title: Two distinct types of transient outward currents in area postrema neurons in rat brain slices.
abstract: We investigated the electrophysiological properties of the area postrema neurons in acutely prepared rat brain slices using the whole-cell patch-clamp technique. Two different types of transient outward potassium current (I(to)), fast and slow, were found in the area postrema. Both the decay time constant and rise time were significantly faster in the fast I(to) than in the slow I(to). Both current-clamp and voltage-clamp recordings revealed that the activation of fast and slow I(to) contributes to generation of the different spiking patterns, late spiking and interrupted spiking, respectively. The activation and inactivation of both I(to) were strongly voltage-dependent. Curve fitting by the Boltzmann equation revealed no significant difference in the activation and inactivation curves for each I(to) except that the slope factor of inactivation was larger for fast I(to). Both I(to) were suppressed dose-dependently by application of 4-aminopyridine. Each spiking pattern was enhanced when cells were held at a more hyperpolarized membrane potential, i.e. a longer latency of the first spike or longer interspike interval between the first and second spikes. The voltage-dependent modulation of the spiking pattern was consistent with the voltage-dependent activation of I(to). The present study shows significant subdivisions of the area postrema neurons distinguished by a difference in the kinetics of I(to) and spiking patterns. We discuss the role of I(to) as the ionic current underlying neuronal excitability.
authors.affiliation: Department of Oral Physiology, Okayama University Graduate School of Medicine and Dentistry, 2-5-1 Shikata-cho, Okayama 700-8525, Japan. mfuna@md.okayama-u.ac.jp
authors.forename: Makoto
authors.initials: M
authors.lastname: Funahashi
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Mitoh
authors.forename: Ryuji
authors.initials: R
authors.lastname: Matsuo
mesh_terms: D015761:4-Aminopyridine / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D002628:Chemoreceptor Cells / Q000166:cytology / Q000378:metabolism*; D004558:Electric Stimulation; D020546:Fourth Ventricle / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008526:Medulla Oblongata / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009924:Organ Culture Techniques; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism*; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology
chemical_list: D026902:Potassium Channel Blockers; D015221:Potassium Channels; D015761:4-Aminopyridine; D011188:Potassium