URIDINE NUCLEOTIDE SELECTIVITY OF 3 PHOSPHOLIPASE C-ACTIVATING P-2 RECEPTORS - IDENTIFICATION OF A UDP-SELECTIVE, A UTP-SELECTIVE, AND AN ATP-SPECIFIC AND UTP-SPECIFIC RECEPTOR

Observation that the G protein-coupled P-2U receptor (P2Y(2) receptor) is activated by UTP as well as ATP provided the first indication that a class of uridine nucleotide-responsive receptors might exist. This hypothesis was confirmed by our identification of a uridine nucleotide -specific receptor on C6-2B rat glioma cells and by the recent cloning of two uridine nucleotide-responsive receptors, the P2Y(6) receptor [ J. Biol. Chem. 270:26152-26158 (1995)] and the P2Y(4) receptor [J. Bio l. Chem. 270:30849-30852 (1995) and J. Biol. Chem. 270:30845-30848 (19 95)]. The relative nucleotide selectivities of these uridine nucleotid e-activated receptors have not been established. Therefore, we cloned and expressed the P2Y(6) and P2Y(4) receptors in 1321N1 human astrocyt oma cells and compared their relative selectivities for UDP, UTP, and other uridine and adenine nucleotides with that of the P2Y(2) receptor expressed in the same cells. These comparisons were made by measuring inositol phosphate accumulation under conditions in which the initial purity and stability of agonists were rigidly ensured and quantitativ ely assessed. The data indicate that the P2Y(2) receptor is activated with similar potencies by ATP and UTP but not by ADP or UDP; the P2Y(6 ) receptor is activated most potently by UDP but weakly by UTP, ATP, a nd ADP; and the P2Y(4) receptor is activated most potently by UTP, les s potently by ATP, and not at all by nucleotide diphosphates. Furtherm ore, the P2Y(6) receptor, which displays a uridine nucleotide selectiv ity essentially identical to that of the uridine nucleotide-specific r eceptor in C6-2B cells, was shown to be natively expressed in C6-2B ce lls and to account for the uridine nucleotide responses originally ide ntified in these cells. These results define the uridine nucleotide se lectivity of three phospholipase C-linked receptors: a receptor that i s selectively activated by UDP (P2Y(6) receptor), selectively activate d by UTP (P2Y(4) receptor), and activated by UTP and ATP but not by di phosphate nucleotides (P2Y(2) receptor).