title: Ionic channel mechanisms mediating the intrinsic excitability of Kenyon cells in the mushroom body of the cricket brain.
abstract: Intrinsic neurons within the mushroom body of the insect brain, called Kenyon cells, play an important role in olfactory associative learning. In this study, we examined the ionic mechanisms mediating the intrinsic excitability of Kenyon cells in the cricket Gryllus bimaculatus. A perforated whole-cell clamp study using β-escin indicated the existence of several inward and outward currents. Three types of inward currents (INaf, INaP, and ICa) were identified. The transient sodium current (INaf) activated at -40 mV, peaked at -26 mV, and half-inactivated at -46.7 mV. The persistent sodium current (INaP) activated at -51 mV, peaked at -23 mV, and half-inactivated at -30.7 mV. Tetrodotoxin (TTX; 1 μM) completely blocked both INaf and INaP, but 10nM TTX blocked INaf more potently than INaP. Cd(2+) (50 μM) potently blocked INaP with little effect on INaf. Riluzole (>20 μM) nonselectively blocked both INaP and INaf. The voltage-dependent calcium current (ICa) activated at -30 mV, peaked at -11.3 mV, and half-inactivated at -34 mV. The Ca(2+) channel blocker verapamil (100 μM) blocked ICa in a use-dependent manner. Cell-attached patch-clamp recordings showed the presence of a large-conductance Ca(2+)-activated K(+) (BK) channel, and the activity of this channel was decreased by removing the extracellular Ca(2+) or adding verapamil or nifedipine, and increased by adding the Ca(2+) agonist Bay K8644, indicating that Ca(2+) entry via the L-type Ca(2+) channel regulates BK channel activity. Under the current-clamp condition, membrane depolarization generated membrane oscillations in the presence of 10nM TTX or 100 μM riluzole in the bath solution. These membrane oscillations disappeared with 1 μM TTX, 50 μM Cd(2+), replacement of external Na(+) with choline, and blockage of Na(+)-activated K(+) current (IKNa) with 50 μM quinidine, indicating that membrane oscillations are primarily mediated by INaP in cooperation with IKNa. The plateau potentials observed either in Ca(2+)-free medium or in the presence of verapamil were eliminated by blocking INaP with 50 μM Cd(2+). Taken together, these results indicate that INaP and IKNa participate in the generation of membrane oscillations and that INaP additionally participates in the generation of plateau potentials and initiation of spontaneous action potentials. ICa, through L-type Ca(2+) channels, was also found to play a role in the rapid membrane repolarization of action potentials by functional coupling with BK channels.
authors.affiliation: Department of Biology, Tokyo Gakugei University, Tokyo, Japan.
authors.forename: Shigeki
authors.initials: S
authors.lastname: Inoue
authors.affiliation: Department of Biology, Tokyo Gakugei University, Tokyo, Japan.
authors.forename: Kaoru
authors.initials: K
authors.lastname: Murata
authors.affiliation: Department of Biology, Tokyo Gakugei University, Tokyo, Japan.
authors.forename: Aiko
authors.initials: A
authors.lastname: Tanaka
authors.affiliation: Department of Biology, Tokyo Gakugei University, Tokyo, Japan.
authors.forename: Eri
authors.initials: E
authors.lastname: Kakuta
authors.affiliation: Department of Biology, Tokyo Gakugei University, Tokyo, Japan.
authors.forename: Saori
authors.initials: S
authors.lastname: Tanemura
authors.affiliation: Department of Biology, Tokyo Gakugei University, Tokyo, Japan.
authors.forename: Shiori
authors.initials: S
authors.lastname: Hatakeyama
authors.affiliation: Department of Biology, Tokyo Gakugei University, Tokyo, Japan.
authors.forename: Atsunao
authors.initials: A
authors.lastname: Nakamura
authors.affiliation: Department of Biology, Tokyo Gakugei University, Tokyo, Japan.
authors.forename: Chihiro
authors.initials: C
authors.lastname: Yamamoto
authors.affiliation: Department of Biology, Tokyo Gakugei University, Tokyo, Japan.
authors.forename: Masaharu
authors.initials: M
authors.lastname: Hasebe
authors.affiliation: Department of Biology, Tokyo Gakugei University, Tokyo, Japan.
authors.forename: Kumiko
authors.initials: K
authors.lastname: Kosakai
authors.affiliation: Department of Biology, Tokyo Gakugei University, Tokyo, Japan. Electronic address: myoshi@u-gakugei.ac.jp.
authors.forename: Masami
authors.initials: M
authors.lastname: Yoshino
mesh_terms: D000818:Animals; D001921:Brain / Q000187:drug effects; D006135:Gryllidae / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D024521:Mushroom Bodies / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques
chemical_list: D007473:Ion Channels
keywords: Ca(2+) current; Ca(2+)-activated K(+) channel; Kenyon cell; Membrane oscillations; Persistent Na(+) channel; Plateau potential