ATP evokes Ca2+ signals in cultured foetal human cortical astrocytes entirely through G protein-coupled P2Y receptors

Abstract

Extracellular ATP plays important roles in coordinating the activities of astrocytes and neurons, and aberrant signalling is associated with neurodegenerative diseases. In rodents, ATP stimulates opening of Ca$^{2+}$-permeable channels formed by P2X receptor subunits in the plasma membrane. It is widely assumed, but not verified, that P2X receptors also evoke Ca$^{2+}$ signals in human astrocytes. Here we directly assess this hypothesis. We showed that cultured foetal cortical human astrocytes express mRNA for several P2X receptor subunits (P2X$_4$, P2X$_5$, P2X$_6$) and G-protein-coupled P2Y receptors (P2Y$_1$, P2Y$_2$, P2Y$_6$, P2Y$_{11}$). In these astrocytes, ATP stimulated Ca$^{2+}$ release from intracellular stores through IP$_3$ receptors and store-operated Ca$^{2+}$ entry. These responses were entirely mediated by P2Y$_1$ and P2Y$_2$ receptors. Agonists of P2X receptors did not evoke Ca$^{2+}$ signals, and nor did ATP when Ca$^{2+}$ release from intracellular stores and store-operated $^{}$Ca$^{}$2+ entry were inhibited. We conclude that ATP-evoked Ca$^{2+}$ signals in cultured human foetal astrocytes are entirely mediated by P2Y$_1$ and P2Y$_2$ receptors, with no contribution from P2X receptors.