title: Ionic currents in cultured rat hypothalamic neurones.
abstract: 1. Dissociated neurones from embryonic rat hypothalamus were grown for several weeks in culture where they formed complex networks. These synaptically coupled networks were capable of generating synchronized bursting activity. Voltage-activated membrane currents were studied in these neurones using a patch clamp in the whole-cell configuration. 2. Outward currents were carried by K+ ions and consisted of an inactivating and a non-inactivating component. These components were similar to the transient K+ current (IA) and the delayed rectifier current (IK) reported in neurones from the postnatal rat hypothalamus. Application of Zn2+ (1 mM) blocked the transient component completely while reducing the non-inactivating component by only approximately 20%. 3. Inward currents were carried by Na+ and Ca2+ ions. Rapidly activating transient Na+ currents were activated at approximately -25 mV. TTX entirely blocked these currents at low concentration (300 nM). Voltage sensitivity of the Na+ conductance was 5.8 mV per e-fold change with half-maximal activation occurring at -8 mV. Na+ current kinetics could be well described by the Hodgkin-Huxley model (m3h). 4. With depolarizing pulses from a holding potential of -80 mV two Ca2+ current components with different ranges of activation were identified. Low voltage-activated (LVA, T-type) Ca2+ currents were activated at approximately -50 mV. High voltage-activated (HVA; also called L- or N-type) Ca2+ currents were observed at membrane potentials more positive to approximately -30 mV. LVA Ca2+ currents were observed in hypothalamic neurones that had developed a network of dendritic processes in the course of several weeks in culture. Activation and inactivation time constants of LVA Ca2+ currents were 15-25 ms and 30-100 ms (-30 to -45 mV). In contrast to HVA Ca2+ currents, no LVA Ca2+ currents were seen in neuronal somata obtained from the network cultures by mechanical dissociation. This suggests that most of the LVA Ca2+ channels are located on the dendritic tree rather than on the soma membrane. 5. HVA Ca2+ currents were maximal between 0 and +10 mV (external [Ca2+] = 5 mM). The time-to-peak was in the range of 1.7-5.4 ms (+30 to -10 mV). Tail currents following repolarization decayed monoexponentially with a time constant of approximately 210 microseconds. During 500 ms depolarizations, 90% of the current inactivated. The time course of inactivation showed two time constants of approximately 40 and approximately 700 ms.(ABSTRACT TRUNCATED AT 400 WORDS)
authors.affiliation: Max-Planck-Institut für biophysikalische Chemie, Göttingen, FRG.
authors.forename: T H
authors.initials: TH
authors.lastname: Müller
authors.forename: U
authors.initials: U
authors.lastname: Misgeld
authors.forename: D
authors.initials: D
authors.lastname: Swandulla
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology; D002478:Cells, Cultured; D004594:Electrophysiology; D007031:Hypothalamus / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000502:physiology
chemical_list: D015220:Calcium Channels; D015221:Potassium Channels; D015222:Sodium Channels; D012964:Sodium; D011188:Potassium; D002118:Calcium