Molecular cloning and characterization of rat P2Y4 nucleotide receptor

An intronless open reading frame encoding a protein (361aa in length) was isolated from a rat genomic library probed with a DNA fragment from rat heart. This protein showed 83% sequence identity with the human P2Y(4) (hP2Y(4)) receptor and represents a homologue of the human pyrimidinoceptor. However, the rP2Y(4) receptor is not selective for uridine nucleotides and, instead, shows an agonist potency order of ITP = ATP = ADP(pure) = UTP = ATP gamma S = 2-MeSATP = Ap(4)A > UDP(pure). ADP, ATP gamma S, 2-MeSATP and UDP are partial agonists. Thus, in terms of agonist profile, rP2Y(4) is more like the P2U receptor subtype. The rP2Y(4) receptor was reversibly antagonized by Reactive blue 2 but not by suramin which, otherwise, inhibits the hP2Y(2) receptor (a known P2U receptor). Thus, rP2Y(4) and the P2Y(2) subtype appear to be structurally distinct forms of the P2U receptor (where ATP and UTP are equi-active) but can be distinguished as suramin-insensitive and suramin-sensitive P2U receptors, respectively.