Figure 7. Synergistic effects of capsaicin and osmotic stimuli on TRPV1.

(A) Representative single cell traces of the fluorescence ratio upon application of 1.5 nM capsaicin solutions (arrowhead) under various conditions of osmolality in HEK293-TRPV1 cells. The top black line indicates that the extracellular fluid with indicated osmolalities was applied before the capsaicin addition. Responses to capsaicin changed markedly with osmolality. (B) Summary of the change in the fluorescence ratio. Response of TRPV1 to hyperosmolality was markedly potentiated in the presence of capsaicin (compare filled circles with filled triangles). No response was observed in HEK293 cells (open circles). Data obtained at the peak was used to obtain the mean of the response. (C) Summary of the change in the fluorescence ratio during the perfusion of a hypertonic solution (350 mOsm) in the presence of capsaicin and indicated reagents at 36°C in HEK293-TRPV1 (filled bars) and HEK293 (open bar) cells. Cells were preincubated for 15 min with an imaging buffer (300 mOsm) containing 20 µM ruthenium red (RuR) or Ca²⁺-free solution (Ca-free). Data are differences between fluorescence ratios 2 min before and 4 min after the change of the solution. Values are the mean ± SEM; when the SEM value was less than 0.30, the error bar is hidden behind the symbol. HEK293-TRPV1: n = 305 (250 mOsm), n = 390 (300 mOsm), n = 220 (350 mOsm), n = 136 (RuR), n = 112 (Ca-free). HEK293: n = 108 (250 mOsm), n = 113 (300 mOsm), n = 114 (350 mOsm).