K+ inward rectifier currents in reactive astrocytes from adult rat brain

We characterized inward rectifier (K-IR) currents in reactive astrocytes ac tivated by CNS injury. We used primary cultures of reactive astrocytes obta ined from gelatin sponge implants in adult rat brains, a system that yielde d highly purified, homogeneous cultures with >95% of cells positive for GFA P, vimentin, and S-100 beta. Ionic channels were studied in 1-21-day-old pr imary cultures using a nystatin-perforated patch clamp technique. Fast Nacurrents were identified in <2% of cells. Most cells exhibited outward curr ents positive to -50 mV, with one component being sensitive to charybdotoxi n, iberiotoxin, and tetraethylammonium chloride, and another component bein g sensitive to 4-aminopyridine. Two populations of cells were distinguished , based on presence or absence of Ba2+-sensitive K-IR current negative to t he K+ reversal potential (E-k), with >80% of cells expressing K-IR currents . In contrast to previous reports on mammalian astrocytes, the current-volt age curve showed no appreciable current between Ek and -50 mV, reflecting s trong rectification by K-IR channels. The magnitude of K-IR current at - 13 0 mV (I-130) did not change significantly during 21 days in culture (123 ce lls), suggesting constitutive expression of KIR channels. The fraction of K -IR-negative cells was not affected by serum-starvation for 16-24 h. In cel ls with I-130 greater than or equal to -30 PA, the membrane potential was i nvariably near Ek and depolarized appreciably on addition of Ba2+, but in c ells 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 ma mmalian astrocytes. GLIA 27:213-225, 1999. (C) 1999 Wiley-Liss, Inc.