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ASC93b
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Literature
38 records
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pyramidal neurons from rat and cat sensorimotor cortex.
rat and cat sensorimotor cortex using either the thin slice preparation or
acutely isolated neurons. Single-channel recordings were obtained in the
cell-attached and inside-out configuration of the patch-clamp technique. Na+
channels had a conductance of about 16 pS. Patches always contained several
Na+ channels, usually 4-12. In both preparations, long depolarizing pulses
revealed two distinct patterns of late Na+ channel activity following
transient openings. (1) Na+ channels displayed sporadic brief late openings
sometimes clustered to "minibursts" of 10-40 msec. These events
occurred at a low frequency, yielding open probability (NPo) values below 0.01
(mean = 0.0034). (2) In the second gating mode, an individual Na+ channel in
the patch failed to inactivate and produced a burst of openings often lasting
to the end of the pulse. This behavior was observed in about 1% of
depolarizations. Shifts to the bursting mode were usually confined to a single
400 msec pulse, but rarely occurred during two or more consecutive pulses
applied at 2 sec intervals. Sustained bursts did not require preceding
transient openings to occur since they were also observed during slow
depolarizing voltage ramps. The similar incidence of inactivation failures in
cell-attached versus inside-out recordings suggests that the bursting mode is
a property of the channel and/or adjacent membrane-bound structures.
Calculations indicate that brief late openings and rare sustained bursts
suffice to generate a small but significant whole-cell current. Since the Na+
channels mediating early, brief late, and sustained openings were identical in
terms of their elementary electrical properties, we propose that the fast and
the persistent Na+ currents of cortical pyramidal cells are generated by an
electrophysiologically uniform population of Na+ channels that can
individually switch between different gating modes.
channel population.
