TRPV1 is known to be important in the sensitisation of sensory neurones in inflammation and nerve injury. VEGF has two counteracting splice isoform families, VEGFxxxa and VEGFxxxb (1). VEGF is involved in nociception, possibly via TRPV1, as VEGF165a causes mechanical allodynia, which is not seen in TRPV1 KO mice and is blocked by TRPV1 antagonism (Hulse et al unpublished). VEGF165a activates PKC through VEGFR2 ligand dependent activation (2), and TRPV1 is sensitised by PKC-dependent phosphorylation (3). We therefore investigated whether VEGF isoforms might modulate sensory neuronal activity by controlling TRPV1 phosphorylation by PKC. Rats were killed by anaesthetic overdose, and primary cultured DRG neurons were treated either with vehicle (HBSS) or 2.5nM VEGF165b. Varying concentrations of capsaicin (0, 0.01, 0.05, 0.1, 0.5, 1, 5, 10uM) were used to stimulate TRPV1. The resulting calcium influx response was measured on a plate reader using Fluo-4 dye as a Ca2+ indicator, and the response quantified by measuring the area under the curve relative to before capsaicin. The cultures were also incubated with or without the PKC inhibitor bisindolylmaleiemide-1 (BIM1, 10µM). In this instance sub-threshold 0.2uM capsaicin was used and the calcium response measured as above. Immortalised embryonic DRG neurons (50B11) were also cultured and treated with either vehicle, VEGF165a, VEGF165b or NGF. Protein was extracted and immunoprecipitation used to isolate TRPV1. Once isolated phosphorylated TRPV1 levels were examined by western blotting with a phosphoserine-specific antibody (n=3). VEGF165b appeared to reduce sensitisation of TRPV1. A significant suppression of TRPV1 response was seen at 0.1-5µM capsaicin in the presence of VEGF165b (p<0.001, 1-way ANOVA). BIM1 blocked the sensitisation of TRPV1 by VEGF165a, indicating a PKC-dependent mechanism. 0.2µM capsaicin with 2.5nM VEGF165a caused an increase in calcium response, which was prevented with BIM1 (p<0.01, 1-way ANOVA). VEGF165a and NGF showed an increase in phosphorylated TRPV1 by Western blotting, which VEGF165b did not. VEGF165a therefore appears to sensitise TRPV1 by PKC-dependent phosphorylation, while VEGF165b acts to suppress this sensitisation. The finding that VEGF165b did not increase phosphorylated TRPV1 levels also supports the idea that it may be involved in preventing sensitisation of TRPV1. Thus TRPV1 activation by VEGF isoforms in DRG neurons is isoform and PKC dependent.