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1 Division of Human Development, St Mary's Hospital, The Medical School, University of Manchester, Manchester, United Kingdom; Department of Obstetrics & Gynecology, University of Cincinnati, Cincinnati, OH, USA
2 Division of Human Development, St Mary's Hospital, The Medical School, University of Manchester, Manchester, United Kingdom
3 School of Biological Sciences, University of Manchester, Manchester, United Kingdom
4 Division of Development, Growth and Function, Rowett Research Institute, Aberdeen, United Kingdom
* To whom correspondence should be addressed. E-mail: susan.greenwood{at}manchester.ac.uk.
Appropriate regulation of ion transport by the human placental syncytiotrophoblast is important for fetal growth throughout pregnancy. In non-placental tissues, ion transport can be modulated by extracellular nucleotides which raise intracellular calcium ([Ca2+]i) via activation of purinergic receptors. Here we test the hypothesis that purinergic receptors are expressed by human placental cytotrophoblast cells and that their activation by extracellular nucleotides modulates ion (K+) efflux and ([Ca2+]i). The P2X/P2Y receptor agonists 5BrUTP, ADP, ATP, BzATP and UTP stimulated 86Rb (tracer for K+) efflux from cultured cytotrophoblast cells at early (mononuclear) or later (multinucleate syncytiotrophoblast-like) stages of differentiation, with ATP and UTP being particularly potent. 2meSATP and UDP elevated 86Rb efflux only from multinucleate cells. All agonists caused a significant peak and plateau increase in [Ca2+]i although the magnitude of the responses was variable. The effect of BzATP, UTP and UDP in multinucleated cells was unaffected, and that of ATP partially inhibited, by the removal of extracellular Ca2+, implicating P2Y receptor activation. Messenger RNA encoding P2X1,2,4 and P2X7, and P2Y1,2,4,6 and P2Y11 was identified in mono- and multinucleated cells, whereas P2X3 and P2X5 mRNAs were absent from all samples. Western blotting revealed P2X4, P2X7, P2Y2 and P2Y6 protein in cytotrophoblast cells but P2Y4 was not detected. Based on published agonist selectivity, the data indicate the presence of functionally active P2X4, P2X7, P2Y2 and P2Y6 receptors in cytotrophoblast cells. We propose that activation of these receptors, and subsequent elevation of [Ca2+]i, modulates syncytiotrophoblast homeostasis and /or maternofetal ion exchange in response to extracellular nucleotides.
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