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Journal of Neuroscience, Vol 12, 1781-1788, Copyright © 1992 by Society for Neuroscience
Voltage-activated K+ currents in acutely isolated hippocampal astrocytes
FW Tse, DD Fraser, S Duffy and BA MacVicar
Neuroscience Research Group, University of Calgary, Alberta, Canada.
Hippocampal astrocytes were acutely isolated by papain treatment and
mechanical trituration. Astrocytes were identified by their distinctive
stellate morphology and immunocytochemical staining for glial fibrillary
acidic protein. The electrophysiological properties of these cells were
investigated using whole-cell voltage-clamp techniques. Three kinetically
and pharmacologically distinct voltage-activated K+ currents were
identified in most cells; they resembled the neuronal A- current, delayed
rectifier, and inward rectifier. The activation threshold of the A-current
was -40 mV with a time to peak that ranged from 10 msec at -20 mV to 6 msec
at 100 mV. Steady-state inactivation was observed when the holding
potential was positive to -100 mV. The current was half-inactivated at -60
mV and totally inactivated at -20 mV. The A-current was suppressed by
4-aminopyridine (4-AP). The delayed rectifier was activated by depolarizing
pulses more positive than -40 mV and had a half time of activation that
ranged from 18 msec at -20 mV to 10 msec at potentials more positive than
40 mV. This current did not inactivate during a 100 msec pulse and was
suppressed by extracellular tetraethylammonium (TEA). An inwardly
rectifying current was elicited by hyperpolarizing pulses more negative
than -80 mV. This current was not blocked by extracellular TEA or 4-AP and
was never observed in the presence of external Ba2+. Voltage-activated
inward Na+ currents were never observed. Voltage-activated K+ channels may
enhance the local K+ spatial buffering capabilities of the astrocyte
syncytium when extracellular [K+] increases during neuronal activity.
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