P2Y PURINOCEPTORS IN GASTRIC GLAND PLASMA-MEMBRANES

This autoradiographic study of sections of the rabbit stomach fundus l abelled with [S-35]dATP alpha S, a radioligand for P2Y purinoceptors, has demonstrated a discrete pattern of distribution of the binding sit es, i.e., the specific binding was only over the mucosa, but not over the muscular layer. Radioligand binding assays carried out on gastric gland plasma membranes showed that the binding process was saturable a nd a high density of a homogeneous population of binding sites was obs erved. These binding sites presented high affinity with a value of K-d = 4.1 +/- 0.8 nM and the maximum density of the binding sites was 16. 8 +/- 1.6 pmol/mg protein. The displacement by purinoceptor ligands sh owed the following order of potency: ATP=2-methylthio ATP much greater than alpha,beta-methylene ATP much greater than adenosine. Ne ther UT P nor pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS) wer e able to displace the binding. The data support the presence of P2Y p urinceptors in rabbit gastric glands.