Biophysical and pharmacological characterization of chloride
currents in human astrocytoma cells.
Ullrich, Nicole, and Harald Sontheimer.
Neurobiology Research Center, University of Alabama at Birmingham,
Birmingham, AL 35294; Interdepartmental Neuroscience Program, Yale
University School of Medicine, New Haven, CT 06510
APStracts 2:0407C, 1995.
Expression of voltage activated ion channels was studied in primary
cultures from 7 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 greater than 45mV and
showed outward transients upon termination of voltage steps. Currents
reversed at the Cl- equilibrium potential, suggesting that they were
largely carried by Cl- ions. Altering [K+]o or [Na+]o did not alter
currents; neither did replacement of [K+]i by Cs+ or [Na+]i by NMDG.
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, DIDS, and DNDS, with chlorotoxin being most effective,
yielding >80% block at 590nM. DIDS (100[mu]M) and DNDS
(100[mu]M) reduced currents by 33.5% and 38.2% respectively. Currents
were also sensitive to zinc (100[mu]M, 47% block) and cadmium
(25[mu]M, 42% block). Reducing [Ca2+]o 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.
Received 21 September 1995; accepted in final form 13 November
1995.
APS Manuscript Number C573-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 8 December 95