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)
Laboratoire de Physiologie Cellulaire et Pharmacologie Moléculaire, URA CNRS 1489, Université de Bordeaux II, France.
S
S
Arnaudeau
N
N
Leprêtre
J
J
Mironneau
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