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Subthreshold inactivation of voltage‐gated K + channels modulates action potentials in neocortical bitufted interneurones from rats
Author(s) -
Korngreen Alon,
Kaiser Katharina M. M.,
Zilberter Yuri
Publication year - 2005
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2004.077032
Subject(s) - subthreshold conduction , excitatory postsynaptic potential , pyramidal cell , neuroscience , neurotransmission , biophysics , membrane potential , dendritic spike , chemistry , soma , physics , neocortex , hippocampal formation , synaptic potential , biology , inhibitory postsynaptic potential , voltage , receptor , biochemistry , transistor , quantum mechanics
Voltage‐gated K + channels perform many functions in integration of synaptic input and action potential (AP) generation. In this study we show that in bitufted interneurones from layer 2/3 of the somatosensory cortex, the height and width of APs recorded at the soma are sensitive to changes in the resting membrane potential, suggesting subthreshold activity of voltage‐gated conductances. Attributes of K + currents examined in nucleated patches revealed a fast subthreshold‐inactivating K + conductance (K f ) and a slow suprathreshold‐inactivating K + conductance (K s ). Simulations of these K + conductances, incorporated into a Hodgkin–Huxley‐type model, suggested that during a single AP or during low frequency trains of APs, subthreshold inactivation of K f was the primary modulator of AP shape, whereas during trains of APs the shape was governed to a larger degree by K s resulting in the generation of smaller and broader APs. Utilizing the facilitating function of unitary pyramidal‐to‐bitufted cell synaptic transmission, single back‐propagating APs were initiated in a bitufted interneurone by repeated stimulation of a presynaptic pyramidal cell. Ca 2+ imaging and dendritic whole‐cell recordings revealed that modulation of APs, which also affect the shape of back‐propagating APs, resulted in a change in dendritic Ca 2+ influx. Compartmental simulation of the back‐propagating AP suggested a mechanism for the modulation of the back‐propagating AP height and width by subthreshold activation of K f . We speculate that this signal may modulate retrograde GABA release and consequently depression of synaptic efficacy of excitatory input from neighbouring pyramidal neurones.