POTENTIATION OF RABBIT TRIGEMINAL RESPONSES TO CAPSAICIN IN A LOW PH ENVIRONMENT

The sensitivity of 35 adult rabbit trigeminal ganglion neurons to low pH (pH 6.0), 10 mu M capsaicin (CAP) and 10 mu M capsaicin at low pH ( CAP@pH6.0) was studied using voltage-clamp whole-cell recording techni ques. Neurons responded to pH 6.0 with a transient inward current, fol lowed by a more slowly activating (sustained) net inward current. Resp onses to capsaicin showed only a sustained current. Capsaicin caused a n increase in membrane conductance, whereas responses to low pH were a ssociated with either a net increase or decrease in conductance. A sub set of neurons (n = 14) responded to CAP@pH6.0 with a sustained curren t which exceeded the sum of the peak sustained currents evoked by CAP and pH 6.0 applied singularly by approximately a factor of 4. The curr ent was associated with a substantial increase in membrane conductance . The present results indicate that, in addition to a direct conductan ce activating effect, protons have the ability to enhance the current evoked by capsaicin.