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Pflügers Archiv

, Volume 428, Issue 1, pp 51–59 | Cite as

Oxytocin mobilizes calcium from a unique heparin-sensitive and thapsigargin-sensitive store in single myometrial cells from pregnant rats

  • S. Arnaudeau
  • N. Leprêtre
  • J. Mironneau
Excitable Tissues and Central Nervous Physiology

Abstract

Intracellular free Ca2+ concentration ([Ca2+]i) was monitored using the fluorescence from the dye Fura-2-AM in single myometrial cells from pregnant rats. Oxytocin and acetylcholine applied to the cell evoked an initial peak in [Ca2+]i followed by a smaller sustained rise which was rapidly terminated upon removal of acetylcholine or persisted after oxytocin removal. A Ca2+ channel blocker (oxodipine) and external Ca2+ removal decreased both the transient and sustained rises in [Ca2+]i suggesting that Ca2+ influx through L-type Ca2+ channels participated in the global Ca2+ response induced by oxytocin. However, the initial peak in [Ca2+]i produced by oxytocin was mainly due to Ca2+ store release: it was abolished by inclusion of heparin [which blocks inositol 1,4,5-trisphosphate (InsP3) receptors] in the pipette (whole-cell recording mode of patch-clamp) and external application of thapsigargin (which blocks sarcoplasmic reticulum Ca2+-ATPases). In contrast, the transient Ca2+ response induced by oxytocin was unaffected by ryanodine. Moreover, caffeine failed to induce a rise in [Ca2+]i but reduced the oxytocin-induced transient Ca2+ response. The later sustained rise in [Ca2+]i produced by oxytocin was due to the entry of Ca2+ into the cell as it was suppressed in external Ca2+-free solution. The Ca2+ entry pathway is permeable to Mn2+ ions, in contrast to that described in various vascular and visceral smooth muscle cells. Oxytocin-induced Ca2+ release is blocked by the oxytocin antagonist d(CH2)5[Tyr(Me)2,Thr4,Tyr-NH 2 9 ]OVT. The prolonged increase in [Ca2+]i after oxytocin removal is rapidly terminated by addition of the oxytocin antagonist suggesting that oxytocin dissociation from its receptor is very slow. The oxytocin stimulation of [Ca2+]i was insensitive to incubation with pertussis toxin, and blocked by a pipette solution containing anti-αq/α11 antibody. These data show that myometrial cells possess an unique heparin-sensitive and thapsigargin-sensitive store that can be mobilized by activation of oxytocin receptors which couples with a Gq/G11-protein to activate phospholipase C.

Key words

Free cytosolic calcium Fura-2 Oxytocin G-protein Myometrium 

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Copyright information

© Springer-Verlag 1994

Authors and Affiliations

  • S. Arnaudeau
    • 1
  • N. Leprêtre
    • 1
  • J. Mironneau
    • 1
  1. 1.Laboratoire de Physiologie Cellulaire et Pharmacologie Moléculaire, URA CNRS 1489Université de Bordeaux IIBordeauxFrance

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