Research paper
Vasopressin induces frequency-modulated repetitive calcium transients in single insulin-secreting hit cells

https://doi.org/10.1016/0303-7207(95)03474-LGet rights and content

Abstract

Ca2+ is central to the stimulation of insulin secretion from pancreatic β-cells. Arginine-vasopressin (AVP) may participate in the modulation of insulin release. In the present study, the AVP-induced changes in cytosolic free Ca2+ ([Ca2+]i) were investigated in single fura-2 loaded insulin-secreting HIT cells. Stimulation with AVP (0.1–5 nM) caused repetitive Ca2+ transients. The frequency but not the amplitude of the Ca2+ transients was modulated by the concentration of AVP. High concentrations of AVP (10–100 nM) triggered a biphasic rise in [Ca2+]i. In Ca2+-free medium AVP caused only one or two Ca2+ transients. Withdrawal of extracellular Ca2+ rapidly abolished the AVP-induced Ca2+ transients in all cells tested. The Ca2+ channel blocker, verapamil (50 μM), reduced amplitude and frequency of the Ca2+ transients by about 25% and 60%, respectively, and terminated the Ca2+ transients in 2 of 6 cells. When HIT cells were incubated in Ca2+-free medium, and extracellular Ca2+ was restored, there was a small increase in [Ca2+]i. If, however, the agonist-sensitive Ca2+ pool was functionally depleted by repetitive stimulation with high concentrations of AVP or thapsigargin in Ca2+-free medium before extracellular Ca2+ was restored, an agonist-independent increase in [Ca2+]i was observed, which was transiently larger than in the control cells, and was mainly preserved in the presence of verapamil. Thus, depletion of the agonistsensitive Ca2+ pool enhances the influx of extracellular Ca2+ through a Ca2+ entry mechanism independent from verapamil-sensitive voltage-dependent Ca2+ channels (VDCC). In conclusion, the AVP-induced Ca2+ response in single HIT cells is periodic in nature with frequency-modulated repetitive Ca2+ transients. AVP mobilizes Ca2+ from intracellular pools, but influx of extracellular Ca2+ partly through verapamil-sensitive VDCC, and partly through an additional, VDCC-independent pathway, which could be controlled by the filling state of the agonist-sensitive Ca2+ pool, is required for maintaining the repetitive nature of the Ca2+ response.

References (39)

  • J.A. Amico et al.

    Am. J. Med. Sci.

    (1988)
  • P. Arkhammar et al.

    J. Biol. Chem.

    (1994)
  • Z.-Y. Gao et al.

    J. Biol. Chem.

    (1990)
  • E. Grapengiesser et al.

    Biochem. Biophys. Res. Commun.

    (1988)
  • G. Grynkiewicz et al.

    J. Biol. Chem.

    (1985)
  • R.J. Hajjar et al.

    J. Biol. Chem.

    (1991)
  • G. Li et al.

    J. Biol. Chem.

    (1992)
  • E.A. Longo et al.

    J. Biol. Chem.

    (1991)
  • M.E. Monaco et al.

    Biochem. Biophys. Res. Commun.

    (1988)
  • M. Prentki et al.

    J. Biol. Chem.

    (1988)
  • R. Regazzi et al.

    J. Biol. Chem.

    (1990)
  • P. Rorsman et al.

    FEBS Lett.

    (1984)
  • H. Takemura et al.

    J. Biol. Chem.

    (1989)
  • J.-M. Theler et al.

    J. Biol. Chem.

    (1992)
  • J.L. Wang et al.

    J. Biol. Chem.

    (1993)
  • C.B. Wollheim et al.

    J. Biol. Chem.

    (1984)
  • C. Ämmälä et al.

    Nature

    (1991)
  • A.E. Boyd et al.

    J. Clin. Invest.

    (1986)
  • K.S.R. Cuthbertson
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