P2Y receptors: focus on structural, pharmacological and functional aspects in the brain

Purine and pyrimidine nucleotides have been identified as potent extracellular signalling molecules, acting at two classes of cell surface receptors, ionotropic P2X and metabotropic P2Y receptor (-R) types. Hitherto eight subtypes of the P2Y-R family have been cloned from mammalian species that exhibit sensitivity to the adenine nucleotides ATP/ADP (P2Y(1,11,12,13)), the uracil nucleotides UTP/UDP (P2Y(2,4,6) or UDP-glucose in the case of P2Y(14)) or both adenine and uracil nucleotides (P2Y(2)). The P2Y-Rs are G protein-coupled receptors activating phospholipase C via Galpha(q/11) protein and stimulating or inhibiting adenylyl cyclase via Galpha(s) and Galpha (i/o) proteins, respectively. These receptors may activate distinct signalling cascades. Although classical models predict that P2Y-Rs exist in the cell membrane as monomers, homo- or heterodimeric assemblies may be generated. Interactions with certain ion channels or ligand-gated receptors as well as the co-localization of several receptor subtypes in the same cell provide the basis for a high functional diversity. The proteins for various P2Y-Rs are expressed early in the embryonic brain and are broadly distributed on both, neurons and astroglial cells. P2Y-R involvement in the regulation of normal physiological processes on the cellular level or in vivo, such as modulation of transmitter release, generation of astroglial Ca(2+) waves, in diverse effects on behavioural functions and in the etiopathology of neurodegenerative diseases, are discussed and own data are presented. However, the exact understanding of the role of individual P2Y-R subtypes is still limited. Concerning the potentially important functions of P2Y-Rs, there is a strong need to develop stable, lipophilic and subtype-selective P2Y-R ligands, which may open new therapeutic strategies.