BIOPHYSICAL AND PHARMACOLOGICAL CHARACTERIZATION OF CHLORIDE CURRENTSIN HUMAN ASTROCYTOMA-CELLS

Expression of voltage-activated ion channels was studied in primary cu ltures from seven freshly resected human primary brain tumors and in a n established human astrocytoma cell line, STTG1. Astrocytoma cells co nsistently 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- equilibr ium potential, suggesting that they were largely carried by Cl-. Alter ing extracellular K+ or Na+ concentration did not alter currents; neit her did replacement of intracellular K+ by Cs+ or intracellular Na+ by N-methyl-D-glucosamine. Anion-substitution experiments suggest the fo llowing 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 chlo rotoxin, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), and 4,4'-dinitrostilbene-2,2'disulfonic acid (DNDS), with chlorotoxin bein g most effective, yielding >80% block at 590 nM. DIDS (100 mu M) and D NDS (100 mu M) reduced currents by 33.5 and 38.2%, respectively. Curre nts were also sensitive to Zn2+ (100 mu M, 47% block) and Cd2+ (25 mu M, 42% block). Reducing extracellular Ca2+ concentration decreased out ward currents by 58% and almost completely eliminated transients, sugg esting that Cl- currents are Ca2+ dependent. Cl- channel block resulte d in altered cell proliferation as determined by [H-3]thymidine incorp oration, suggesting that these channels may be involved in astrocytoma growth control.