P2 receptors in cerebellar neurons: Molecular diversity of ionotropic ATP receptors in purkinje cells

ATP is now recognized as a fast neurotransmitter after the demonstration of synaptic transmission mediated by ATP in the medial habenula, locus coeruleus, spinal cord, and hippocampus. We focused on the postnatal rat cerebellum as a model territory and studied the role of ATP neurotransmission using cultured cells. Cerebellar Purkinje neurons in culture express ionotropic P2X receptors. We have shown that Ca²⁺ signals mediated by ATP in Purkinje cells present pharmacological profile characteristics of ATP receptors formed by P2X₂ subunits. However, the complete range of known P2X subunits are expressed in the cerebellum. With the aid of the RT-PCR technique we identified mRNA for P2X_1-4 and P2X₆ subunits in the rat cerebellum during the first postnatal week. These results have been confirmed by Southern blotting of PCR products using selective P2X probes. This opens the question of the relative contribution of each subunit to functional channels. Immunocytochemical labeling using anti-P2X antibodies reveal that several P2X subunits colocalize to the same Purkinje cell. This raises the possibility of extensive heterooligomerization of P2X subunits. Patch-clamping of Purkinje cells in culture indicates the presence of two subpopulations of ATP receptors: a fast and rapidly desensitizing receptor and a nondesensitizing receptor with slower kinetics. Our results suggest that both receptors may be formed by co-assembly of dissimilar P2X subunits.