Fig 5. Contribution of the activation of G proteins to the NA-induced suppression of capsaicin currents.

(A-B) Typical current responses in the neurons dialyzed with GDPβS (200 μM, A) and in the neurons pretreated with PTX (100 μg/ml, B). Capsaicin (1 μM) was applied for 30 s three times at intervals of 15 min to the same neuron (left panels). NA (1 pM) was applied 2 min before the second capsaicin stimulation for 4.5 min (right panels). Dashed lines in panels A and B indicate zero current level. (C) The relative peak amplitudes of the capsaicin currents by the second stimulation to those by the first stimulation in each neuron are shown (2nd/1st response). The columns and vertical bars indicate the mean ± SEM (n = 5, 8, 5, 6, 5 and 5 from the left). * P < 0.05 against the control data in the absence of NA (none).