Two distinct P2Y receptors are involved in purine- and pyrimidine-evoked Ca2+ elevation in mammalian brain astrocytic cultures

ATP and 2-methyl-thio-ATP (2-Me-SATP) increase cytosolic calcium concentrat ions ([Ca2+](i)) in rat striatal astrocytes (Centemeri et al. (1997) Br J P harmacol 121:1700-1706). The aim of the present study was to: (1) character ize pyrimidine-induced [Ca2+](i) increases in the same experimental system, and (2) try to identify the multiple P2Y receptor subtypes mediating Ca2mobilization. UDP and UTP triggered a concentration-dependent [Ca2+](i) ele vation (EC(50)s = 0.58 muM +/- 0.4 and 31 muM +/- 6, respectively). Pyrimid ine-evoked [Ca2+](i) elevation was solely due to mobilization from intracel lular stores, because: (1) removing calcium from extracellular medium or (2 ) blocking its influx with Ni2+ did not modify UTP responses; (3) the store -depleting agent thapsigargin completely abolished UTP-evoked [Ca2+](i) inc rements. Guanosine-5'-O-(2-thiodiphosphate) partially inhibited the UTP res ponse, whereas pertussis toxin (PTx) had no effect. The phospholipase C inh ibitor U-73122 significantly reduced the UTP-evoked [Ca2+](i) rise. Compute r-assisted analysis indicated that the UTP and UDP responses are mediated b y a single receptor, while ATP and 2-Me-SATP interact with two distinct rec eptors. The selective P2Y(1) receptor antagonist MRS2179 abolished the ATP higher potency component. Sequential challenges with the same nucleotides r esulted in almost complete homologous desensitization. Pre-exposure to UTP lowered the subsequent responses to either ATP or 2-Me-SATP. Maximally acti ve concentrations of UTP and ATP were not additive. In conclusion, [Ca2+](i ) elevation in astrocytes by purines and pyrimidines is mediated by two dis tinct P2Y receptors, likely the P2Y(1) and P2Y(6), subtypes. Drug Dev. Res. 52:122-132, 2001. (C) 2001 Wiley-Liss, Inc.