Background: Cell surface receptors for adenosine 5'-triphosphate (ATP; P2 receptors) have been subdivided into two families: ligand-gated ion channels (P2X1-7) and G-protein-coupled (P2Y1-8) receptors. We investigated the potential role of P2 receptors on rat glomerular mesangial cells.
Methods: To investigate cell proliferation, DNA synthesis was assayed by measuring [3H]thymidine incorporation into DNA. For detecting apoptosis, morphological features, DNA fragmentation, and exposure of phosphatidylserine on the outside surface of the cell membrane were investigated. Expression of mRNA and distribution of receptors were detected by reverse transcription-polymerase chain reaction and immunohistochemistry, respectively.
Results: ATP triggered a dose-dependent increase in DNA synthesis. This response was also induced by uridine triphosphate (UTP), an agonist equipotent with ATP at P2Y2 and P2Y4 receptors; both P2Y2 and P2Y4 mRNA are expressed in glomerular mesangial cells and isolated glomeruli. In contrast, the P2X7 receptor agonist 2'-83'-O-(4-benzoyl benzoyl) ATP (BzATP) caused a decrease in cell number. BzATP produced DNA cleavage and exposure of phosphatidylserine on the outside of the cell membrane. P2X7 receptors were distributed heterogeneously in unstimulated cells. The expression of P2X7 mRNA was maintained at a low level, but was induced by tumor necrosis factor-alpha.
Conclusions: Stimulation of glomerular mesangial cells via P2Y2 and/or P2Y4 and via P2X7 receptors can induce proliferation and apoptotic cell death, respectively. The balance between proliferation and apoptosis will depend on the relative stimulation and expression of these P2 receptor subtypes, and could play an important role in normal and abnormal glomerular function.