title: Astrocytic inwardly rectifying potassium currents are dependent on external sodium ions.
abstract: 1. Two subtypes of astrocytes that expressed distinctly different ion channel complements were identified in primary cultures from rat spinal cord and hippocampus using whole cell patch-clamp techniques. One population of cells expressed voltage-activated Na+ currents and displayed outwardly rectifying I-V relationships; the other group of cells had no detectable Na+ currents and pronounced inwardly rectifying I-V curves. 2. Astrocytes expressing Na+ currents were hyperpolarized (by approximately 7 mV) upon removal of external sodium, suggesting a resting Na+ conductance in these cells. In contrast, cells expressing primarily inwardly rectifying K+ currents, Kir, depolarized (by approximately 4-6 mV) in low-sodium solutions. 3. Removal of external Na+ ions increased the input resistance (189% of control) and reduced the whole cell current amplitude (60% of control at -120 mV) of cells with Kir. The reduction in current amplitude was dose-dependent and became apparent after a 10% reduction of [Na+]0 in 7/7 cells tested. At -120 mV, the effect was near maximal in response to a 50% reduction of [Na+]0. 4. The outward potassium currents of cells expressing Na(+)-currents were unaffected by removal of bath Na+. 5. We conclude that the conductance of glial inwardly rectifying K+ channels is dependent on external sodium ions via a mechanism that does not involve sodium ion permeation or blockade of these channels.
authors.affiliation: Neurobiology Research Center, University of Alabama School of Medicine, Birmingham 35294, USA.
authors.forename: C B
authors.initials: CB
authors.lastname: Ransom
authors.forename: H
authors.initials: H
authors.lastname: Sontheimer
authors.forename: D
authors.initials: D
authors.lastname: Janigro
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000502:physiology*; D004553:Electric Conductivity; D006624:Hippocampus / Q000166:cytology / Q000502:physiology*; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000502:physiology*; D013116:Spinal Cord / Q000166:cytology / Q000502:physiology*
chemical_list: D015221:Potassium Channels; D012964:Sodium