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Journal of Neuroscience, Vol 16, 2532-2545, Copyright © 1996 by Society for Neuroscience
Whole-cell chloride currents in rat astrocytes accompany changes in cell morphology
CD Lascola and RP Kraig
Committee on Neurobiology, University of Chicago, Illinois 60637, USA.
Astrocytes can change shape dramatically in response to increased
physiological and pathological demands, yet the functional consequences of
morphological change are unknown. We report the expression of Cl- currents
after manipulations that alter astrocyte morphology. Whole- cell Cl-
currents were elicited after (1) rounding up cells by brief exposure to
trypsin; (2) converting cells from a flat polygonal to a process-bearing
(stellate) morphology by exposure to serum-free Ringer's solution; and (3)
swelling cells by exposure to hypo-osmotic solution. Zero-current
potentials approximated the Nernst for Cl-, and rectification usually
followed that predicted by the constant-field equation. We observed
heterogeneity in the activation and inactivation kinetics, as well as in
the relative degree of outward versus inward rectification. Cl-
conductances were inhibited by 4, 4- diisothiocyanostilbene-2,2'-disulfonic
acid (200 microM) and by Zn2+ (1 mM). Whole-cell Cl- currents were not
expressed in cells without structural change. We investigated whether
changes in cytoskeletal actin accompanying changes in astrocytic morphology
play a role in the induction of shape-dependent Cl- currents.
Cytochalasins, which disrupt actin polymers by enhancing actin-ATP
hydrolysis, elicited whole-cell Cl- conductances in flat, polygonal
astrocytes. In stellate cells, elevated intracellular Ca2+ (2 microM),
which can depolymerize actin, enhanced Cl- currents, and high intracellular
ATP (5 mM), required for repolymerization, reduced Cl- currents. Modulation
of Cl- current by Ca2+ and ATP was blocked by concurrent whole-cell
dialysis with phalloidin and DNase, respectively. Phalloidin stabilizes
actin polymers and DNase inhibits actin polymerization. Dialysis with
phalloidin also prevented hypo-osmotically activated Cl- currents. These
results demonstrate how the expression of astrocyte Cl- currents can be
dependent on cell morphology, the structure of actin, Ca2+ homeostasis, and
metabolism.
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