Phosphorylation of TRPV1 explains only small portion of heterogeneous Capsaicin Responses in Dorsal Root Ganglia Neurons

TRPV1 is at the center of pain research. Using heterologous expression systems, a number of mechanisms have been described to modulate its ion channel properties such as phosphorylation by PKC and PKA. In contrast, in large sets of dorsal root ganglia (DRG) neurons the distribution of sensitization states and to what extend kinase mediated sensitization mechanisms contribute to this have so far not been analyzed. Using high content microscopy approaches in combination with computational modeling we found a strong correlation between TRPV1-expression levels and the cellular calcium response after capsaicin exposure in transfected F-11 cells. In contrast, testing primary neurons we found no correlation but very heterogeneous responses. We hypothesized differential sensitization states such as kinase mediated phosphorylation of TRPV1 to underlie the observed heterogeneity. Therefore, pharmacologically we activated PKC and PKA, respectively, or inhibited kinases. Corroborating our hypothesis, the correlation between TRPV1 expression and capsaicin-induced Calcium-entry increased and decreased accordingly. Surprisingly, the degree of alteration of the level of correlation was rather slow. This indicates, that while in principle possible, kinase mediated sensitization plays only a minor role in establishing the observed high heterogeneity of TRPV1-calcium responses in primary sensory neurons.