Direct demonstration of persistent Na+ channel activity in dendritic processes of mammalian cortical neurones

摘要

class="enumerated" style="list-style-type:decimal">Single Na⁺ channel activity was recorded in patch-clamp, cell-attached experiments performed on dendritic processes of acutely isolated principal neurones from rat entorhinal-cortex layer II. The distances of the recording sites from the soma ranged from ≈20 to ≈100 μm.Step depolarisations from holding potentials of −120 to −100 mV to test potentials of −60 to +10 mV elicited Na⁺ channel openings in all of the recorded patches (n= 16).In 10 patches, besides transient Na⁺ channel openings clustered within the first few milliseconds of the depolarising pulses, prolonged and/or late Na⁺ channel openings were also regularly observed. This ‘persistent’ Na⁺ channel activity produced net inward, persistent currents in ensemble-average traces, and remained stable over the entire duration of the experiments (≈9 to 30 min).Two of these patches contained <= 3 channels. In these cases, persistent Na⁺ channel openings could be attributed to the activity of one single channel.The voltage dependence of persistent-current amplitude in ensemble-average traces closely resembled that of whole-cell, persistent Na⁺ current expressed by the same neurones, and displayed the same characteristic low threshold of activation.Dendritic, persistent Na⁺ channel openings had relatively high single-channel conductance (≈20 pS), similar to what is observed for somatic, persistent Na⁺ channels.We conclude that a stable, persistent Na⁺ channel activity is expressed by proximal dendrites of entorhinal-cortex layer II principal neurones, and can contribute a significant low-threshold, persistent Na⁺ current to the dendritic processing of excitatory synaptic inputs.