Article Figures & Data
Figures
- Fig. 1.
PGE2 and forskolin treatment enhance the amplitude of the whole-cell current elicited by capsaicin.A, Voltage-clamp recording (holding potential −60 mV) obtained from a representative neuron in which PGE2treatment increased the amplitude of the current elicited by a 2 sec focal application of capsaicin. B, Sensitizing effects of 100 nm and 1 μm forskolin treatment (top and bottom traces, respectively) on capsaicin responses in two other neurons. The times indicate when these recordings were obtained after the onset of prostaglandin or forskolin treatment. The extent and time courses of sensitization induced by different concentrations of forskolin are summarized inC. The amplitude of the capsaicin response after forskolin treatment was normalized to the average of the two control responses and represented as the fold increase relative to the control value. The bar beginning at 3 min represents the change to forskolin-containing Ringer’s solution. D, Effects of dideoxyforskolin on the capsaicin response. Thehatched and open bars indicate the applications of dideoxyforskolin and PGE2, respectively. Asterisks indicate significant differences at p < 0.05 compared with control.
- Fig. 2.
Treatment with membrane-permeant analogs of cAMP enhance the whole-cell responses to capsaicin. A, Sensitizing effect of 10 μm and 1 mm8-Br-cAMP treatment (top and bottom traces, respectively) on capsaicin responses in two different neurons. B, Extent and time course of the sensitization produced by these concentrations of 8-Br-cAMP. C, Sensitization induced by 10 and 100 μmchlorphenylthio-cAMP. In B and C, thebar beginning at 3 min represents the change to Ringer’s solution containing the indicated concentrations of cAMP analogs. Asterisks indicate significant differences atp < 0.05 compared with control.
- Fig. 3.
Treatment with 8-Br-cAMP reverses the forskolin-induced sensitization. The consecutive application of 1 and 10 μm forskolin is indicated by thehatched and solid bars, respectively. In the presence of 10 μm forskolin, the addition of 1 mm 8-Br-cAMP (open bar) rapidly reversed the forskolin-induced sensitization. The inset tracesillustrate the capsaicin responses from a representative neuron at the indicated times. Asterisks indicate significant differences at p < 0.05 compared with control.
- Fig. 4.
PKI14–24 treatment blocks both the PGE2- and forskolin-induced sensitization.A, Results from experiments with PKI14–24and PGE2 treatment. The hatched andopen bars indicate the addition of PKI14–24and PGE2, respectively. B, Results from experiments with PKI14–24 and forskolin treatments. The hatched and open bars indicate the presence of PKI14–24 and forskolin, respectively. Theinset traces illustrate representative responses to capsaicin from two different neurons for each experimental condition at the times indicated. Asterisks indicate significant differences atp < 0.05 compared with control.
- Fig. 5.
Capsaicin elicits single-channel activity that is blocked by capsazepine. A, Representative recording from a cell-attached patch held at −60 mV. Changing the superfusate from the low-calcium external solution (trace 1) to one containing 1 μm capsaicin (CAP) promoted single-channel activity that was blocked reversibly by 10 μm capsazepine (CAP + CZP).B, Selected portions of the compressed traces shown inA at greater time resolution. The numbered traces in B represent the channel activity observed for those specific portions indicated by their respective numbers under the traces of A. The arrowsindicate the closed level for each trace. C, All-points histogram generated from a 40 sec recording during the first application of capsaicin to this neuron. D, Effect of capsaicin and capsaicin-capsazepine treatment on the mean NPo in three cell-attached patches.Asterisks indicate significant differences atp < 0.05 compared with control.
- Fig. 6.
NPo depends on the concentration of capsaicin. These results summarize the effect of increasing concentrations of bath-applied capsaicin on mean NPo in eight cell-attached patches. The line through the data points represents the fit obtained for the ligand-binding isotherm as described in Materials and Methods.
- Fig. 7.
The capsaicin-gated channel exhibits outward rectification and increased NPo at positive membrane potentials. A, Effect of membrane potential on the single-channel activity elicited by bath exposure to 1 μmcapsaicin in a representative patch. The arrows indicate the closed level for each trace. The membrane potential for each trace is provided at the right. B, Current–voltage relation obtained from recordings in which the number of sensory neurons ranged between three and nine. Theinset shows a representative current-clamp recording for the depolarization (to −3 mV) elicited by treatment with 1 μm capsaicin. C, Dependence of the relative NPo elicited by 1 μm capsaicin (normalized to that obtained at +60 mV) on membrane potential (n = 3). The line through thebars represents the fit described by the Boltzmann relation.
- Fig. 8.
PGE2 treatment enhances the channel activity elicited by capsaicin. A, Representative recording of the single-channel activity elicited by 300 nmcapsaicin under control conditions. In B, the single-channel activity elicited by capsaicin is increased after treatment with 1 μm PGE2 in the same neuron. The inset trace shows, at greater time resolution, the capsaicin response during the period indicated by thebar. The transient nature of the PGE2-induced increase in channel activity is shown inC. The trace illustrates the recording obtained after 20 min of continuous exposure to PGE2.D, Effect of 10 μm capsaicin treatment in this same neuron after a 25 min exposure to PGE2. Theinset illustrates the response to capsaicin obtained during the time indicated by the bar. In all traces, thearrows indicate the closed level. The all-points histogram generated for each trace is provided at theright.
- Fig. 9.
PGE2 or forskolin treatment transiently increases NPo of the capsaicin-gated channel. The hatched bar indicates the time and duration for the application of each agent. Asterisks indicate significant differences at p < 0.05 compared with control.
