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Differential modulation of TTX-sensitive and TTX-resistant Na+ channels in spinal cord astrocytes following activation of protein kinase C

CL Thio and H Sontheimer
Journal of Neuroscience 1 November 1993, 13 (11) 4889-4897; https://doi.org/10.1523/JNEUROSCI.13-11-04889.1993
CL Thio
Department of Neurology, Yale University, School of Medicine, New Haven, Connecticut 06510.
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H Sontheimer
Department of Neurology, Yale University, School of Medicine, New Haven, Connecticut 06510.
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Abstract

TTX-sensitive (TTX-S) and TTX-resistant (TTX-R) Na+ currents are expressed in high densities (2–8 channels/microns2) in astrocytes cultured from neonatal rat spinal cord. The two Na+ current types differ up to 1000-fold in their TTX sensitivity and additionally have different steady-state activation (g-V) and inactivation (h infinity) curves. Expression of TTX-S and TTX-R Na+ currents is confined to morphologically distinguishable subtypes of astrocytes, allowing characterization of the two types of Na+ currents in isolation: stellate cells express TTX-S Na+ currents and flat pancake cells express TTX-R Na+ currents. Activation of protein kinase C (PKC) by phorbol 12-myristate 13-acetate (PMA) exhibited different effects on TTX-S and TTX-R Na+ currents. PMA reduced peak TTX-S Na+ currents by 25– 60%; in contrast, PMA potentiated peak TTX-R Na+ currents by 60–150%. These effects developed within minutes, and were typically not reversible. PMA effects were voltage dependent, and shifted steady- state Na+ current activation of TTX-R and TTX-S currents by 6 and 18 mV, respectively, but without affecting their steady-state current inactivation (h infinity). PMA treatment also changed Na+ current kinetics. TTX-R current activation (tau m) was faster and current inactivation (tau h) changed from a single- to a bi-exponential after PMA exposure, suggesting that PKC phosphorylation may have activated formerly quiescent Na+ channels. In contrast, TTX-S current activation (tau m) was unchanged, and current inactivation (tau h), on average, decreased by 50% following PMA exposure.(ABSTRACT TRUNCATED AT 250 WORDS)

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The Journal of Neuroscience: 13 (11)
Journal of Neuroscience
Vol. 13, Issue 11
1 Nov 1993
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Differential modulation of TTX-sensitive and TTX-resistant Na+ channels in spinal cord astrocytes following activation of protein kinase C
CL Thio, H Sontheimer
Journal of Neuroscience 1 November 1993, 13 (11) 4889-4897; DOI: 10.1523/JNEUROSCI.13-11-04889.1993

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Differential modulation of TTX-sensitive and TTX-resistant Na+ channels in spinal cord astrocytes following activation of protein kinase C
CL Thio, H Sontheimer
Journal of Neuroscience 1 November 1993, 13 (11) 4889-4897; DOI: 10.1523/JNEUROSCI.13-11-04889.1993
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