Slow desensitization of the human P2Y(6) receptor

The P2Y(6) receptor is a recently cloned P-2 receptor which displays a high sensitivity for diphosphonucleotides. In 1321N1 astrocytoma cells stably expressing this receptor, UDP induced a slow and sustained accumulation of inositol trisphosphate via a pertussis toxin-insensitive G-protein: the maximal level was only reached after 15 min and a significant response was maintained for at least 3 h. A full second response to UDP was obtained after the first 45-min stimulation but was lost after 165 min. This slow and sustained time-course and the lack of desensitization was reproduced with ADP. UTP was unable to restimulate the P2Y(4) receptor, another recently cloned P-2 receptor with a preference for UTP, after the first 5-min stimulation. The P2Y(4) receptor is thus rapidly desensitized whereas desensitization of the P2Y(6) receptor is delayed. The rank order of potency of various diphosphonucleotides at the P2Y(6) receptor was: UDP > TDP > IDP > GDP > ADP >> CDP. The activity of three non-specific antagonists of P-2 receptors was characterized by the following rank order of potency: reactive blue 2 > pyridoxal-phosphate-6-azophenyl-2',4'-disulphonic acid (PPADS)> suramin. In conclusion, the most impressive features of the human P2Y(6) receptor revealed by this study are the slow and sustained time-course of its activation and its. high resistance to desensitization. (C) 1997 Elsevier Science B.V.