Synergistic effects of ATP on oxytocin-induced intracellular Ca2+ response in mouse mammary myoepithelial cells.
An increase in intracellular Ca2+ ([Ca2+]i) is essential for mammary myoepithelial cells to contract, leading to milk ejection during lactation. In this study, the intracellular signaling leading to the increase in [Ca2+]i in cultured myoepithelial cells from mouse lactating mammary glands was investigated using fura-2 fluorescence ratiometry. [Ca2+]i increased in cultured myoepithelial cells in response to either oxytocin (1 nM) or ATP (10 microM), and the cells then contracted. These [Ca2+]i responses were diminished by treatment with an inhibitor of phospholipase C (> or = 1 microM U73122). Intracellular application of inositol 1,4,5-trisphosphate (IP3: 10 or 100 microM) increased [Ca2+]i. Pretreatment with pertussis toxin (PTX: 0.1 or 1 microgram/ml) inhibited the [Ca2+]i response to ATP, but had less of an effect on the response to oxytocin. These results indicate that oxytocin and purinergic receptors are coupled to PTX-insensitive and PTX-sensitive G proteins, respectively, and that their activation leads to the increase in [Ca2+]i through the release of Ca2+ from IP3-sensitive intracellular stores via the inositol-phospholipid signaling pathway. Furthermore, we found that the [Ca2+]i responses to oxytocin at physiological doses (0.01-0.1 nM) were augmented in the presence of a sub-responsive dose of ATP (1 microM). The activation of purinergic receptors may facilitate myoepithelial cell contraction in milk-ejection responses.
Nakano
H
H
Department of Animal Reproduction, National Institute of Animal Industry, PO Box 5, Tsukuba-norindanchi, Ibaraki, 305-0901, Japan. nakanoh@niai.affrc.go.jp
Furuya
K
K
Yamagishi
S
S
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000378:metabolism; D004963:Estrenes / Q000494:pharmacology; D005260:Female; D016257:Fura-2; D019204:GTP-Binding Proteins / Q000378:metabolism; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D007774:Lactation; D008321:Mammary Glands, Animal / Q000378:metabolism*; D051379:Mice; D008813:Mice, Inbred ICR; D010121:Oxytocin / Q000494:pharmacology*; D037342:Pertussis Toxin; D011760:Pyrrolidinones / Q000494:pharmacology; D015398:Signal Transduction; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D004791:Enzyme Inhibitors; D004963:Estrenes; D011760:Pyrrolidinones; D010566:Virulence Factors, Bordetella; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; D010121:Oxytocin; D015544:Inositol 1,4,5-Trisphosphate; D000255:Adenosine Triphosphate; D037342:Pertussis Toxin; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins; D002118:Calcium; D016257:Fura-2