We characterized inward rectifier (K(IR)) currents in reactive astrocytes activated by CNS injury. We used primary cultures of reactive astrocytes obtained from gelatin sponge implants in adult rat brains, a system that yielded highly purified, homogeneous cultures with >95% of cells positive for GFAP, vimentin, and S-100beta. Ionic channels were studied in 1-21-day-old primary cultures using a nystatin-perforated patch clamp technique. Fast Na(+) currents were identified in <2% of cells. Most cells exhibited outward currents positive to -50 mV, with one component being sensitive to charybdotoxin, iberiotoxin, and tetraethylammonium chloride, and another component being sensitive to 4-aminopyridine. Two populations of cells were distinguished, based on presence or absence of Ba(2+)-sensitive K(IR) current negative to the K(+) reversal potential (E(k)), with >80% of cells expressing K(IR) currents. In contrast to previous reports on mammalian astrocytes, the current-voltage curve showed no appreciable current between E(k) and -50 mV, reflecting strong rectification by K(IR) channels. The magnitude of K(IR) current at -130 mV (I(-)(130)) did not change significantly during 21 days in culture (123 cells), suggesting constitutive expression of K(IR) channels. The fraction of K(IR)-negative cells was not affected by serum-starvation for 16-24 h. In cells with I(-)(130) >/= -30 pA, the membrane potential was invariably near E(k) and depolarized appreciably on addition of Ba(2+), but in cells with I(-)(130) < -30 pA, resting potentials ranged from -40 mV to -90 mV. We conclude that most adult reactive astrocytes constitutively express K(IR) channel(s) that exhibit strong rectification not previously observed in mammalian astrocytes.
Copyright 1999 Wiley-Liss, Inc.