Subthreshold inactivation of voltage-gated K+ channels modulates action potentials in neocortical bitufted interneurones from rats

• Published in: The Journal of physiology Vol. 562; no. 2; pp. 421 - 437
• Main Authors: Korngreen, Alon, Kaiser, Katharina M. M., Zilberter, Yuri
• Format: Journal Article
• Language: English
• Published: 9600 Garsington Road , Oxford , OX4 2DQ , UK The Physiological Society 15.01.2005; Blackwell Science Ltd; Blackwell Science Inc
• Subjects: Action Potentials - drug effects; Action Potentials - physiology; Algorithms; Animals; Cell Physiology; Computer Simulation; Dendrites - physiology; Diagnostic Imaging; In Vitro Techniques; Interneurons - drug effects; Interneurons - ultrastructure; Ion Channel Gating - physiology; Neocortex - drug effects; Neocortex - physiology; Neocortex - ultrastructure; Potassium Channels - physiology; Potassium Channels - ultrastructure; Pyramidal Cells - drug effects; Pyramidal Cells - physiology; Rats; Somatosensory Cortex - cytology; Somatosensory Cortex - drug effects
• ISSN: 0022-3751; 1469-7793; 1469-7793
• DOI: 10.1113/jphysiol.2004.077032

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.