The majority of mammalian cells demonstrate regulatory volume decrease (RVD) following swelling caused by hypoosmotic exposure. A critical signal initiating RVD is activation of nucleotide receptors by ATP. Elevated extracellular ATP in response to cytotoxic cell swelling during pathological conditions also may initiate loss of taurine and other intracellular osmolytes via anion channels. This study characterizes neuronal ATP-activated anion current and explores its role in net loss of amino acid osmolytes. To isolate anion currents, we used CsCl as the major electrolyte in patch electrode and bath solutions and blocked residual cation currents with NiCl₂ and tetraethyl ammonium. Anion currents were activated by extracellular ATP with a K_m of 70 µM and increased over four-fold during several minutes of ATP exposure, reaching a maximum after 9.0 min (SD 4.2). The currents were blocked by inhibitors of nucleotide receptors and volume-regulated anion channels (VRAC). Currents showed outward rectification and inactivation at highly depolarizing membrane potentials, characteristics of swelling-activated anion currents. P2X agonists failed to activate the anion current and an inhibitor of P2X receptors did not block the effect of ATP. Furthermore, current activation was observed with extracellular ADP and MeS-ADP, a P2Y₁ receptor-specific agonist. Much less current activation was observed with extracellular UTP suggesting the response is mediated predominantly by P2Y₁ receptors. ATP caused a dose-dependent loss of taurine and alanine which could be blocked by inhibitors of VRAC. ATP did not inhibit the taurine uptake transporter. Thus, extracellular ATP triggers a loss of intracellular organic osmolytes via activation of anion channels. This mechanism may facilitate neuronal volume homeostasis during cytotoxic edema.