Figure 5.

Ability of Ruthenium Red and Capsazepine to block low pH-induced responses in rat- and human-VR1 expressing CHO cells. (a) Low pH solutions stimulate uptake of Ca²⁺ in CHO cells that express aequorin and either rat or human VR1. Rat VR1 is more sensitive to low pH with a significant stimulation seen at pH 6.0 whereas human VR1 is not activated until pH is dropped to 5.5. CHO cells that express aequorin but not receptor show no calcium signal at low pH. (b) CHO cells that express aequorin and either rat or human VR1were preincubated with a range of capsazepine concentrations and challenged with pH 5 buffer as in Figure 4a. Capsazepine completely inhibited the human VR1 proton induced calcium signal (IC₅₀=0.31±0.02 μM), but was ineffective against the rat VR1. Signal was normalized to pH5 signal with no antagonist as 100% to allow comparison between rat and human VR1 expressing cell lines. (c) CHO cells that express aequorin and human VR1were preincubated with a range of capsazepine concentrations and challenged with pH 4.0, pH 4.5 or pH 5 buffer. Capsazepine was equally effective at blocking the proton-induced response at each pH used. (d) Ruthenium red was effective at blocking pH 5-induced calcium signal in both rat and human VR1 expressing cells.