Oxytocin mobilizes calcium from a unique heparin-sensitive and thapsigargin-sensitive store in single myometrial cells from pregnant rats.
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 Ca(2+)-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 Ca(2+)-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-NH2(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.(ABSTRACT TRUNCATED AT 250 WORDS)
Arnaudeau
S
S
Laboratoire de Physiologie Cellulaire et Pharmacologie Moléculaire, URA CNRS 1489, Université de Bordeaux II, France.
Leprêtre
N
N
Mironneau
J
J
D000109:Acetylcholine / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D005260:Female; D019204:GTP-Binding Proteins / Q000378:metabolism; D006493:Heparin / Q000494:pharmacology*; D015151:Immunoblotting; D008345:Manganese / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D009215:Myometrium / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010121:Oxytocin / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D011247:Pregnancy; D051381:Rats; D017208:Rats, Wistar; D018045:Receptors, Oxytocin / Q000187:drug effects; D012433:Ryanodine / Q000494:pharmacology; D013729:Terpenes / Q000494:pharmacology*; D019284:Thapsigargin
D000889:Anti-Arrhythmia Agents; D002121:Calcium Channel Blockers; D018045:Receptors, Oxytocin; D013729:Terpenes; D012433:Ryanodine; D008345:Manganese; D010121:Oxytocin; D019284:Thapsigargin; D006493:Heparin; D019204:GTP-Binding Proteins; D000109:Acetylcholine; D002118:Calcium