Arachidonic acid (AA) plays important physiological or pathophysiological roles. Here, we show in Cultured rat astrocytes that: (i) endothelin-1 or thapsigargin (Tg) induces store-depleted activated Ca2+ entry (CCE), which is inhibited by 2-aminoethoxydiphenyl borane (2-APB) or La3+; (ii) AA (10 μ M) and other unsaturated fatty acids (8,11,14-eicosatrienoic acid and γ-linoleic acid) have an initial inhibitory effect on the CCE, due to AA- or fatty acid-induced internal acid load; (iii) after full activation of CCE, AA induces a further Ca2+ influx, which is not inhibited by 2-APB or La3+, indicating that AA activates a second Ca2+ entry pathway, which coexists with CCE; and (iv) Tg or AA activates two independent and co-existing non-selective cation channels and the Tg-induced currents are initially inhibited by addition of AA or weak acids. A possible pathophysiological effect of the AA-induced [Ca](i) overload is to cause delayed cell death in astrocytes. © 2005 Elsevier Inc. All rights reserved.