P2RX4 and astrocytoma (excluding glioblastoma): In this drug screening, ambroxol (Appendix Fig S4A) was identified, as it showed a significant inhibition of ATP‐induced calcium influx in 1321N1 astrocytoma cells transfected with the human P2X2 receptor (IC50: 5.69 ± 1.06 μM), but not in cells transfected with P2X1, P2X3, P2X4, or P2X7 receptors (Fig EV4A).