharmacological characterization of chloride currents in human astrocytoma cells.
Expression of voltage-activated ion channels was studied in primary cultures from seven freshly resected human primary brain tumors and in an established human astrocytoma cell line, STTG1. Astrocytoma cells consistently expressed voltage-dependent outwardly rectifying currents. Currents activated at potentials > 45 mV and showed outward transients on termination of voltage steps. Currents reversed at the Cl equilibrium potential, suggesting that they were largely carried by Cl-. Altering extracellular K- or Na+ concentration did not alter currents; neither did replacement of intracellular K+ by Cs+ or intracellular Na+ by N-methyl-D-glucosamine. Anion-substitution experiments suggest the following permeability sequence, determined from shifts in tail current reversal potential: I- > NO3- > Br- > Cl- > acetate > isethionate > F- > glutamate. Currents were sensitive to the Cl- channel blockers chlorotoxin, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), and 4,4'-dinitrostilbene-2,2' disulfonic acid (DNDS), with chlorotoxin being most effective, yielding > 80% block at 590 nM. DIDS (100 microM) and DNDS (100 microM) reduced currents by 33.5 and 38.2%, respectively. Currents were also sensitive to Zn2+ (100 microM, 47% block) and Cd2- (25 microM, 42% block). Reducing extracellular Ca2+ concentration decreased outward currents by 58% and almost completely eliminated transients, suggesting that Cl- currents are Ca2+ dependent. Cl channel block resulted in altered cell proliferation as determined by [3H]thymidine incorporation, suggesting that these channels may be involved in astrocytoma growth control.
Ullrich
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N
Neurobiology Research Center, University of Alabama at Birmingham 35294, USA.
Sontheimer
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H
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D001254:Astrocytoma / Q000473:pathology / Q000503:physiopathology*; D001932:Brain Neoplasms / Q000473:pathology / Q000503:physiopathology*; D002455:Cell Division; D018118:Chloride Channels / Q000037:antagonists & inhibitors / Q000378:metabolism; D002712:Chlorides / Q000502:physiology*; D004553:Electric Conductivity; D006801:Humans; D012604:Scorpion Venoms / Q000494:pharmacology; D013267:Stilbenes / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D018118:Chloride Channels; D002712:Chlorides; D012604:Scorpion Venoms; D013267:Stilbenes; C091539:Chlorotoxin; C022306:4,4'-dinitro-2,2'-stilbenedisulfonic acid; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid