P2X₂and P2Y₁immunofluorescence in rat neostriatal medium-spiny projection neurones and cholinergic interneurones is not linked to respective purinergic receptor function

1 The presence of ionotropic P2X receptors, targets of ATP in fast synaptic transmission, as well as metabotropic P2Y receptors, known to activate K+ currents in cultured neostriatal neurones, was investigated in medium-spiny neurones and cholinergic interneurones contained in neostriatal brain slices from 5 - 26-day-old rats. 2 In these cells, adenosine-5'-triphosphate (ATP) ( 100 - 1000 muM), 2-methylthioadenosine-5'-triphosphate (2MeSATP), alpha,beta-methyleneadenosine-5'-triphosphate (alpha,betameATP, 30 - 300 muM, each) and adenosine-5'-O-(3-thiotriphosphate (ATPgammaS) ( 100 muM) failed to evoke P2X receptor currents even when 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 0.1 muM), apyrase (10 U ml(-1)) or intracellular Cs+ was used to prevent occluding effects of the ATP breakdown product adenosine, desensitisation of P2X receptors by endogenous ATP and an interference with the activation of K+ channels, respectively. P2X receptor agonists were also ineffective in outside-out patches withdrawn from the brain slice tissue. Muscimol (10 muM) evoked GABA(A) receptor-mediated currents under all these conditions. 3 When used as a control, locus coeruleus neurones responded with P2X receptor-mediated currents to ATP ( 300 mM), 2MeSATP and a, bmeATP ( 100 mM, each). 4 ATP and adenosine-5'-diphosphate (ADP) ( 100 muM, each) did not activate K+ currents in the neostriatal neurones. 5 Despite the observed lack of function, P2X(2) and P2Y(1) immunofluorescence was found in roughly 50% of the medium-spiny neurones and cholinergic interneurones. 6 A role of ATP in synaptic transmission to striatal medium-spiny neurones and cholinergic interneurones appears unlikely, however, the otherwise silent P2X and P2Y receptors may gain functionality under certain yet unknown conditions.