Acetylcholine-activated ionic currents in isolated paratracheal ganglion cells of the rat

Autonomic neural control of intrathoracic airways

Autonomic neural control of the intrathoracic airways aids in optimizing air flow and gas exchange. In addition, and perhaps more importantly, the autonomic nervous system contributes to host defense of the respiratory tract. These functions are accomplished by tightly regulating airway caliber, blood flow, and secretions. Although both the sympathetic and parasympathetic branches of the autonomic nervous system innervate the airways, it is the later that dominates, especially with respect to control of airway smooth muscle and secretions. Parasympathetic tone in the airways is regulated by reflex activity often initiated by activation of airway stretch receptors and polymodal nociceptors. This review discusses the preganglionic, ganglionic, and postganglionic mechanisms of airway autonomic innervation. Additionally, it provides a brief overview of how dysregulation of the airway autonomic nervous system may contribute to respiratory diseases.

Neuro-endocrine-immune network and inflammatory bowel disease

Inflammatory bowel disease (IBD) is a group of chronic inflammatory gastrointestinal diseases of unknown etiology, including mainly ulcerative colitis (UC) and Crohn's disease (CD). Numerous studies have indicated that there is considerable relationship between the pathogenesis of IBD and the neuro-endocrine-immune network. This article will describe the essential role of the neuro-immune-endocrine network in the development of IBD in terms of the hypothalamus-autonomic nervous system (HANS) axis, hypothalamic-pituitary-adrenal (HPA) axis and immunity.

The role of neuro-immune cross-talk in the regulation of inflammation and remodelling in asthma

Despite recent advances in the development of anti-asthmatic medication, asthma continues to be a major health problem worldwide. The symptoms of asthmatic patients include wheezing, chest tightness, cough and shortness of breath, which, together with airway hyperresponiveness, previously have been attributed to a dysfunction of airway nerves. However, research in the last two decades identified Th2-sensitization and the subsequent allergic reaction to innocuous environmental antigens as a basic immunological mechanism leading to chronic airway inflammation. Recent evidence suggests that the development of allergic asthma is influenced by events and circumstances in early childhood and even in utero. Allergen, ozone or stress exposure, as well as RSV infection in early life could be able to induce irreversible changes in the developing epithelial-mesenchymal trophic unit of the airways. The co-existence of chronic inflammation and neural dysfunction have recently drawn attention to the involvement of interaction pathways between the nervous and the immune system in the airways. Intensive basic research has accumulated morphological as well as functional evidence for the interaction between nerves and immune cells. Neuropeptides and neurotrophins have come into focus of attention as the key mediators of neuro-immune interactions, which lead to the development of several pharmacological compounds specifically targeting these molecules. This review will integrate our current knowledge on the involvement of neuro-immune pathways in asthma on the cellular and molecular level. It will summarize the results of pharmacological studies addressing the potential of neuropeptides and neurotrophins as novel therapeutic targets in asthma.

The airway cholinergic system: physiology and pharmacology

The present review summarizes the current knowledge of the cholinergic systems in the airways with special emphasis on the role of acetylcholine both as neurotransmitter in ganglia and postganglionic parasympathetic nerves and as non-neuronal paracrine mediator. The different cholinoceptors, various nicotinic and muscarinic receptors, as well as their signalling mechanisms are presented. The complex ganglionic and prejunctional mechanisms controlling the release of acetylcholine are explained, and it is discussed whether changes in transmitter release could be involved in airway dysfunctions. The effects of acetylcholine on different target cells, smooth muscles, nerves, surface epithelial and secretory cells as well as mast cells are described in detail, including the receptor subtypes involved in signal transmission.

Pharmacological properties of nicotinic acetylcholine receptors expressed by guinea pig small intestinal myenteric neurons

The electrophysiological and pharmacological properties of nicotinic acetylcholine receptors (nAChRs) were studied in guinea pig small intestinal myenteric neurons maintained in culture or in acutely isolated preparations. Acetylcholine and nicotine caused inward currents that desensitized in approximately 4 s. The current-voltage (I-V) relationship rectified inwardly with a reversal potential near 0 mV. The agonist rank order potency was 1,1-dimethyl-4-phenyl-piperazinium > acetylcholine = nicotine >> cytisine. Agonist-induced currents were blocked by nAChR antagonists with a rank order potency of mecamylamine > hexamethonium > dihydro-beta-erythroidine (DHbetaE); mecamylamine and DHbetaE exhibit high potency at beta4 and beta2 subunit-containing nAChRs, respectively. alpha-Bungarotoxin (0.1 microM) or alpha-methyllycaconitine (0.1 microM), antagonists that block nAChRs containing alpha7 subunits, did not affect acetylcholine-induced responses. Immunohistochemical studies revealed that nearly every neuron in culture was labeled by an antibody (mAb35) that recognizes nAChR alpha3 and alpha5 subunits. Antibodies selective for alpha3, alpha5, or beta2 subunits also stained most neurons, whereas an alpha7 subunit antibody revealed very few neurons. In neurons in the intact myenteric plexus from newborn and adult guinea pigs, local application of acetylcholine (1 mM) and cytisine (1 mM) caused similar amplitude depolarizations, and these responses were blocked by nAChR antagonists with a rank order potency of mecamylamine > hexamethonium > DHbetaE. These data indicate that myenteric neurons maintained in culture predominantly express nAChRs composed of alpha3, alpha5, beta2, and beta4 subunits. These subunits may be in a homogeneous population of receptors with unique pharmacological properties, or multiple receptors of different subunit composition may be expressed by individual neurons.

An electrophysiological study of muscarinic and nicotinic receptors of rat paratracheal ganglion neurons and their inhibition by Z-338

1. To study the mechanisms involved in the action of Z-338, a newly synthesized gastroprokinetic agent, experiments were performed with the paratracheal ganglion cells acutely dissociated from 2-week-old Wistar rats. The effects of Z-338 on both nicotinic and muscarinic responses of the ganglion cells were studied by nystatin perforated patch recording configuration under the current- and voltage-clamp conditions. 2. Acetylcholine (ACh) or nicotine, and muscarine or oxotremorine-M (OX-M) induced membrane depolarization with rapid and slow time courses respectively, followed by repetitive generation of action potentials in the ganglion cell. Corresponding to the membrane depolarization induced by cholinergic agents, ACh induced biphasic inward currents with rapid and slow time courses under the voltage-clamp condition. Nicotine and muscarine or OX-M evoked inward currents with rapid and slow time courses, respectively. The rapid and slow inward currents were accompanied by increase and decrease in the membrane conductance, respectively. In addition, OX-M dose-dependently suppressed the M-type K(+) current evoked in response to hyperpolarizing voltage-steps from V(H) of -25 mV to -50 mV, indicating that the activation of muscarinic acetylcholine receptors inhibits M-type K(+) current, thus inducing inward current in the ganglion cell. 3. Z-338 competitively suppressed the inward currents induced by OX-M through M(1) ACh receptor, and uncompetitively suppressed the currents induced by nicotine. 4. The inhibitory actions of Z-338 on the membrane depolarization and corresponding inward currents mediated by M(1)-muscarinic and neuronal nicotinic ACh receptors in the isolated ganglion cells were discussed in relation to the inhibitory actions on autoreceptors in the parasympathetic nerve terminals, which would explain the gastroprokinetic actions of Z-338.

Bradykinin activates airway parasympathetic ganglion neurons by inhibiting M-currents

The action of bradykinin on neurons acutely isolated from airway parasympathetic ganglia of rats and its mechanism were investigated using the nystatin-perforated patch-clamp recording technique. Under current clamp conditions, an application of 0.1 microM bradykinin onto rat airway ganglion neurons induced a depolarization which was accompanied by the action potential firing. Bradykinin elicited inward currents with decreasing the membrane conductance when a ganglion neuron was held at a holding potential of -40 mV. The half-maximum effective concentration was 8.9 nM. The bradykinin response was mimicked by a B(2) receptor agonist, [Hyp(3)]-bradykinin, and was inhibited by HOE-140, a B(2) antagonist, suggesting the contribution of B(2) receptors. The bradykinin-induced inward current reversed at the K(+) equilibrium potential, which shifted 56.5 mV with a 10-fold change in extracellular K(+) concentration. The application of 10(-3) M Ba(2+) induced the inward current, and bradykinin failed to evoke a further inward current in the presence of Ba(2+). Bradykinin also reduced the amplitude of M-current deactivation induced by a hyperpolarizing step from a holding potential of -25 mV to -50 mV with a half-maximum effective concentration of 16 nM. Pretreatment with pertussis toxin had no effect on the bradykinin-induced inhibition of the M-current. From these results we suggest that bradykinin may be able to depolarize the airway parasympathetic ganglion neurons of rats associated with an inhibition of M-type K(+) channels through the B(2) type of bradykinin receptors.

Activation of potassium conductance by ophiopogonin-D in acutely dissociated rat paratracheal neurones

1. The effect of ophiopogonin-D (OP-D), a steroidal glycoside and an active component of Bakumondo-to, a Chinese herbal antitussive, on neurones acutely dissociated from paratracheal ganglia of 2-week-old Wistar rats was investigated using the nystatin-perforated patch recording configuration. 2. Under current-clamp conditions, OP-D (10 microM) hyperpolarized the paratracheal neurones from a resting membrane potential of -65.7 to -73.5 mV. 3. At the concentration of 1 microM and above, OP-D concentration-dependently activated an outward current accompanied by an increase in the membrane conductance under voltage-clamp conditions at a holding potential of -40 mV. 4. The reversal potential of the OP-D-induced current (I(OP-D)) was -79.4 mV, which is close to the K(+) equilibrium potential of -86.4 mV. The changes in the reversal potential for a 10 fold change in extracellular K(+) concentration was 53.1 mV, indicating that the current was carried by K(+). 5. The I(OP-D) was blocked by an extracellular application of 1 mM Ba2+ by 59.0%, but other K(+) channel blockers, including 4-aminopyridine (3 mM), apamin (1 microM), charybdotoxin (0.3 microM), glibenclamide (1 microM), tolbutamide (0.3 mM) and tetraethylammonium (10 mM), did not inhibit the I(OP-D). 6. OP-D also inhibited the ACh- and bradykinin-induced depolarizing responses which were accompanied with firing of action potentials. 7. The results suggest that OP-D may be of benefit in reducing the excitability of airway parasympathetic ganglion neurones and consequently cholinergic control of airway function and further, that the hyperpolarizing effect of OP-D on paratracheal neurones via an activation of K(+) channels might explain a part of mechanisms of the antitussive action of the agent.

Are there functional P2X receptors on cell bodies in intact dorsal root ganglia of rats?

P2X purinoceptors have been suggested to participate in transduction of painful stimuli in nociceptive neurons. In the current experiments, ATP (1-10 mM), alpha,beta-methylene-ATP (10-30 microM) and capsaicin (10 nM-1 microM) were applied to neurons impaled with high resistance microelectrodes in rat dorsal root ganglia (L4 and L5) isolated in vitro together with the sciatic nerve and dorsal roots. The agonists were either bath applied or focally applied using a picospritzer. GABA (100 microM) and 40-80 mM K+ solutions gave brisk responses when applied by either technique. Only three of 22 neurons with slowly conducting axons (C cells) showed evidence of P2X-purinoceptor-mediated responses. Only two of 13 cells which responded to capsaicin (putative nociceptors), and none of 29 cells with rapidly conducting axons (A cells), responded to the purinergic agonists. When acutely dissociated dorsal root ganglion cells were studied using patch-clamp techniques, all but four of 30 cells of all sizes responded with an inward current to either ATP or alpha,beta-methylene-ATP (both 100 microM). Our data suggest that few sensory cell bodies in intact dorsal root ganglia express functional purinoceptors.

Monovalent and divalent cation permeability and block of neuronal nicotinic receptor channels in rat parasympathetic ganglia

Acetylcholine-evoked currents mediated by activation of nicotinic receptors in rat parasympathetic neurons were examined using whole-cell voltage clamp. The relative permeability of the neuronal nicotinic acetylcholine (nACh) receptor channel to monovalent and divalent inorganic and organic cations was determined from reversal potential measurements. The channel exhibited weak selectivity among the alkali metals with a selectivity sequence of Cs+ > K+ > Rb+ > Na+ > Li+, and permeability ratios relative to Na+ (Px/PNa) ranging from 1.27 to 0.75. The selectivity of the alkaline earths was also weak, with the sequence of Mg2+ > Sr2+ > Ba2+ > Ca2+, and relative permeabilities of 1.10 to 0.65. The relative Ca2+ permeability (PCa/PNa) of the neuronal nACh receptor channel is approximately fivefold higher than that of the motor endplate channel (Adams, D. J., T. M. Dwyer, and B. Hille. 1980. Journal of General Physiology. 75:493-510). The transition metal cation, Mn2+ was permeant (Px/PNa = 0.67), whereas Ni2+, Zn2+, and Cd2+ blocked ACh-evoked currents with half-maximal inhibition (IC50) occurring at approximately 500 microM, 5 microM and 1 mM, respectively. In contrast to the muscle endplate AChR channel, that at least 56 organic cations which are permeable to (Dwyer et al., 1980), the majority of organic cations tested were found to completely inhibit ACh-evoked currents in rat parasympathetic neurons. Concentration-response curves for guanidinium, ethylammonium, diethanolammonium and arginine inhibition of ACh-evoked currents yielded IC50's of approximately 2.5-6.0 mM. The organic cations, hydrazinium, methylammonium, ethanolammonium and Tris, were measureably permeant, and permeability ratios varied inversely with the molecular size of the cation. Modeling suggests that the pore has a minimum diameter of 7.6 A. Thus, there are substantial differences in ion permeation and block between the nACh receptor channels of mammalian parasympathetic neurons and amphibian skeletal muscle which represent functional consequences of differences in the primary structure of the subunits of the ACh receptor channel.

Acetylcholine-induced currents in acutely dissociated sympathetic neurons from adult hypertensive and normotensive rats have similar properties

Whole-cell patch-clamp recordings were used to compare the amplitude and kinetics of acetylcholine-induced currents (IACh) in acutely isolated superior cervical ganglion (SCG) neurons from spontaneously hypertensive (SHR) rats and Wistar-Kyoto (WKY) rats, to determine if altered postsynaptic transmitter responsiveness underlies the increased sympathetic nerve activity in SHR rat neurons. Rapidly activating and slowly inactivating inward currents were recorded in response to rapid application of ACh (5 microM to 2 mM). Concentration/response relationships for SCG neurons isolated for SHR and WKY rats had dissociation constants of 161 microM and 169 microM, maximum responses of 26 nS/pF and 24 nS/pF, and Hill coefficients of 1.8 and 1.9, respectively. Activation of the currents was fitted well by a single exponential function with concentration-dependent time constants, whereas inactivation was fitted well by a double exponential function also with concentration-dependent time constants. The time constants of both activation and inactivation for SHR and WKY rats were not significantly different at any concentration tested. The results demonstrate that the postsynaptic effects of ACh are similar between SHR and WKY rat postganglionic neurons and, therefore, probably do not contribute to the observed differences in ganglionic transmission between SHR and WKY rat nerves.

Nicotinic and muscarinic acetylcholine responses in the embryo chick ciliary ganglion cells

Nicotinic and muscarinic acetylcholine (ACh) responses were investigated in acutely dissociated chick ciliary ganglion neurons using the nystatin perforated patch clamp technique. ACh-induced a rapid transient inward current in 100% of the neurons at a holding potential of -60 mV. This rapid inward current was mimicked by nicotine but not by muscarine. The reversal potential of the rapid inward current was +10.5 mV and the current was inhibited by d-tubocurarine and hexamethonium in a dose-dependent manner. In 57.6% of neurons, a slow inward current was also induced by ACh at a holding potential of -20 mV. This slow inward current was mimicked by muscarine but not by nicotine. The slow inward current became smaller at a hyperpolarized potential but not reversed, being consistent with the fact that this current was elicited by the inhibition of M-current. p-Fluorohexa-hydrosiladifenidol (P-F-HHSiD) strongly inhibited the slow inward current, suggesting that the current was elicited by the activation of M3 receptors.

Nicotinic and muscarinic acetylcholine responses in differentiated PC12 cells

Nicotinic and muscarinic acetylcholine (ACh) responses were investigated in PC12 cells using the conventional whole-cell and nystatin perforated patch techniques. With the nystatin perforated patch, ACh induced three kinds of ionic currents: a rapid transient inward current, a subsequent transient outward current and a long-lasting slow inward current, whereas only a transient inward current was recorded by conventional whole-cell patch. The transient rapid inward current was mimicked by nicotine, but not by muscarine. On the contrary, the transient outward current and the long-lasting slow inward current were mimicked by muscarine but not by nicotine. Both nicotinic and muscarinic antagonists inhibited the transient inward current and the subsequent outward current in a concentration-dependent manner. The current-voltage relationship for the nicotine-induced transient current showed an inward rectification and the reversal potential was close to the Na+ equilibrium potential. The ACh-, muscarine-, CCh- and oxotremorine-M induced outward currents increased in a sigmoidal fashion with an increase in the concentration. Neither McN-A-343, an M1 agonist, nor oxotremorine, an M2 agonist, mimicked the muscarinic response. The reversal potential of the muscarinic response was close to the K+ equilibrium potential. The muscarinic response was not affected by pre-treatment with pertussis toxin but was enhanced by pre-treatment with Li+. In the cells perfused with Ca(2+)-free external solution, only the first application of ACh induced the muscarinic response. Calmodulin antagonists reversibly blocked the muscarinic response in a concentration-dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)

Voltage-dependent ionic currents in dissociated paratracheal ganglion cells of the rat

1. Conventional whole-cell voltage-clamp technique was used to study the electrophysiological and pharmacological properties of voltage-dependent Na+, K+ and Ca2+ channels in parasympathetic neurones enzymatically dissociated from the paratracheal ganglia of rat trachea. The voltage-dependent Na+, K+ and Ca2+ currents (INa, IK and ICa) were separated by the use of ion subtraction and pharmacological treatments. 2. INa was activated by a step depolarization more positive than -50 mV and fully activated at positive potentials more than +10 mV. The inactivation phase of INa consisted of fast and slow exponential components (tau if and tau is, respectively). The tau if and tau is were voltage dependent and decreased with a more positive step pulse. 3. The time course for recovery of INa from the complete inactivation exhibited two exponential processes. 4. The reversal potential of INa was equal to the Na+ equilibrium potential (ENa) and resembled a simple Na+ electrode depending only on external Na+ concentration. 5. Tetrodotoxin (TTX) reduced INa without affecting the current kinetics in a concentration-dependent manner, and the concentration of half-maximal inhibition (IC50) was 6 x 10(-9) M. There was no TTX-resistant component of INa in any of the cells tested. 6. Scorpion toxin increased the peak amplitude of INa and prolonged the inactivation phase in a time- and concentration-dependent manner. In the presence of toxin, both tau is and the fractional contribution of the slow current component to total INa increased concentration dependently. 7. High-threshold (L-type) ICa was activated by a step depolarization more positive than -30 mV and reached a peak at near 0 mV in the external solution with 2.5 mM Ca2+. The current was inactivated to only a small extent (< 10%) during 100 ms of depolarizing step pulse. There was no low-threshold (T-type) ICa in this preparation. 8. The maximum ICa in individual current-voltage (I-V) relationships was saturated by an increase in extracellular Ca2+ concentration ([Ca2+]o). The I-V relationships were also shifted along the voltage axis to the more positive potential with increasing [Ca2+]o. 9. The inactivation process of the L-type ICa was dependent on Ca2+ influxes (ICa-dependent inactivation). 10. Relative maximum peak currents of divalent cations passing through the L-type Ca2+ channels were in the order of IBa > ICa > ISr. 11. Organic and inorganic Ca2+ antagonists blocked the ICa in a concentration-dependent manner.(ABSTRACT TRUNCATED AT 400 WORDS)

Calcium permeability and modulation of nicotinic acetylcholine receptor-channels in rat parasympathetic neurons

Neuronal nicotinic acetylcholine (ACh)-activated currents in rat parasympathetic ganglion cells were examined using whole-cell and single-channel patch clamp recording techniques. The whole-cell current-voltage (I-V) relationship exhibited strong inward rectification and a reversal (zero current) potential of -3.9 mV in nearly symmetrical Na+ solutions (external 140 mM Na+/internal 160 mM Na+). Isosmotic replacement of extracellular Na+ with either Ca2+ or Mg2+ yielded the permeability (Px/PNa) sequence Mg2+ (1.1) > Na+ (1.0) > Ca2+ (0.65). Whole-cell ACh-induced current amplitude decreased as [Ca2+]0 was raised from 2.5 mM to 20 mM, and remained constant at higher [Ca2+]0. Unitary ACh-activated currents recorded in excised outside-out patches had conductances ranging from 15-35 pS with at least three distinct conductance levels (33 pS, 26 pS, 19 pS) observed in most patches. The neuronal nicotinic ACh receptor-channel had a slope conductance of 30 pS in Na+ external solution, which decreased to 20 pS in isotonic Ca2+ and was unchanged by isosmotic replacement of Na+ with Mg2+. ACh-activated single channel currents had an apparent mean open time (tau 0) of 1.15 +/- 0.16 ms and a mean burst length (tau b) of 6.83 +/- 1.76 ms at -60 mV in Na+ external solution. Ca(2+)-free external solutions, or raising [Ca2+]0 to 50-100 mM decreased both the tau 0 and tau b of the nAChR channel. Varying [Ca2+]0 produced a marked decrease in NP0, while substitution of Mg2+ for Na+ increased NP0. These data suggest that activation of the neuronal nAChR channel permits a substantial Ca2+ influx which may modulate Ca(2+)-dependent ion channels and second messenger pathways to affect neuronal excitability in parasympathetic ganglia.