Chronic alteration in phosphatidylinositol 4,5-biphosphate levels regulates capsaicin and mustard oil responses

There is an agreement that acute (in minutes) hydrolysis and accumulation of phosphatidylinositol 4,5-bisphosphate (PIP₂) modulate TRPV1 and TRPA1 activities. Because inflammation results in PIP₂ depletion, persisting for long periods (hours to days) in pain models and in the clinic, we examined whether chronic depletion and accumulation of PIP₂ affect capsaicin (CAP) and mustard oil (MO) responses. In addition, we wanted to evaluate whether the effects of PIP₂ depend on TRPV1 and TRPA1 coexpression and whether the PIP₂ actions vary in expression cells vs. sensory neurons. Chronic PIP₂ production was stimulated by overexpression of phosphatidylinositol-4-phosphate-5-kinase, and PIP₂-specific phospholipid 5'-phosphatase was selected to reduce plasma membrane levels of PIP₂. Our results demonstrate that CAP (100 nM) responses and receptor tachyphylaxis are not significantly influenced by chronic changes in PIP₂ levels in wild-type (WT) or TRPA1 null-mutant sensory neurons as well as CHO cells expressing TRPV1 alone or with TRPA1. However, low concentrations of CAP (20 nM) produced a higher response after PIP₂ depletion in cells containing TRPV1 alone but not TRPV1 together with TRPA1. MO (25 μM) responses were also not affected by PIP₂ in WT sensory neurons and cells coexpressing TRPA1 and TRPV1. In contrast, PIP₂ reduction leads to pronounced tachyphylaxis to MO in cells with both channels. Chronic effect of PIP₂ on TRPA1 activity depends on presence of the TRPV1 channel and cell type (CHO vs. sensory neurons). In summary, chronic alterations in PIP₂ levels regulate magnitude of CAP and MO responses as well as MO tachyphylaxis. This regulation depends on coexpression profile of TRPA1 and TRPV1 and cell type.