HETEROGENEITY OF P-2U-PURINERGIC AND P-2Y-PURINERGIC RECEPTOR REGULATION OF PHOSPHOLIPASES IN MDCK CELLS

We have characterized the signaling pathways of purinergic receptors p resent on the renal epithelial cell line, Madin-Darby canine kidney (M DCK, D-1 subclone). Several lines of evidence are consistent with the conclusion that coexisting P-2u and P-2y receptors release arachidonic acid and metabolites (AA) from MDCK-D-1 cells: 1) relative potencies of nucleotide analogues, 2) blockade of P-2y agonist- but not P-2u ago nist-mediated release by suramin, and 3) additivity by 2-methylthio-AT P and UTP. Differences exist between the signaling pathways of the two receptors: pertussis toxin treatment partially inhibits P-2u- but not P-2y-mediated AA release, and P-2y (but not P-2u) receptors appear to stimulate D-myo-inositol 1,4,5-trisphosphate production. P-2u-recepto r occupancy results in both homologous and heterologous desensitizatio n; P-2y-receptor occupancy elicits only homologous desensitization. Bo th receptors stimulate phosphatidylcholine hydrolysis via phospholipas e C activation. However, AA release appears to result from phospholipi d deacylation by phospholipase A(2) activation, rather than from alter nate pathways that may include PLC activation. These results demonstra te for the first time that two subtypes of P-2-purinergic receptors, P -2u and P-2y receptors, coexist on a single renal epithelium cell type and that these two receptor subtypes can promote AA release, probably via activation of PLA(2).