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Journal of Neuroscience, Vol 7, 1166-1177, Copyright © 1987 by Society for Neuroscience
Long-term modifiability of anomalous and delayed rectification in guinea pig inferior olivary neurons
Y Yarom and R Llinas
Delayed and anomalous rectification was studied in inferior olivary (I.O.)
neurons in guinea pig brain stem slices maintained in vitro.
Hyperpolarization of the I.O. cell beyond rest membrane potential was
accompanied by anomalous rectification (AR). This consisted of 2 parts: an
instantaneous and a time-dependent component. The "instantaneous" component
was blocked by bath addition of Ba2+ or Cs+ and demonstrated inactivation
following prolonged hyperpolarization. The time-dependent component,
referred to as the gK(ol), was blocked by harmaline in concentrations of
0.1 mg/ml or by substitution of Co2+, Cd2+, or Mn2+ for Ca2+ in the bath.
The gK(ol) was blocked by extracellular Cs+ but not by Ba2+. Delayed
rectification (DR), consisting of 2 distinct components, was observed after
membrane depolarization by more than 10 mV with respect to rest (usually at
-65 mV). One of the components of the DR was found to be quite similar to
the classical gK. It did not demonstrate significant inactivation with
membrane potential change and was reduced by Ba2+ or tetraethylammonium
(TEA). A second component of the DR demonstrated voltage-dependent
inactivation and was thus referred to as gK(inact). This inactivation
determined by current-clamp measurements had a sigmoidal time course, with
approximately a 1 sec onset latency and a half-time to peak of 7 sec. The
inactivation of gK(inact) outlasted current injection for tens of seconds
to several minutes, depending on the duration and amplitude of the
preceding depolarization. During this period, I.O. neurons could be easily
activated and demonstrated full dendritic spikes following current
injection or excitatory synaptic input that had previously been
subthreshold for spike initiation. The inactivation component of the DR was
removed by prolonged membrane hyperpolarization beyond rest. gK(inact) was
blocked by 4-aminopyridine (4-AP; 100 microM) but not by Ba2+. This
inactivation was dependent on the presence of extracellular Ca2+ or Ba2+.
Addition of Co2+ or Cd2+ to the bath did not block gK(inact) but did
prevent its inactivation. The modulatory effects of these different
membrane conductances on the integrative properties of I.O. neurons are
described. The long duration of the inactivation of DR and AR is considered
as the basis for a dynamic long-term modulation of the electroresponsive
and integrated properties of I.O. neurons.
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