P2X receptors are ligand-gated ion channels that play a role in intracellular calcium signaling. ATP does not evoke inward currents in p2xC. Not essential for osmoregulation. Ligand binding domain within the lumen of the vacuole. 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 and p2xC single null strains 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 p2xC or quintuple p2x null strains. The quintuple null strain however did grow slightly slower than wild type in shaking axenic cultures. Belongs to the P2X receptor family.