The human P2Y11 (hP2Y11) receptor was stably expressed in two cell lines, 1321N1 human astrocytoma cells (1321N1-hP2Y11) and Chinese hamster ovary cells (CHO-hP2Y11), and its coupling to phospholipase C and adenylyl cyclase was assessed.
In 1321N1-hP2Y11 cells, ATP promoted inositol phosphate (IP) accumulation with low μM potency (EC50=8.5±0.1 μM), whereas it was 15 fold less potent (130±10 μM) in evoking cyclic AMP production.
In CHO-hP2Y11 cells, ATP promoted IP accumulation with slightly higher potency (EC50=3.6±1.3 μM) than in 1321N1-hP2Y11 cells, but it was still 15 fold less potent in promoting cyclic AMP accumulation (EC50=62.4±15.6 μM) than for IP accumulation. Comparable differences in potencies for promoting the two second messenger responses were observed with other adenosine nucleotide analogues.
In 1321N1-hP2Y11 and CHO-hP2Y11 cells, down regulation of PKC by chronic treatment with phorbol ester decreased ATP-promoted cyclic AMP accumulation by 60 – 80% (P<0.001) with no change in its potency. Likewise, chelation of intracellular Ca2+ decreased ATP-promoted cyclic AMP accumulation by ∼45% in 1321N1-hP2Y11 cells, whereas chelation had no effect on either the efficacy or potency of ATP in CHO-hP2Y11 cells.
We conclude that coupling of hP2Y11 receptors to adenylyl cyclase in these cell lines is much weaker than coupling to phospholipase C, and that activation of PKC and intracellular Ca2+ mobilization as consequences of inositol lipid hydrolysis potentiates the capacity of ATP to increase cyclic AMP accumulation in both 1321N1-hP2Y11 and CHO-hP2Y11 cells.
British Journal of Pharmacology (2001) 132, 318–326; doi:10.1038/sj.bjp.0703788