Voltage-dependent sodium and potassium currents in cultured trout astrocytes.
Voltage-gated ionic currents were recorded from cultured trout astrocytes with the whole-cell variation of the patch-clamp technique. In a subpopulation of astrocytes depolarizations above -40 mV activated a fast transient inward current that was identified as a sodium current by ion substitution experiments, its current reversal potential, and its TTX-sensitivity. Regarding threshold of activation, peak current voltage, and amplitude this current closely resembled those previously described for mammalian astrocytes. Voltage-dependence of inactivation and kinetics, however, markedly differed from the "glial-like" sodium current occurring in mammalian hippocampal or optic nerve astrocytes, since the sodium current of trout astrocytes exhibited a faster time course of activation and decay and a more depolarized steady-state inactivation curve with midpoints close to -60 mV. During a period of 2 weeks in culture the biophysical properties of the sodium current did not change significantly, albeit a continuous decrease in current density was observed. At depolarizing voltage steps positive to -40 mV, additionally voltage-gated potassium outward currents were evoked, which could be separated into a steady-state current with delayed rectifier properties and an inactivating component resembling the A-type current. Moreover, in a subpopulation of astrocytes an inward potassium current was elicited at hyperpolarizing potentials, which exhibited biophysical features consistent with the potassium inward rectifier of mammalian astrocytes.
Abt. Zoophysiologie, Universität Osnabrück, Germany.
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Glassmeier
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Jeserich
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Krüppel
D000818:Animals; D001253:Astrocytes / Q000502:physiology*; D002478:Cells, Cultured; D004594:Electrophysiology; D007150:Immunohistochemistry; D015640:Ion Channel Gating / Q000502:physiology; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D008807:Mice, Inbred BALB C; D017686:Oncorhynchus mykiss / Q000502:physiology*; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000502:physiology*; D015222:Sodium Channels / Q000502:physiology*
D015221:Potassium Channels; D015222:Sodium Channels