KV 1/D-type potassium channels inhibit the excitability of bronchopulmonary vagal afferent nerves.

The KV 1/D-type potassium current (ID ) is an important determinant of neuronal excitability. This study explored whether and how ID channels regulate the activation of bronchopulmonary vagal afferent nerves. The single-neuron RT-PCR assay revealed that nearly all mouse bronchopulmonary nodose neurons expressed the transcripts of α-dendrotoxin (α-DTX)-sensitive, ID channel-forming KV 1.1, KV 1.2 and/or KV 1.6 α-subunits, with the expression of KV 1.6 being most prevalent. Patch-clamp recordings showed that ID , defined as the α-DTX-sensitive K+ current, activated at voltages slightly more negative than the resting membrane potential in lung-specific nodose neurons and displayed little inactivation at subthreshold voltages. Inhibition of ID channels by α-DTX depolarized the lung-specific nodose neurons and caused an increase in input resistance, decrease in rheobase, as well as increase in action potential number and firing frequency in response to suprathreshold current steps. Application of α-DTX to the lungs via trachea in the mouse ex vivo vagally innervated trachea-lungs preparation led to action potential discharges in nearly half of bronchopulmonary nodose afferent nerve fibres, including nodose C-fibres, as detected by the two-photon microscopic Ca2+ imaging technique and extracellular electrophysiological recordings. In conclusion, ID channels act as a critical brake on the activation of bronchopulmonary vagal afferent nerves by stabilizing the membrane potential, counterbalancing the subthreshold depolarization and promoting the adaptation of action potential firings. Down-regulation of ID channels, as occurs in various inflammatory diseases, may contribute to the enhanced C-fibre activity in airway diseases that are associated with excessive coughing, dyspnoea, and reflex bronchospasm and secretions. KEY POINTS: The α-dendrotoxin (α-DTX)-sensitive D-type K+ current (ID ) is an important determinant of neuronal excitability. Nearly all bronchopulmonary nodose afferent neurons in the mouse express ID and the transcripts of α-DTX-sensitive, ID channel-forming KV 1.1, KV 1.2 and/or KV 1.6 α-subunits. Inhibition of ID channels by α-DTX depolarizes the bronchopulmonary nodose neurons, reduces the minimal depolarizing current needed to evoke an action potential (AP) and increases AP number and AP firing frequency in response to suprathreshold stimulations. Application of α-DTX to the lungs ex vivo elicits AP discharges in about half of bronchopulmonary nodose C-fibre terminals. Our novel finding that ID channels act as a critical brake on the activation of bronchopulmonary vagal afferent nerves suggests that their down-regulation, as occurs in various inflammatory diseases, may contribute to the enhanced C-fibre activity in airway inflammation associated with excessive respiratory symptoms.

Different sensitivity of action potential generation to the rate of depolarization in vagal afferent A-fiber versus C-fiber neurons.

This study demonstrates that the action potential discharge in vagal afferent A-fiber neurons is about 20 times more sensitive to the rate of membrane depolarization compared to C-fiber neurons. The sensitivity of action potential generation to the depolarization rate in vagal sensory neurons is independent of the intensity of current stimuli but nearly abrogated by inhibiting the D-type potassium channel. These findings help better understand the mechanisms that control the activation of vagal afferent nerves.

Expression of proteinase-activated receptor-2 and transient receptor potential A1 in vagal afferent nerve of rat after lung schemia-reperfusion injury.

Lung ischemia-reperfusion injury (LIRI) is a common and severe clinical complication. As the injury occurs, the pulmonary afferent nerves play an important role in regulating respiratory functions under pathophysiological conditions. The purpose of this study was to examine expression of proteinaseactivated receptor-2 (PAR2) and transient receptor potential A1 (TRPA1) in pulmonary vagal afferent nerves of LIRI and further to determine molecular mediators linking activation of PAR2 and TRPA1. A rat model of LIRI was used. Enzyme-linked immunosorbent assay (ELISA) and Western blot analysis were employed to examine pro-inflammatory cytokines (PICs, i.e., IL-1ß, IL-6 and TNF-α), and the protein levels of PIC receptors, PAR2, TRPA1, and intracellular signals. In the results, IL-1ß, IL-6 and TNF-α along with their receptors were amplified in afferent nerves of LIRI rats as compared with control rats. Sensory PAR2 and TRPA1 were also upregulated by LIRI. Blocking PAR2 by infusion of FSLLRY-NH2 attenuated upregulation of TRPA1 via intracellular signals, namely p38-MAPK and JNK. Moreover, blocking individual PIC receptor attenuated PAR2 and TRPA1 in pulmonary vagal afferent nerves. Our data showed specific signaling pathways leading LIRI to activation of PIC signal and activation of PAR2 and TRPA1 in pulmonary vagal afferent nerves via intracellular mediators. Targeting one or more of these signaling molecules may present opportunities to improve the abnormalities in vagal afferent nerve-mediated respiratory functions observed as LIRI occurs.

Secretion of a gastrointestinal hormone, cholecystokinin, by hop-derived bitter components activates sympathetic nerves in brown adipose tissue.

Matured hop bitter acids (MHBA) are oxidation products from bitter components in hops, which are used widely as food materials to add flavor and bitterness in beer production. Our previous study has shown that MHBA induces thermogenesis in brown adipose tissue (BAT) via sympathetic nerves in rodents and reduces body fat in healthy adults. However, it is unclear how MHBA affects the sympathetic nervous system. In this study, we demonstrate that MHBA treatment of enteroendocrine cells increases Ca2+ levels and induces the secretion of the gastrointestinal hormone, cholecystokinin (CCK), in a dose-dependent manner. These effects were eliminated by Ca2+ depletion from the medium or blockers of L-type voltage-sensitive Ca2+ channels during pretreatment. Induction of CCK secretion by MHBA was also confirmed using isolated rat small intestines. Elevation of the sympathetic nerve activity innervating BAT (BAT-SNA) and BAT temperature by MHBA administration in rats was blocked by pretreatment with a CCK receptor 1 (CCK1R) antagonist. Moreover, the intraperitoneal injection of CCK fragment elevated BAT-SNA, and this increase was blocked by subdiaphragmatic vagotomy. These results demonstrate that MHBA induces CCK secretion in the gastrointestinal tracts and elevates BAT-SNA via CCK1R and vagal afferent nerves. In addition, MHBA increases BAT temperature via CCK1R. Our findings reveal a novel mechanism of the beneficial metabolic effects of food ingredients.