Binding of 5′- O-(2-thiodiphosphate) to rat brain membranes is prevented by diadenosine tetraphosphate and correlates with ecto-nucleotide pyrophosphatase phosphodiesterase 1 (NPP1) activity

The distribution of binding sites for [ 35S]5′- O-(2-thiodiphosphate) ([ 35S]ADPβS), a radioligand of P2Y 1,12,13 receptors, and of ecto-nucleotide pyrophosphatase phosphodiesterase activity were analyzed in the rat forebrain. Binding sites for the radilogand are widespreadly distributed in the rat forebrain, showing the highest density in hypothalamus. K d values were in the range 1–2 nM. Diadenosine tetraphosphate (Ap 4A) and diethenoadenosine tetraphosphate, ɛ-(Ap 4A), displaced the radioligand, indicating dinucleotide binding to ADPβS-recognizing P2Y receptors. Activity ecto-nucleotide pyrophosphatase phosphodiesterase 1 (NPP1), able to hydrolyze Ap 4A and other diadenosine polyphosphates, is also widely distributed through the rat forebrain, with the highest activity in hypothalamus. These results suggests that Ap 4A signalling mediated by P2Y 1,12,13 receptors and enzymatically regulated by NPP1 activity may be particularly important in hypothalamus and add new support for neurotransmitter/neuromodulatory functions of diadenosine polyphosphates in brain.