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FG96
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Literature
38 records
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of mouse neocortical slices.
somatosensory neocortex, tetrodotoxin (TTX)-sensitive persistent Na+ current
(INaP) was studied by blocking K+ currents with intracellular Cs+ and Ca2+
currents with extracellular Cd2+. During slow voltage ramps, INaP began to
activate at around -60 mV, and attained a peak at around -25 mV. The peak
amplitude of INaP varied widely from cell to cell (range 60-3,160 pA; median
308 pA, n = 77). At potentials more positive than -35 mV, INaP in all cells
was superimposed on a large, TTX-resistant outward current. 2. In hybrid clamp
experiments, INaP was significantly reduced by a preceding high-frequency
train of spikes. 3. INaP underwent pronounced slow inactivation, which was
revealed by systematically varying the ramp speed between 233 and 2.33 mV/s,
or varying the duration of a depolarizing prepulse between 0.1 and 10 s. 4.
Onset of slow inactivation at +20 mV was monoexponential with tau = 2.06 s (n
= 17 cells). Recovery from slow inactivation was voltage dependent. It
followed a monoexponential time course with tau = 2.31 s (n = 6) at -70 mV and
tau = 1.10 s (n = 4) at -90 mV. These values are not significantly different
than values previously reported for slow inactivation of fast-inactivating
INa. 5. Slow inactivation of neocortical INaP will influence all neuronal
functions in which this current plays a role, including spike threshold
determination, synaptic integration, and active propagation in dendrites. The
kinetics of slow inactivation suggest that it may be a factor not only during
extremely intense spiking, but also during periods of "spontaneous"
activity.
