Direct demonstration of persistent Na+ channel activity in dendritic processes of mammalian cortical neurones.
1. 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 approximately 20 to approximately 100 microm. 2. 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). 3. 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 ( approximately 9 to 30 min). 4. Two of these patches contained < or = 3 channels. In these cases, persistent Na+ channel openings could be attributed to the activity of one single channel. 5. 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. 6. Dendritic, persistent Na+ channel openings had relatively high single-channel conductance ( approximately 20 pS), similar to what is observed for somatic, persistent Na+ channels. 7. 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.
Magistretti
J
J
Department of Neurology and Neurosurgery, McGill University, Montreal, Quebec, Canada. neurofis@tin.it
Ragsdale
D S
DS
Alonso
A
A
D000465:Algorithms; D000818:Animals; D002540:Cerebral Cortex / Q000166:cytology / Q000378:metabolism*; D003712:Dendrites / Q000378:metabolism*; D004594:Electrophysiology; D018728:Entorhinal Cortex / Q000166:cytology / Q000378:metabolism; D066298:In Vitro Techniques; D008297:Male; D009474:Neurons / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D051381:Rats; D020318:Rats, Long-Evans; D015222:Sodium Channels / Q000378:metabolism*
D015222:Sodium Channels