Background
The activation of various P2 receptors (P2R) by extracellular nucleotides promotes diverse cellular events, including the stimulation of cell signaling protein and increases in [Ca(2+)](i). We report that some agents that can block P2X(7)R receptors also promote diverse P2X(7)R-independent effects on cell signaling.
Conclusions
Several agents used as P2X(7)R blockers promote the activation of various signaling proteins and thereby act more like receptor agonists than antagonists. General significance: Some compounds used to block P2 receptors have complicated effects that may confound their use in blocking receptor activation and other biological processes for which they are employed, including their use as blockers of various ion transport proteins.
Methods
We exposed native rat parotid acinar cells, salivary gland cell lines (Par-C10, HSY, HSG), and PC12 cells to suramin, DIDS (4,4'-diisothiocyano stilbene-2,2'-disulfonic acid), Cibacron Blue 3GA, Brilliant Blue G, and the P2X(7)R-selective antagonist A438079, and examined the activation/phosphorylation of ERK1/2, PKCδ, Src, CDCP1, and other signaling proteins.
Results
With the exception of suramin, these agents blocked the phosphorylation of ERK1/2 by BzATP in rat parotid acinar cells; but higher concentrations of suramin blocked ATP-stimulated (45)Ca(2+) entry. Aside from A438079, these agents increased the phosphorylation of ERK1/2, Src, PKCδ, and other proteins (including Dok-1) within minutes in an agent- and cell type-specific manner in the absence of a P2X(7)R ligand. The stimulatory effect of these compounds on the tyrosine phosphorylation of CDCP1 and its Src-dependent association with PKCδ was blocked by knockdown of CDCP1, which also blocked Src and PKCδ phosphorylation. Conclusions: Several agents used as P2X(7)R blockers promote the activation of various signaling proteins and thereby act more like receptor agonists than antagonists. General significance: Some compounds used to block P2 receptors have complicated effects that may confound their use in blocking receptor activation and other biological processes for which they are employed, including their use as blockers of various ion transport proteins.
Significance
Some compounds used to block P2 receptors have complicated effects that may confound their use in blocking receptor activation and other biological processes for which they are employed, including their use as blockers of various ion transport proteins.