Bradykinin activates airway parasympathetic ganglion neurons by inhibiting M-currents

The KCNQ channel inhibitor XE991 suppresses nicotinic acetylcholine receptor-mediated responses in rat intracardiac ganglion neurons

BACKGROUND

XE991 (10,10-bis(4-pyridinylmethyl)-9(10H)-anthracenone) is reportedly a potent and selective Kv7 (KCNQ) channel inhibitor. This study aimed to evaluate how XE991 affects nicotinic responses in intracardiac ganglion neurons.

METHODS

We studied how the KCNQ channel inhibitor XE991 could affect nicotinic responses in acutely isolated rat intracardiac ganglion neurons using a perforated patch-clamp recording configuration and Ca²⁺ imaging.

RESULTS

XE991 reversibly and concentration-dependently inhibited the nicotine (10 μM)-induced current with an IC₅₀ of 14.4 μM. The EC₅₀ values for nicotine-induced currents in the absence and presence of 10 μM XE991 were 8.7 and 12.0 μM, respectively. Because XE991 suppressed the maximum response of the nicotine concentration-response curve, the inhibitory effect of this drug appears to be noncompetitive. In addition, linopirdine reduced the amplitude of 10 µM nicotine-induced currents with an IC₅₀ value of 16.9 μM. The inorganic KCNQ channel inhibitor Ba²⁺ affected neither the nicotine-induced current nor the inhibitory effect of XE991 on the nicotinic response. The KCNQ activator flupirtine at a concentration of 10 μM slightly but markedly inhibited the nicotine-induced current. Finally, XE991 inhibited the nicotine-induced elevation of intracellular calcium concentration and the nicotine-induced firing of action potentials.

CONCLUSION

We propose that XE991 inhibits nicotinic acetylcholine receptors in intracardiac ganglion neurons, which in turn attenuate nicotine-induced neuronal excitation.

Excitatory effect of bradykinin on intrinsic neurons of the rat heart

The heart receives sympathetic and parasympathetic innervation through the intrinsic cardiac nervous system. Although bradykinin (BK) has negative inotropic and chronotropic properties of cardiac contraction, the direct effect of BK on the intrinsic neural network of the heart is still unclear. In the present study, the effect of BK on the intracardiac ganglion neurons isolated from rats was investigated using the perforated patch-clamp technique. Under current-clamp conditions, application of 0.1 μM BK depolarized the membrane, accompanied by repetitive firing of action potentials. When BK was applied repeatedly, the second responses were considerably less intense than the first application. The BK action was fully inhibited by the B₂ receptor antagonist Hoe-140, but not by the B₁ receptor antagonist des-Arg⁹-[Leu⁸]-BK. The BK response was mimicked by the B₂ agonist [Hyp³]-BK. The BK-induced depolarization was inhibited by the phospholipase C inhibitor U-73122. BK evoked inward currents under voltage-clamp conditions at a holding potential of -60 mV. Removal of extracellular Ca²⁺ markedly increased the BK-induced currents, suggesting an involvement of Ca²⁺-permeable non-selective cation channels. The muscarinic agonist oxotremorine-M (OxoM) also elicited the extracellular Ca²⁺-sensitive cationic currents. The OxoM response did not exhibit rundown with repeated agonist application. The amplitude of current evoked by 1 μM OxoM was comparable to that induced by 0.1 μM BK. Co-application of 0.1 μM BK and 1 μM OxoM elicited the current whose peak amplitude was almost the same as that elicited by OxoM alone, suggesting that BK and OxoM activate same cation channels. BK also reduced the amplitude of M-current, while the M-current inhibitor XE-991 affected neither resting membrane potential nor the BK-induced depolarization. From these results, we suggest that BK regulates excitability of intrinsic cardiac neurons by both an activation of non-selective cation channels and an inhibition of M-type K⁺ channels through B₂ receptors.

Modulation of cardiac vagal tone by bradykinin acting on nucleus ambiguus

Bradykinin (BK), a component of the kallikrein-kininogen-kinin system exerts multiple effects via B1 and B2 receptor activation. In the cardiovascular system, bradykinin has cardioprotective and vasodilator properties. We investigated the effect of BK on cardiac-projecting neurons of nucleus ambiguus, a key site for the parasympathetic cardiac regulation. BK produced a dose-dependent increase in cytosolic Ca²⁺ concentration. Pretreatment with HOE140, a B2 receptor antagonist, but not with R715, a B1 receptor antagonist, abolished the response to BK. A selective B2 receptor agonist, but not a B1 receptor agonist, elicited an increase in cytosolic Ca²⁺ similarly to BK. Inhibition of N-type voltage-gated Ca²⁺ channels with ω-conotoxin GVIA had no effect on the Ca²⁺ signal produced by BK, while pretreatment with ω-conotoxin MVIIC, a blocker of P/Q-type of Ca²⁺ channels, significantly diminished the effect of BK. Pretreatment with xestospongin C and 2-aminoethoxydiphenyl borate, antagonists of inositol 1,4,5-trisphosphate receptors, abolished the response to BK. Inhibition of ryanodine receptors reduced the BK-induced Ca²⁺ increase, while disruption of lysosomal Ca²⁺ stores with bafilomycin A1 did not affect the response. BK produced a dose-dependent depolarization of nucleus ambiguus neurons, which was prevented by the B2 receptor antagonist. In vivo studies indicate that microinjection of BK into nucleus ambiguus elicited bradycardia in conscious rats via B2 receptors. In summary, in cardiac vagal neurons of nucleus ambiguus, BK activates B2 receptors promoting Ca²⁺ influx and Ca²⁺ release from endoplasmic reticulum, and membrane depolarization; these effects are translated in vivo by bradycardia.

The effects of suplatast tosilate on acutely dissociated sensory and paratracheal ganglia neurons

In this study, we investigated the effects of suplatast on acutely dissociated single neurons of sensory and paratracheal ganglia using a patch-clamp technique. Suplatast had little effect on various responses caused by capsaicin, acid, bradykinin, serotonin and adenosine 5'-triphosphate in rat sensory neurons. Suplatast, even at 10-3 M, also did not induce any current at various membrane potentials in rat and guinea pig paratracheal ganglia neurons. Further, acetylcholine- and bradykinin-induced depolarizations were not affected by suplatast. On the other hand, in rat paratracheal ganglia neurons, 10-5 M nicotine-induced current were inhibited by suplatast in a concentration-dependent manner with a 50% inhibitory concentration of 9.86x10-5 M. The effect was noncompetitive and voltage-dependent. Furthermore, the effect was use-independent and not affected by the pretreatment time of suplatast. The results suggested that suplatast may inhibit neurotransmission at the paratracheal ganglia via the inhibition of nicotinic current. Thus, suplatast may attenuate cough production through the improvement of pathological conditions of the lower airway via suppressed acetylcholine release from the postganglionic nerve terminal.

Cholinergic EPSCs and their potentiation by bradykinin in single paratracheal ganglion neurons attached with presynaptic boutons

We have found that bradykinin (BK) potentiates the nicotine-induced currents in airway paratracheal/parabronchial ganglia (PTG) neurons. In this study, we investigated if BK affects the cholinergic synaptic transmission in rat PTG neurons attached with synaptic buttons. Excitatory postsynaptic currents (EPSCs) were recorded in acutely dissociated PTG neurons attached with presynaptic boutons. EPSC frequency was increased in the high-K(+) external solution without affecting their amplitude. Activation and deactivation kinetics also did not change in the high-K(+) solution. Cd(2+) inhibited the EPSC frequency at 10(-7) M and also amplitude at higher concentrations without changing the kinetics. Mecamylamine inhibited both the amplitude and frequency of EPSCs and reduced the activation and deactivation kinetics. 10(-8) M BK potentiated the EPSC amplitude to 1.37 ± 0.19 times of preapplication control. In addition, its frequency was increased to 2.04 ± 0.41 times. BK did not affect the activation and deactivation kinetics. The effects of BK were mimicked by [Hyp(3)]-BK, a B2 kinin receptor agonist, whereas HOE 140, a B2 kinin receptor antagonist, abolished the effects of BK. In conclusion, BK potentiates the cholinergic synaptic transmission via B2 kinin receptors in the PTG. Since predominant control of airway function is thought to be exerted by cholinergic nerves arising from the PTG, the present findings might underlie at least partly the inflammatory pathological conditions of the lower airway.

Central and peripheral mechanisms of narcotic antitussives: codeine-sensitive and -resistant coughs

Narcotic antitussives such as codeine reveal the antitussive effect primarily via the mu-opioid receptor in the central nervous system (CNS). The kappa-opioid receptor also seems to contribute partly to the production of the antitussive effect of the drugs. There is controversy as to whether delta-receptors are involved in promoting an antitussive effect. Peripheral opioid receptors seem to have certain limited roles. Although narcotic antitussives are the most potent antitussives at present, certain types of coughs, such as chronic cough, are particularly difficult to suppress even with codeine. In guinea pigs, coughs elicited by mechanical stimulation of the bifurcation of the trachea were not able to be suppressed by codeine. In gupigs with sub-acute bronchitis caused by SO2 gas exposure, coughing is difficult to inhibit with centrally acting antitussives such as codeine. Some studies suggest that neurokinins are involved in the development of codeine-resistant coughs. However, evidence supporting this claim is still insufficient. It is very important to characterize opiate-resistant coughs in experimental animals, and to determine which experimentally induced coughs correspond to which types of cough in humans. In this review, we describe the mechanisms of antitussive effects of narcotic antitussives, addressing codeine-sensitive and -resistant coughs, and including our own results.

Inhibition of the serotonin-induced inward current by dextromethorphan in rat nodose ganglion neurons

Dextromethorphan is one of the most widely used antitussives for the treatment of cough. In the present study, we investigated the effect of dextromethorphan on 5-hydroxytryptamine (5-HT)-induced currents in acutely dissociated rat nodose ganglion neurons using nystatin-perforated patch-clamp recording configuration. The 5-HT-induced current was inhibited by the 5-HT(3) receptor antagonist tropisetron, while the selective 5-HT(3) receptor agonist 1-(m-chlorophenyl)-biguanide hydrochloride (mCPBG) induced a similar current. Dextromethorphan reversibly and concentration-dependently inhibited the 5-HT-induced inward current. The inhibition did not appear to be voltage-dependent. Both the peak and steady-state 5-HT-induced currents were inhibited by dextromethorphan, although the peak current was more sensitive to dextromethorphan block. The IC(50) values for the inhibition of peak and steady currents evoked by 3 muM 5-HT were 16.4 and 34.4 muM, respectively. In the presence of 10 muM dextromethorphan, the concentration-response curve for 5-HT was shifted to the right without changing the maximum response, while high concentrations reduced the maximum current. The 5-HT EC(50) values in the presence of 0, 10, 30 and 60 muM dextromethorphan were 4.3, 6.8, 15.5 and 40.6 muM, respectively. The results indicate that dextromethorphan inhibits the 5-HT-induced current of rat nodose ganglion neurons, and further suggest that dextromethorphan at a low concentration acts as a competitive inhibitor of 5-HT(3) receptors.

Potentiation of nicotinic currents by bradykinin in the paratracheal ganglia neurons of rats

The effects of bradykinin on nicotine-induced responses were investigated in neurons dissociated from rat paratracheal ganglia using the nystatin-perforated patch-clamp recording technique. When bradykinin (10(-9) to 10(-8) M) was pretreated and then simultaneously applied with 10(-5) M nicotine, bradykinin potentiated the nicotine-induced currents. The potentiation was mimicked by [Hyp3]-bradykinin and inhibited by HOE-140, pertussis toxin, neomycin and U-73122, but not U-73433. These results suggest that bradykinin potentiates nicotinic currents via bradykinin B2 receptor, pertussis toxin-sensitive G-protein and phospholipase C. Since bradykinin inhibits the M-current via bradykinin B2 receptor and pertussis toxin-insensitive G-protein [Mochidome, T., Ishibashi, H., Takahama, K., 2001. Bradykinin activates airway parasympathetic ganglion neurons by inhibiting M-currents. Neuroscience 105, 785-791.], it seemed that bradykinin B2 receptor activated two distinct signal transduction pathways in the paratracheal ganglia neurons. This effect of bradykinin might cause enhanced synaptic transmission in paratracheal ganglia neurons and contribute to the aggravation of pathological conditions of the lower airway via enhanced acetylcholine release from the postganglionic nerve terminals.

Noradrenaline-induced cation currents in isolated rat paratracheal ganglion neurons

The actions of noradrenaline (NA) on the neurons acutely isolated from paratracheal ganglia of rats and the ionic mechanisms involved were studied with nystatin-perforated patch recording configuration. Under current-clamp conditions, application of 10 microM NA produced membrane depolarization followed by repetitive action potentials. NA evoked an inward cationic current under voltage-clamp conditions at a holding potential of -60 mV. Transient tail inward ('hump') current was also induced by washout of NA. The NA-induced current was reduced by extracellular Ca(2+) and Mg(2+), with half-maximal concentrations of 0.7 and 2.6 mM for Ca(2+) and Mg(2+), respectively. Phenylephrine, an alpha(1)-adrenoceptor agonist, mimicked the NA-induced current, but the 'hump' current did not occur upon washout of phenylephrine. The NA-induced current was inhibited by prazosin and WB-4101, alpha(1)-adrenoceptor antagonists. In contrast, in the presence of yohimbine, an alpha(2)-adrenoceptor antagonist, the NA-induced current was potentiated and the washout of NA failed to evoke the 'hump' current. The pretreatment of paratracheal neurons with pertussis toxin also potentiated the NA-induced current. The NA-induced inward current was inhibited by pretreatment with U73122, a phospholipase C inhibitor, and xestospongin-C, a membrane-permeable IP(3) receptor antagonist. On the other hand, thapsigargin, BAPTA-AM and calmidazolium had no effect on the NA-induced current, suggesting that release of Ca(2+) from intracellular Ca(2+) stores via IP(3) receptors is not involved in the NA action. The cationic channels activated by NA play an important physiological role in neuronal membrane depolarization in rat paratracheal ganglia.

[The dissociation of paratracheal ganglion neurons and its application to neuropharmacology]

It is generally considered that dominant excitatory control of the airway is exerted by the parasympathetic nervous system. In the lower airway, there are a number of parasympathetic ganglia on the serosal surface of the dorsal tracheal wall. The dissociation of these paratracheal ganglion neurons facilitates the ability to visualize and patch-clamp single-neurons and to control the surrounding solutions. This article describes technical procedures to obtain the single paratracheal neurons and its application to neuropharmacology. The single paratracheal neurons can be isolated with adherent functional synaptic terminals using a weak enzyme treatment. This will allow investigations of the mechanisms and modulation of neurotransmitter release from vagal preganglionic nerve terminals with unprecedented ease and accuracy.

Sympathoexcitation by bradykinin involves Ca2+-independent protein kinase C

Bradykinin has long been known to excite sympathetic neurons via B(2) receptors, and this action is believed to be mediated by an inhibition of M-currents via phospholipase C and inositol trisphosphate-dependent increases in intracellular Ca(2+). In primary cultures of rat superior cervical ganglion neurons, bradykinin caused an accumulation of inositol trisphosphate, an inhibition of M-currents, and a stimulation of action potential-mediated transmitter release. Blockade of inositol trisphosphate-dependent signaling cascades failed to affect the bradykinin-induced release of noradrenaline, but prevented the peptide-induced inhibition of M-currents. In contrast, inhibition or downregulation of protein kinase C reduced the stimulation of transmitter release, but not the inhibition of M-currents, by bradykinin. In cultures of superior cervical ganglia, classical (alpha, betaI, betaII), novel (delta, epsilon), and atypical (zeta) protein kinase C isozymes were detected by immunoblotting. Bradykinin induced a translocation of Ca(2+)-independent protein kinase C isoforms (delta and epsilon) from the cytosol to the membrane of the neurons, but left the cellular distribution of other isoforms unchanged. This activation of Ca(2+)-independent protein kinase C enzymes was prevented by a phospholipase C inhibitor. The bradykinin-dependent stimulation of noradrenaline release was reduced by inhibitors of classical and novel protein kinase C isozymes, but not by an inhibitor selective for Ca(2+)-dependent isoforms. These results demonstrate that bradykinin B(2) receptors are linked to phospholipase C to simultaneously activate two signaling pathways: one mediates an inositol trisphosphate- and Ca(2+)-dependent inhibition of M-currents, the other one leads to an excitation of sympathetic neurons independently of changes in M-currents through an activation of Ca(2+)-insensitive protein kinase C.