Simultaneous recordings of cytosolic Ca2+ level and membrane potential and current during the response to thyroliberin in clonal rat anterior pituitary cells

T. Iijima, O. Sand, T. Sekiguchi, G. Matsumoto

Research output: Contribution to journalArticlepeer-review

9 Citations (Scopus)

Abstract

The response to thyroliberin in prolactin-producing rat GH4C1 clonal cells was studied using fura-2 to monitor the cytosolic Ca2+ level ([Ca2+](i)) in single cells, combined with recordings of membrane potential and current. The average value of [Ca2+](i) was 109 nM (mean ± SD, n = 112), and evoked action potentials caused transient elevations of about 100 nM. At higher firing frequencies these transients merged to a sustained elevation. In 100% of the cells thyroliberin caused an instant rise in [Ca2+](i), peaking at 795 ± 300 nM (n = 112). This first phase of the thyroliberin response was associated with hyperpolarization in current clamp and outward current in voltage clamp, caused by the opening of Ca2+-activated K+ channels. In 75% of the cells the initial peak in [Ca2+](i) was followed by a prolonged plateau phase at 247 ± 76 nM (n = 84). In current clamp the second-phase elevation of [Ca2+](i) was linked to either a modest depolarization in combination with enhanced firing frequency or a more pronounced depolarization silent cells. This elevation of [Ca2+](i) was reversed by hyperpolarizing current injection. No second-phase elevation of [Ca2+](i) was observed during voltage clamp at a holding potential of -50 mV. Short exposure to Ca2+-free conditions eliminated the second-phase elevation in [Ca2+](i), whereas the first phase remained intact. Our experiments show a direct relationship between electrical activity and [Ca2+](i) in the GH4C1 cells. The second-phase elevation of [Ca2+](i) caused by thyroliberin is the result of influx through voltage-sensitive Ca2+ channels, without involving agonist-gated channels.

Original languageEnglish
Pages (from-to)269-278
Number of pages10
JournalActa Physiologica Scandinavica
Volume140
Issue number2
DOIs
Publication statusPublished - 1990
Externally publishedYes

Keywords

  • Action potential
  • Anterior pituitary
  • Calcium
  • Fura-2
  • Lactotrophs
  • Membrane current
  • Membrane potential
  • Thyroliberin

ASJC Scopus subject areas

  • Physiology

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