Figure 2.

Rectification and pharmacological properties of piperine-gated currents. (a) The current–voltage relationship for piperine- and capsaicin-activated currents was established using a voltage-ramp protocol (see top inset) ranging from −70 to +70 mV. A series of voltage-ramps (15 × −70 mV to +70 mV at 0.14 mV ms⁻¹) was used to capture data prior to, during and following the recovery of the agonist-induced response. The net agonist-evoked current was calculated by subtracting the mean background current from the agonist-evoked current obtained from ramps, which coincided with the steady-state phase of the response. The example shown is for a piperine-evoked response where the agonist was applied for the duration indicated by the bar. Similar experiments were conducted for capsaicin. (b) A plot of the current–voltage relationship obtained for piperine (30 μM dotted line; n=5) and capsaicin (1 μM, solid line; n=5) from pooled data generated from experiments similar to those in (a). Currents were normalised to the steady-state current observed at −70 mV and then averaged across cells. Occasional error bars (±1s.e.m.) are shown at 10 mV intervals. Piperine responses show clear outward rectification (I_+70 mV/I_−70 mV=25±4 compared to 24±5 for capsaicin; P=0.87, unpaired Student's t-test) and exhibit a reversal potential close to zero (E_rev=0.0±0.4 mV compared to −1.0±0.8 mV for capsaicin; P=0.29, unpaired Student's t-test). (c) Piperine-evoked currents (clear bar; 30 μM) were inhibited by coapplication of capsazepine 10 μM or ruthenium red 10 μM (grey bars). (d) Pooled data showing the % block of the piperine-evoked current expressed by capsazepine, (n=3) and ruthenium red, (n=4).