title: Whole-cell chloride currents in rat astrocytes accompany changes in cell morphology.
abstract: 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.
authors.affiliation: Committee on Neurobiology, University of Chicago, Illinois 60637, USA.
authors.forename: C D
authors.initials: CD
authors.lastname: Lascola
authors.forename: R P
authors.initials: RP
authors.lastname: Kraig
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000200:Action Potentials / Q000502:physiology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001253:Astrocytes / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology; D002478:Cells, Cultured; D018118:Chloride Channels / Q000502:physiology*; D007150:Immunohistochemistry; D018408:Patch-Clamp Techniques; D051381:Rats; D015032:Zinc / Q000494:pharmacology
chemical_list: D018118:Chloride Channels; D000255:Adenosine Triphosphate; D015032:Zinc; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D002118:Calcium