Purinergic inhibition of Na-K-Cl cotransport has been noted in various renal epithelial cells derived from the collecting tubule, including Madin-Darby canine kidney (MDCK) cells. In recent studies, we have observed purinergic inhibition of Na-K-Cl cotransport in C11-MDCK subclones (alpha-intercalated-like cells). Interestingly, Na-K-Cl cotransport activity was also detected in C7-MDCK subclones (principal-like cells) but was not affected by ATP. In this investigation, we have transfected the human Na-K-Cl cotransporter (huNKCC1) in both C11 and C7 cells to determine whether these differences in NKCC regulation by ATP were due to cell-specific purinoceptor signaling pathways or to cell-specific isoforms/splice variants of the transporter. In both cell lines, we found that endogenous as well as huNKCC1-derived cotransport activity was restricted to the basolateral side. In addition, we were able to show that extracellular application of 100 microM ATP or 100 microM UTP abolished NKCC activity in both mock- and huNKCC1-transfected C11 cells but not in mock- and huNKCC1-transfected C7 cells; in C11 cells, intriguingly, this inhibition was not affected by inhibitors of RNA and protein synthesis and occurred even though expression levels of UTP-sensitive P2Y2-, P2Y4-, and P2Y6-purinoceptors were not different from those observed in C7 cells. These results suggest that C11 cells express an undetermined type of UTP-sensitive P2-purinoceptors or a unique P2Y-purinoceptor-triggered signaling cascade that leads to inhibition of NKCC1.

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