Stimulation of Xenopus P2Y1 receptor activates CFTR in A6 cells

Nucleotide binding to purinergic P2Y receptors contributes to the regulation of a variety of physiological functions in renal epithelial cells. Here, we investigate the regulatory mechanism of the P2Y1 receptor agonist 2-methylthioadenosine diphosphate (2-MeSADP) on Cl^– transport in A6 cells, a commonly used model of the distal section of the Xenopus laevisnephron. Protein and mRNA expression analysis together with functional measurements demonstrated the basolateral location of the Xenopus P2Y1 receptor. 2-MeSADP increased intracellular [Ca²⁺] and cAMP and Cl^– efflux, responses that were all inhibited by the specific P2Y1 receptor antagonist MRS 2179. Cl^–efflux was also inhibited by the cystic fibrosis transmembrane conductance regulator (CFTR) blocker glibenclamide. Inhibition of either protein kinase A (PKA) or the binding between A-kinase-anchoring proteins (AKAPs) and the regulatory PKA RII subunit blocked the 2-MeSADP-induced activation of CFTR, suggesting that PKA mediates P2Y1 receptor regulation of CFTR through one or more AKAPs. Further, the truncation of the PDZ1 domain of the scaffolding protein Na⁺/H⁺ exchanger regulatory factor-2 (NHERF-2) inhibited 2-MeSADP-dependent stimulation of Cl^– efflux, suggesting the involvement of this scaffolding protein. Activation or inhibition of PKC had no effect per se on basal Cl^– efflux but potentiated or reduced the 2-MeSADP-dependent stimulation of Cl^– efflux, respectively. These data suggest that the X. laevis P2Y1 receptor in A6 cells can increase both cAMP/PKA and Ca²⁺/PKC intracellular levels and that the PKC pathway is involved in CFTR activation via potentiation of the PKA pathway.