Adenosine triphosphate (ATP) is stored as lysosomal vesicles in marginal cells of the stria vascular in neonatal rats, but the mechanisms of ATP release are unclear. Primary cultures of marginal cells from 1-day-old Sprague–Dawley rats were established. P2Y 2 receptor and inositol 1,4,5-trisphosphate (IP3) receptor were immunolabelled in marginal cells of the stria vascular. We found that 30 μM ATP and 30 μM uridine triphosphate (UTP) evoked comparable significant increases in the intracellular Ca 2+ concentration ([Ca 2+ ] i ) in the absence of extracellular Ca 2+ , whereas the response was suppressed by 100 μM suramin, 10 μM 1-(6-(17β-3-methoxyester-1,3,5(10)-trien-17-yl)amino)-hexyl)-1H-pyrrole-2,5-dione(U-73122), 100 μM 2-aminoethoxydiphenyl borate (2-APB) and 5 μM thapsigargin (TG), thus indicating that ATP coupled with the P2Y 2 R-PLC-IP3 pathway to evoke Ca 2+ release from the endoplasmic reticulum (ER). Incubation with 200 μM Gly-Phe-β-naphthylamide (GPN) selectively disrupted lysosomes and caused significant increases in [Ca 2+ ] I ; this effect was partly inhibited by P2Y 2 R-PLC-IP3 pathway antagonists. After pre-treatment with 5 μM TG, [Ca 2+ ] i was significantly lower than that after treatment with P2Y 2 R-PLC-IP3 pathway antagonists under the same conditions, thus indicating that lysosomal Ca 2+ triggers Ca 2+ release from ER Ca 2+ stores. Baseline [Ca 2+ ] i declined after treatment with the Ca 2+ chelator 50 μM bis-(aminophenolxy) ethane- N , N , N ʹ, N ʹ-tetra-acetic acid acetoxyme-thyl ester (BAPTA-AM) and 4 IU/ml apyrase. 30 μM ATP decrease of the number of quinacrine-positive vesicles via lysosome exocytosis, whereas the number of lysosomes did not change. However, lysosome exocytosis was significantly suppressed by pre-treatment with 5 μM vacuolin-1. Release of ATP and β-hexosaminidase both increased after treatment with 200 μM GPN and 5 μM TG, but decreased after incubation with 50 μM BAPTA-AM, 4 IU/ml apyrase and 5 μM vacuolin-1. We suggest that ATP triggers Ca 2+ release from the ER, thereby contributing to secretion of lysosomal ATP via lysosomal exocytosis. Lysosomal stored Ca 2+ triggers Ca 2+ release from the ER directly though the IP3 receptors, and lysosomal ATP evokes Ca 2+ signals indirectly via the P2Y 2 R-PLC-IP3 pathway.
Xiao-Wei Gu,Zi-Cong Chen,Zhen-Shan Yang,Yan Yang,Ya-Ping Yan,Yue-Fang Liu,Ji-Min Pan,Ren-Wei Su,Zeng-Ming Yang
Embryo implantation involves a sterile inflammatory reaction that is required for the invasion of the blastocyst into the decidua. Adenosine triphosphate (ATP) released from stressed or injured cells acts as an important signaling molecule to regulate many key physiological events, including sterile inflammation. We found that the amount of ATP in the uterine luminal fluid of mice increased during the peri-implantation period, and this depended on the presence of an embryo. We further showed that the release of ATP from receptive epithelial cells was likely stimulated by lactate released from the blastocyst through connexin hemichannels. The ATP receptor P2y2 was present on uterine epithelial cells during the preimplantation period and increased in the stromal cells during the time at which decidualization began. Pharmacological inhibition of P2y2 compromised decidualization and implantation. ATP-P2y2 signaling stimulated the phosphorylation of Stat3 in uterine luminal epithelial cells and the expression of early growth response 1 ( Egr1 ) and prostaglandin-endoperoxide synthase 2 ( Ptgs2, also known as Cox-2 ), all of which are required for decidualization and/or implantation, in stromal cells. Short exposure to high concentrations of ATP promoted decidualization of primary stromal cells, but longer exposures or lower ATP concentrations did not. The expression of genes encoding ATP-degrading ectonucleotidases increased in the decidua during the peri-implantation period, suggesting that they may limit the duration of the ATP signal. Together, our results indicate that the blastocyst-induced release of ATP from uterine epithelial cells during the peri-implantation period may be important for the initiation of stromal cell decidualization.
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