P2X receptors are ATP-gated ion channels that play a role in intracellular calcium signaling. Not required for the purinergic response to extracellular nucleotides. Not essential for osmoregulation. Inward currents evoked by intracellular ATP. ATP analog beta, gamma-imido-ATP is a weak partial agonist of p2xE. Exclusively selective for ATP over other nucleotides. Insensitive to copper and P2 receptor antagonists PPADS and suramin but strongly inhibited by sodium ions. More permeable to ammonium than either sodium or potassium ions and less permeable to choline. Permeable to calcium ions, but not chloride. Ligand binding domain within the lumen of the vacuole. Response to extracellular ATP remains the same in p2xE null strains. Null cells are still capable of osmoregulation and do not show any noticeable differences in their sensitivity to hypotonic conditions. Quintuple p2xA/p2xB/p2xC/p2xD/p2xE null cells displayed slight delay in their osmoregulatory response, but are still capable of regulating their cell volume in water. Extracellular purinergic response to ATP persists in the quintuple null cells with no alteration in the kinetics of the response, but the magnitude of the response is lower. Responses to the calmodulin antagonist calmidazolium are reduced and intracellular calcium signaling is disrupted in quintuple null cells. The presence of copper prevented both wild type and quintuple null cells from undergoing an osmoregulatory decrease in cell volume. No obvious morphological phenotype was apparent in the p2xE or quintuple p2x null strains. The quintuple p2x null strains grow slightly slower than wild type in shaking axenic cultures. Belongs to the P2X receptor family.