Voltage‐dependent potassium currents in hypertrophied rat astrocytes after a cortical stab wound

Changes in the membrane properties of reactive astrocytes in gliotic cortex induced by a stab wound were studied in brain slices of 21–28‐day‐old rats, using the patch‐clamp technique and were correlated with changes in resting extracellular K + concentration ([K + ] e ) measured in vivo using K + ‐selective microelectrodes. Based on K + current expression, three types of astrocytes were identified in gliotic cortex: A1 astrocytes expressing a time‐ and voltage‐independent K + current component and additional inwardly rectifying K + currents (K IR ); A2 astrocytes expressing a time‐ and voltage‐independent K + current component and additional delayed outwardly rectifying K + currents (K DR ); and complex astrocytes expressing K DR , K IR , and A‐type K + (K A ) currents and Na + currents (I Na ). Nestin/bromodeoxyuridine (BrdU)‐negative A1 astrocytes were found further than ∼100 μm from the stab wound and showed an upregulation of K IR currents within the first day post‐injury (PI), correlating with an increased resting [K + ] e . Their number declined from 62% of total astrocytes in control rats to 41% in rats at 7 days PI. Nestin/BrdU‐positive A2 astrocytes were found only within a distance of ∼100 μm from the stab wound and, in comparison to those in control rats, showed an upregulation of K DR currents. Their number increased from 8% of the total number of astrocytes in control rats to 39% 7 days PI. Both A1 and A2 astrocytes showed hypertrophied processes and increased GFAP staining, but an examination of cell morphology revealed greater changes in the surface/volume ratio in A2 astrocytes than in A1 astrocytes. Complex astrocytes did not display a hypertophied morphology; K IR currents in these cells were upregulated within 1 day PI, while the K DR , K A , and I Na currents were increased only 6 h PI. We conclude that two electrophysiologically, immunohistochemically, and morphologically distinct types of hypertrophied astrocytes are present at the site of a stab wound, depending on the distance from the lesion, and may have different functions in ionic homeostasis and/or regeneration. © 2004 Wiley‐Liss, Inc.