Elsevier

Neuroscience

Volume 70, Issue 3, February 1996, Pages 729-738
Neuroscience

Characterization of hypothalamic low-voltage-activated Ca channels based on their functional expression in Xenopus oocytes

https://doi.org/10.1016/S0306-4522(96)83010-7Get rights and content

Abstract

Ca-channel currents expressed in Xenopus oocytes by means of messenger RNA extracted from rat thalamohypothalamic complex were studied using the double microelectrode technique. Currents were recorded in Cl-free extracellular solutions with 40 mM Ba2+ as a charge carrier. In response to depolarizations from a very negative holding potential (Vh = −120 mV), inward Ba2+ current activated at around −80 mV, peaked at −30 to −20 mV and reversed at +50 mV indicating that it may be transferred through the low voltage-activated calcium channels. The time-dependent inactivation of the current during prolonged depolarization to −20 mV was quite slow and followed a single exponential decay with a time-constant of 1550 ms and a maintained component constituting 30% of the maximal amplitude. The current could not be completely inactivated at any holding potential. As expected for low voltage-activated current, steady-state inactivation curve shifted towards negative potentials. It could be described by the Boltzmann equation with half inactivation potential −78 mV, slope factor 15 mV and maintained level 0.3. Expressed Ba2+ current could be blocked by flunarizine with Kd = 0.42 μM, nifedipine, Kd = 10 μM, and amiloride at 500 μM concentration. Among inorganic Ca-channel blockers the most potent was La3+ (Kd = 0.48 μM) while Cd2+ and Ni2+ were not very discriminative and almost 1000-fold less effective than La3+ (Kd = 0.52 mM and Kd = 0.62 mM, respectively).

Our data show that messenger RNA purified from thalamohypothalamic complex induces expression in the oocytes of almost exclusively low voltage-activated calcium channels with voltage-dependent and pharmacological properties very similar to those observed for T-type calcium current in native hypothalamic neurons, though kinetic properties of the expressed and natural currents are somewhat different.

References (36)

  • C.M. Armstrong et al.

    Two distinct populations of calcium channels in a clonal line of pituitary cells

    Science

    (1985)
  • M.E. Barish

    A transient calcium-dependent chloride current in immature Xenopus oocyte

    J. Physiol.

    (1983)
  • B.P. Bean

    Classes of calcium channels in vertebrate cells

    A. Rev. Physiol.

    (1989)
  • M. Bertolino et al.

    The central role of voltage-activated and receptor operated calcium channels in neuronal cells

    A. Rev. Pharmac. Toxic.

    (1992)
  • J.L. Bossu et al.

    Depolarization elicits two distinct calcium currents in vertebrate sensory neurons

    Pflügers Arch.

    (1985)
  • E. Carbone et al.

    A low-voltage activated fully inactivating Ca channel in vertebrate sensory neurons

    Nature

    (1984)
  • E. Carbone et al.

    Kinetics and selectivity of a low-voltage-activated calcium current in chick and rat sensory neurons

    J. Physiol.

    (1987)
  • I. Dzhura et al.

    Expression of low-voltage activated Ca channels from rat brain neurones in Xenopus oocytes

    NeuroReport

    (1994)
  • Cited by (18)

    • Ion Channels

      2018, Comprehensive Toxicology: Third Edition
    • Ion Channels

      2010, Comprehensive Toxicology, Second Edition
    • Selectivity signatures of three isoforms of recombinant T-type Ca<sup>2+</sup> channels

      2007, Biochimica et Biophysica Acta - Biomembranes
      Citation Excerpt :

      Oocytes were used for the experiments 5 days after cRNA injection, since this time was required for maximal T-type Ca2+-channel current expression (data not shown). Membrane currents in the oocytes were recorded using a conventional double-microelectrode voltage-clamp technique as described before [17]. “Voltage recording” and “current passing” microelectrodes were pulled from borosilicate glass and had resistance of ∼ 3 MΩ and ∼ 1 MΩ, respectively, when filled with 3 M KCl.

    • Contrasting the effects of nifedipine on subtypes of endogenous and recombinant T-type Ca<sup>2+</sup> channels

      2005, Biochemical Pharmacology
      Citation Excerpt :

      Stage V and VI oocytes from adult female Xenopus laevis frogs were used for the recombinant T-type Ca2+-channel expression. The procedures for oocyte isolation, maintenance and injection did not differ from those detailed elsewhere [10]. The volume of injected Cav3.1, Cav3.2 or Cav3.3 cRNA solution (0.2 μg/μl) was usually 50 nl per oocyte.

    View all citing articles on Scopus
    View full text