title: Kinetic properties and functional dynamics of sodium channels during repetitive spiking in a slow pacemaker neuron.
abstract: We examined the kinetic properties of voltage-gated Na(+) channels and their contribution to the repetitive spiking activity of medullary raphé neurons, which exhibit slow pacemaking and strong spiking adaptation. The study is based on a combination of whole-cell patch-clamp, modeling and real-time computation. Na(+) currents were recorded from neurons in brain slices obtained from male and female neonatal rats, using voltage-clamp protocols designed to reduce space-clamp artifacts and to emphasize functionally relevant kinetic features. A detailed kinetic model was formulated to explain the broad range of transient and stationary voltage-dependent properties exhibited by Na(+) currents. The model was tested by injecting via dynamic clamp a model-based current as a substitute for the native TTX-sensitive Na(+) currents, which were pharmacologically blocked. The model-based current reproduced well the native spike shape and spiking frequency. The dynamics of Na(+) channels during repetitive spiking were indirectly examined through this model. By comparing the spiking activities generated with different kinetic models in dynamic-clamp experiments, we determined that state-dependent slow inactivation contributes significantly to spiking adaptation. Through real-time manipulation of the model-based current, we established that suprathreshold Na(+) current mainly controls spike shape, whereas subthreshold Na(+) current modulates spiking frequency and contributes to the pacemaking mechanism. Since the model-based current was injected in the soma, the results also suggest that somatic Na(+) channels are sufficient to establish the essential spiking properties of raphé neurons in vitro.
authors.affiliation: Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115, USA. Lorin_Milescu@hms.harvard.edu
authors.forename: Lorin S
authors.initials: LS
authors.lastname: Milescu
authors.forename: Tadashi
authors.initials: T
authors.lastname: Yamanishi
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Ptak
authors.forename: Jeffrey C
authors.initials: JC
authors.lastname: Smith
mesh_terms: D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D000831:Animals, Newborn; D001683:Biological Clocks / Q000502:physiology*; D055592:Biophysical Phenomena / Q000502:physiology*; D019256:Cadmium Chloride / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D066298:In Vitro Techniques; D008959:Models, Neurological; D009474:Neurons / Q000502:physiology*; D017711:Nonlinear Dynamics; D018408:Patch-Clamp Techniques / Q000379:methods; D011336:Probability; D011903:Raphe Nuclei / Q000166:cytology; D051381:Rats; D017207:Rats, Sprague-Dawley; D026941:Sodium Channel Blockers / Q000494:pharmacology; D015222:Sodium Channels / Q000187:drug effects / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology; D013997:Time Factors
chemical_list: D018691:Excitatory Amino Acid Antagonists; D026941:Sodium Channel Blockers; D015222:Sodium Channels; D013779:Tetrodotoxin; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D019256:Cadmium Chloride
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