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 (KIR); A2 astrocytes expressing a time‐ and voltage‐independent K+ current component and additional delayed outwardly rectifying K+ currents (KDR); and complex astrocytes expressing KDR, KIR, and A‐type K+ (KA) currents and Na+ currents (INa). Nestin/bromodeoxyuridine (BrdU)‐negative A1 astrocytes were found further than ∼100 μm from the stab wound and showed an upregulation of KIR 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 KDR 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; KIR currents in these cells were upregulated within 1 day PI, while the KDR, KA, and INa 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 regeneratio