Effect of olvanil and anandamide on vagal C-fiber subtypes in guinea pig lung

Abstract

Certain fatty acid amides such as anandamide (AEA) and olvanil are agonists for the transient receptor potential, vanilloid-1 (TRPV1) receptor, but have been found to activate TRPV1-containing C-fibers in some tissues but not others. We used extracellular recording and whole-cell patch clamp techniques to investigate the effect of olvanil and AEA on different types of vagal C-fibers innervating the same tissue, namely jugular and nodose vagal C-fibers in guinea pig lungs. A 30 s exposure to AEA and olvanil caused action potential discharge in all nodose C-fiber innervating lung but failed to activate jugular C-fibers innervating lung and airways. The activation of nodose C-fibers was blocked by the TRPV1 antagonist iodo-resiniferatoxin. In whole-cell patch clamp recordings of dissociated nodose and jugular capsaicin-sensitive neurons labeled from lungs and airways, olvanil induced large TRPV1-dependent inward currents in cell bodies of both nodose and jugular ganglion neurons. Prolonged exposure (up to 5 min) to olvanil caused action potential discharge in jugular C-fiber innervating lung but the onset latency was four times longer in jugular than in nodose C-fibers. The onsets of capsaicin response in nodose and jugular C-fibers were not different. Decreasing the tissue temperature to 25 degrees C increased the onset latency of olvanil-induced activation of nodose C-fibers 2-3-fold, but did not effect the latency of the capsaicin response. Capsaicin, olvanil, and AEA stimulate jugular C-fibers leading to tachykinergic contractions of isolated bronchi. The time to reach half-maximum is more than four times longer for olvanil and AEA, as compared to capsaicin in evoking contractions. We conclude that brief exposure to certain fatty acid amides, such as AEA and olvanil activate nodose but not jugular C-fiber terminals in the lungs. We hypothesize that this is because the nodose C-fiber terminals are equipped with a temperature-dependent mechanism for effectively and rapidly transporting the TRPV1 agonists so that they gain access to the intracellular binding sites on TRPV1. This transport mechanism may be differently expressed in two distinct subtypes of pulmonary C-fiber terminals innervating the same tissue.

Figure 1

Extracellular recordings of intrapulmonary nodose and jugular C fibers in isolated lung preparation. (a) A 30 s infusion with either anandamide (10 μM) or olvanil (Olv, 1 μM) evoked action potential discharge in a nodose capsaicin-sensitive C-fiber. Iodo-resiniferatoxin (I-RTX, 1 μM for 20 min), a selective TRPV1 antagonist, completely blocked the response evoked by 30 s infusion with olvanil in an intrapulmonary nodose C fiber. (b) By contrast, a 30 s infusion with Olvanil typically did not evoke action potential discharge in jugular C-fibers. All 17 tested nodose C fibers but only two of 12 jugular C fibers responded to olvanil. Two different subtypes of vagal C-fibers showed difference in olvanil sensitivity (P<0.001, χ²-test).

Figure 2

Whole-cell patch clamp recording of an olvanil-induced inward current in an airway-labeled jugular neuron. Olvanil (1 μM, 30 s) evoked inward currents in 12 of 13 nodose and eight of 10 jugular airway-labeled capsaicin-sensitive neurons. The histogram shows that the peak inward current induced by olvanil were similar between nodose and jugular capsaicin-sensitive neurons. The recording also shows that the olvanil-induced current in the jugular neuron was blocked by I-RTX (1 μM, 5 min). The same result was obtained in nodose neurons (n=3).

Figure 3

The latency of response to olvanil. (a) Prolonged exposure of olvanil (1 μM, >1 min) evoked action potential discharge with long latency of response in jugular C fibers (n=5). (b) The histogram shows that onset latency of the olvanil response in intrapulmonary jugular C-fibers, relative to the latency of the capsicin response, was two-fold longer than that observed for intrapulmonary C-fibers (^*P<0.05; n= 5 and 8 for jugular and nodose responses, respectively). (c) Representative olvanil response showing the delayed onset in a nodose C fiber in tissue studied at 25°C. Decreasing temperature prolonged the onset latencies of olvanil response in nodose C fibers (see text for details).

Figure 4

Representative traces of guinea pig isolated bronchial contractions to capsaicin, olvanil, and anandamide. These contractions are caused by tachykinin release (see text for details). The numbers in parentheses represent the time required to reach 50% of the maximum response (t_1/2). The t_1/2 was significantly different between capsaicin and either olvanil or anandamide (P<0.01). The values represent the mean±s.e.m. of n experiments with each experiment carried out on a tissue from different animals.