Ion channel expression by astrocytes in situ: Comparison of different CNS regions

Patch-clamp recordings were obtained in brain slices from 283 rat astrocyte s. The expression of voltage-activated whole-cell currents was compared in four different CNS regions (hippocampus, cerebral cortex, spinal cord, and cerebellum). Our data show that CNS astrocytes do not show significant regi onal differences in their ion channel complement. With the exception of cer ebellar Bergmann glial cells, essentially all astrocytes express a combinat ion of delayed rectifying outward K+ currents, transient A-type K+ currents , and small Naf currents. Developmentally, an increasing percentage of astr ocytes and Bergmann glial cells express inwardly rectifying K+ currents. We did not observe cells that were passive, i.e., lacking voltage-activated c urrents. A few cells that appeared "passive" in initial recordings showed v oltage-activated K+ currents after off-line leak subtraction. The heterogen eity observed in the ion channel complement was found to be identical when cell-to-cell variations observed within a given CNS region and between vari ous CNS regions were compared, suggesting a common and fairly stereotypical complement of ion channels in CNS astrocytes. Ion channel expression in Be rgmann glial cells differed from that of all other CNS regions studied. The se cells typically showed very low input resistances attributable to a sig significant time- and voltage-independent resting K+ conductance. However, as with electrophysiologically "passive"-appearing astrocytes, Bergmann gli al cells showed expression of delayed rectifying K+ currents after off-line leak subtraction. Inwardly rectifying K+ currents were observed in Bergman n glial cells after postnatal day 17. Collectively, our data suggest that a ll astrocytes contain voltage-gated ion channels that display a common patt ern of expression during development. GLIA 30:27-38, 2000. (C) 2000 Wiley-L iss, Inc.