Identification of a uridine nucleotide-selective G-protein-linked receptor that activates phospholipase C.

Incubation of C6-2B rat glioma cells with UDP or UTP resulted in a time-and concentration-dependent increase in the accumulation of inositol phosphates. In contrast, ATP, ADP, and analogs of these nucleotides known to be effective agonists at Pzv-, Pm-, P,,-, P,,-, and P,,-purinergic receptors all had no effect on inositol phosphate levels in C6-2B cells. Pyrimidine nucleotides stimulated inositol phosphate accumulation with an order of potency of UDP > 5-BrUTP > UTP > dTDP > UDP glucose. values for UDP, 5-BrUTP, and UTP were 2.3 * 0.5,9 * 3, and 57 10 m, respectively. A similar uridine nucleotide selectivity was observed for arachidonic acid release presumably occurring as a consequence of activation of phospholipase 4. Cross-desensitization and additivity experiments indicated that UDP and UTP interact with the same population of receptors. The effect of uridine nucleotides on inositol phosphate accumulation was inhibited markedly by pretreatment of cells with pertussis toxin. UDP also caused a guanine nucleotide-dependent increase in inositol lipid hydrolysis in streptolysin-0-permeabilized cells. Taken together these results describe the existence of a novel uridine nucleotide receptor that is not activated by adenine nucleotides. This receptor is pharmacologically distinct from the previously described P2"-and other P,-purinergic receptors, and likely is a member of a new class of receptors for extracellular nucleotides. Extracellular release of adenine nucleotides from neurons, platelets, and other tissues results in activation of a broad range of physiological responses (1, 2). Considerable progress has been made in the last decade in the pharmacological delineation of the cell surface receptors that are activated by extracellular ATP and ADP. These P,-purinergic receptors include the P, The one exception to the adenine nucleotide selectivity of these receptors is the so-called P,,purinergic receptor, which is not only activated by ATP and ATPyS,' but also is stimulated by the pyrimidine, UTP (4-8).