BINDING AND FUNCTIONS OF EXTRACELLULAR ATP IN CULTURED CEREBELLAR GRANULE NEURONS

Selected purinoceptor modulators were previously shown to prevent glut amate-evoked cytotoxicity in cerebellar granule neurons. In the same c ellular system, we now identify and characterize the presence of P-2 r eceptors. The binding of [H-3]ATP to membranes of cerebellar granule n eurons grows monotonically as a function of neuronal differentiation, is saturable and reaches steady state within 6 min. Scatchard plot of the equilibrium saturation data is curvilinear with a K-d value of 28 nM and a B-max value of 87 pmol/ mg of protein for the high affinity b inding sites and a K-d value of 1.5 mu M and B-max value of 1.2 nmol/m g of protein, for the more numerous low affinity binding sites. We als o show that extracellular ATP increases the release, but not the uptak e, of [H-3]D-aspartate and that it furthermore potentiates the release of [H-3]D-aspartate evoked by glutamate and KCl. ATP itself is releas ed by cerebellar granule cultures and such release grows monotonically as a function of neuronal differentiation. These data are consistent with the role that ATP is believed to play as a cotransmitter for the central nervous system. (C) 1996 Academic Press. Inc.