Figure 2

PGE₂ increases TRPV1 activity through EP₁ receptors in a PKC-dependent manner in HEK293 cells. (A) and (B) Treatment with PGE₂ (1.5 min) potentiates capsaicin-evoked responses in cells expressing rat TRPV1 with mouse EP₁ receptors, but not with other mouse EP receptors. Cells were pretreated with PGE₂ (1 μM) for 1.5 or 6.5 min before second capsaicin (20 nM) application. V_h: -60 mV. Currents were normalized as described in Figure 1. * p < 0.05 vs. control (Cont.). Numbers in parenthesis indicate cells tested. (C) Capsaicin dose-response curves for TRPV1 activation in the absence (•) and presence (○) of extracellular 1 μM PGE₂. Currents were normalized to the current maximally activated by 1 μM capsaicin in the absence of PGE₂. Figure shows averaged data fitted with the Hill equation. EC₅₀ = 81.0 nM and Hill coefficient = 1.33 in the absence of PGE₂. EC₅₀ = 27.6 nM and Hill coefficient = 1.01 in the presence of PGE₂. Data were obtained from 54 different cells. (D) Temperature threshold for TRPV1 activation was reduced in the presence of extracellular PGE₂ (1 μM). Representative temperature-response profiles in the absence (upper) and presence (lower) of PGE₂ (left). Temperature threshold for TRPV1 activation in the presence of PGE₂ (30.6 ± 1.1°C) was significantly lower than that in the absence of PGE₂ (40.7 ± 0.3°C) (right). * p < 0.05 vs. PGE₂ (-). Numbers in parenthesis indicate cells tested. (E) Proton-evoked TRPV1 responses were significantly potentiated by PGE₂ (1 μM). * p < 0.01 vs. PGE₂ (-). (F) PKC-dependent pathway is involved in the PGE₂ (1 μM, 1.5 min)-induced potentiation of capsaicin-activated currents. In some experiments, calphostin C (Calp. C) (1 μM) or PKCε translocation inhibitor (PKCε-I) (200 μM) was included in the pipette solution. Currents were normalized as described in Figure 1. Numbers in parenthesis indicate cells tested. * p < 0.05 vs. Cont. V_h: -60 mV.