Purinergic Receptor Expression and Activation in First Trimester and Term Human Placenta

Intracellular calcium concentration ([Ca²⁺]_i) is an important signalling molecule in the human placenta and regulation of [Ca²⁺]_i must be tightly controlled to ensure normal cell function and in order to meet the changing demand for calcium with increased fetal growth over gestation. Little is known about the receptors and mechanisms involved in intracellular calcium signalling in the human placenta but in isolated cytotrophoblast cells members of the P2 purinergic receptor family have been shown to mediate an ATP-stimulated rise in [Ca²⁺]_i. In this study we examined activation and expression of several of the purinergic receptor subtypes in human placental villous fragments at two stages of gestation, first trimester and term. We demonstrate mRNA and protein expression of the P2X₄, P2X₇ and P2Y₂ subtypes but found no evidence of P2Y₄ protein in the placenta. Using fluorescent calcium imaging we demonstrate that 300 μM ATP, 450 μM UTP and 300 μM BzATP significantly elevate [Ca²⁺]_i in villous fragments with a significant increase in agonist-induced response seen in the term compared to the first trimester fragments (ATP, P < 0.0001; UTP, P = 0.018; BzATP, P = 0.015). The roles of the purinergic receptors within the human placenta are not known but it seems likely for this study that calcium handling through these receptors is altered with advancing gestation. This may be due to the need to meet increased fetal Ca²⁺ requirements due to growth or as a secondary function to alterations in placental [Ca²⁺]_i signalling.