Fig. 2. Nucleotides stimulate cell proliferation through P2Y₁R. P2Y₁R agonists, 2-MeSADP (A) and ADP (B), increase cell proliferation in a concentration-dependent manner (n=4-8). [³H]thymidine incorporation assays show that HeLa and FRT cells pretreated for 1 hour with different concentrations of the agonists increase their proliferation rate. The EC₅₀ of the agonists is indicated. (C) [³H]thymidine incorporation after 1 hour of stimulation with 1 µM P2YR agonist. Compared with P2Y₁R agonists 2-MeSADP, ATP and ADP, which increase cell proliferation, the P2Y₂R agonist UTP shows no effect. The P2Y₆R agonist UDP induces cell proliferation only in FRT cells. Results are normalized against control cells. Values are the means ± s.e.m. ^*P<0.05, ^**P<0.01, Dunnett's test compared with controls (n=5). (D) Cell proliferation induced by 1 µM 2-MeSADP is selectively mediated by P2Y₁R, since it was abrogated by the selective P2Y₁R antagonist MRS2179, which in turn does not affect the proliferative response to 10 µM UDP, as shown for FRT cells (n=3-4). Only the carrier culture medium was added for controls.