Regulation of parasympathetic neurons by mast cells and histamine in the guinea pig heart

Autonomic nervous system receptor-mediated regulation of mast cell degranulation modulates the inflammation after corneal epithelial abrasion

Mast cells (MCs) regulate wound healing and are influenced by the autonomic nervous system (ANS). However, the underlying mechanisms affecting wound healing outcomes remain elusive. Here, we explored the specific role of the ANS by regulating MC degranulation following corneal epithelium abrasion. A mouse model of corneal abrasion was established by mechanically removing a 2-mm central epithelium. Wound closure, neutrophil infiltration, and transcription of injured corneas were investigated using whole-mount immunostaining, flow cytometry, and RNA-sequencing analysis, respectively. Inhibition of MC degranulation by the MC stabilizers cromolyn sodium and lodoxamide tromethamine increased the infiltration of neutrophils and delayed healing of abraded corneas. Moreover, transcriptomic profiling analysis showed that purified MCs from the limbus expressed adrenergic and cholinergic receptors. Pharmacological manipulation and sympathectomy with 6-hydroxydopamine confirmed that sympathetic nervous system signaling inhibited MC degranulation after corneal abrasion, whereas parasympathetic nervous system signaling enhanced MC degranulation. We conclude that normal degranulation of MCs in the corneal limbus and crosstalk between the ANS and MCs are crucial for the appropriate control of inflammation and the repair progress of wounded corneas. This suggests a potential approach for improving defective corneal wound healing by the administration of clinically available autonomic activity-modulating agents.

Beclomethasone dipropionate and sodium cromoglycate protect against airway hyperresponsiveness in a human ex vivo model of cow's milk aspiration

Background

Recurrent cow's milk (CM) aspiration is often associated with gastroesophageal reflux in infants and toddlers and it seems to be implicated in the etiology of different inflammatory lung disorders. This study aimed to investigate ex vivo the impact of CM aspiration on human airways and whether treatment with beclomethasone dipropionate (BDP) or sodium cromoglycate (SCG) may prevent the potential CM-induced airway hyperresponsiveness (AHR).

Methods

Human isolated bronchi were contracted by electrical field stimulation (EFS_10Hz) to mimic the contractile tone induced by the parasympathetic activity and challenged with CM, fat/lactose-free CM, or human breast milk (HM). The effect of pre-treatment with beclomethasone dipropionate (BDP) and sodium cromoglycate (SCG) was also investigated on the AHR induced by CM.

Results

After a 60 min-challenge with CM 1:10 v/v and fat/lactose-free CM 1:10 v/v, ASM significantly (P ​< ​0.05) increased compared to control (+67.04 ​± ​17.08% and +77.91 ​± ​1.34%, respectively), a condition that remained stable for 150 ​min post-treatment, whereas HM did not alter ASM contractility. BDP 1 ​μM and 10 ​μM significantly (P ​< ​0.05) reduced the AHR elicited by CM (−52.49 ​± ​10.97% and −66.98 ​± ​7.90%, respectively vs. control). At the same manner, SCG 1 ​μM and 10 ​μM significantly (P ​< ​0.05) inhibited the CM-induced AHR (−59.03 ​± ​9.24% and −73.52 ​± ​7.41%, respectively vs. control).

Conclusion

CM induces AHR in human ASM by eliciting an increased parasympathetic contractile response. Preventive treatment with nebulized SCG may be indicated in infants or toddlers fed with CM, rather than with BDP due to a superior safety profile.

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Cow's milk aspiration seems to be associated with some inflammatory lung diseases.

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Cow's milk aspiration induces human airway hyperresponsiveness.

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Beclomethasone and sodium cromoglycate protect against cow's milk hyperresponsiveness in vitro.

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Inhaled sodium cromoglycate might be suitable in children at risk of cow's milk aspiration.

The role of the tripartite synapse in the heart: how glial cells may contribute to the physiology and pathophysiology of the intracardiac nervous system

One of the major roles of the intracardiac nervous system (ICNS) is to act as the final site of signal integration for efferent information destined for the myocardium to enable local control of heart rate and rhythm. Multiple subtypes of neurons exist in the ICNS where they are organized into clusters termed ganglionated plexi (GP). The majority of cells in the ICNS are actually glial cells; however, despite this, ICNS glial cells have received little attention to date. In the central nervous system, where glial cell function has been widely studied, glia are no longer viewed simply as supportive cells but rather have been shown to play an active role in modulating neuronal excitability and synaptic plasticity. Pioneering studies have demonstrated that in addition to glia within the brain stem, glial cells within multiple autonomic ganglia in the peripheral nervous system, including the ICNS, can also act to modulate cardiovascular function. Clinically, patients with atrial fibrillation (AF) undergoing catheter ablation show high plasma levels of S100B, a protein produced by cardiac glial cells, correlated with decreased AF recurrence. Interestingly, S100B also alters GP neuron excitability and neurite outgrowth in the ICNS. These studies highlight the importance of understanding how glial cells can affect the heart by modulating GP neuron activity or synaptic inputs. Here, we review studies investigating glia both in the central and peripheral nervous systems to discuss the potential role of glia in controlling cardiac function in health and disease, paying particular attention to the glial cells of the ICNS.

Histamine depolarizes rat intracardiac ganglion neurons through the activation of TRPC non-selective cation channels

The cardiac plexus, which contains parasympathetic ganglia, plays an important role in regulating cardiac function. Histamine is known to excite intracardiac ganglion neurons, but the underlying mechanism is obscure. In the present study, therefore, the effect of histamine on rat intracardiac ganglion neurons was investigated using perforated patch-clamp recordings. Histamine depolarized acutely isolated neurons with a half-maximal effective concentration of 4.5 μM. This depolarization was markedly inhibited by the H₁ receptor antagonist triprolidine and mimicked by the H₁ receptor agonist 2-pyridylethylamine, thus implicating histamine H₁ receptors. Consistently, reverse transcription-PCR (RT-PCR) and Western blot analyses confirmed H₁ receptor expression in the intracardiac ganglia. Under voltage-clamp conditions, histamine evoked an inward current that was potentiated by extracellular Ca²⁺ removal and attenuated by extracellular Na⁺ replacement with N-methyl-D-glucamine. This implicated the involvement of non-selective cation channels, which given the link between H₁ receptors and G_q/11-protein-phospholipase C signalling, were suspected to be transient receptor potential canonical (TRPC) channels. This was confirmed by the marked inhibition of the inward current through the pharmacological disruption of either G_q/11 signalling or intracellular Ca²⁺ release and by the application of the TRPC blockers Pyr3, Gd³⁺ and ML204. Consistently, RT-PCR analysis revealed the expression of several TRPC subtypes in the intracardiac ganglia. Whilst histamine was also separately found to inhibit the M-current, the histamine-induced depolarization was only significantly inhibited by the TRPC blockers Gd³⁺ and ML204, and not by the M-current blocker XE991. These results suggest that TRPC channels serve as the predominant mediator of neuronal excitation by histamine.

Mast Cells: Key Contributors to Cardiac Fibrosis

Historically, increased numbers of mast cells have been associated with fibrosis in numerous cardiac pathologies, implicating mast cells in the development of cardiac fibrosis. Subsequently, several approaches have been utilised to demonstrate a causal role for mast cells in animal models of cardiac fibrosis including mast cell stabilising compounds, rodents deficient in mast cells, and inhibition of the actions of mast cell-specific proteases such as chymase and tryptase. Whilst most evidence supports a pro-fibrotic role for mast cells, there is evidence that in some settings these cells can oppose fibrosis. A major gap in our current understanding of cardiac mast cell function is identification of the stimuli that activate these cells causing them to promote a pro-fibrotic environment. This review will present the evidence linking mast cells to cardiac fibrosis, as well as discuss the major questions that remain in understanding how mast cells contribute to cardiac fibrosis.

Angiotensin II potentiates adrenergic and muscarinic modulation of guinea pig intracardiac neurons

The intrinsic cardiac plexus represents a major peripheral integration site for neuronal, hormonal, and locally produced neuromodulators controlling efferent neuronal output to the heart. This study examined the interdependence of norepinephrine, muscarinic agonists, and ANG II, to modulate intrinsic cardiac neuronal activity. Intracellular voltage recordings from whole-mount preparations of the guinea pig cardiac plexus were used to determine changes in active and passive electrical properties of individual intrinsic cardiac neurons. Application of either adrenergic or muscarinic agonists induced changes in neuronal resting membrane potentials, decreased afterhyperpolarization duration of single action potentials, and increased neuronal excitability. Adrenergic responses were inhibited by removal of extracellular calcium ions, while muscarinic responses were inhibited by application of TEA. The adrenergic responses were heterogeneous, responding to a variety of receptor-specific agonists (phenylephrine, clonidine, dobutamine, and terbutaline), although α-receptor agonists produced the most frequent responses. Application of ANG II alone produced a significant increase in excitability, while application of ANG II in combination with either adrenergic or muscarinic agonists produced a much larger potentiation of excitability. The ANG II-induced modulation of firing was blocked by the angiotensin type 2 (AT(2)) receptor inhibitor PD 123319 and was mimicked by the AT(2) receptor agonist CGP-42112A. AT(1) receptor blockade with telmasartin did not alter neuronal responses to ANG II. These data demonstrate that ANG II potentiates both muscarinically and adrenergically mediated activation of intrinsic cardiac neurons, doing so primarily via AT(2) receptor-dependent mechanisms. These neurohumoral interactions may be fundamental to regulation of neuronal excitability within the intrinsic cardiac nervous system.

Remodeling of the guinea pig intrinsic cardiac plexus with chronic pressure overload

Chronic pressure overload (PO) is associated with cardiac hypertrophy and altered autonomic control of cardiac function, in which the latter may involve adaptations in central and/or peripheral cardiac neural control mechanisms. To evaluate the specific remodeling of the intrinsic cardiac nervous system following pressure overload, the descending thoracic aorta artery of the guinea pig was constricted approximately 20%, and the animals recovered for 9 wk. Thereafter, atrial neurons of the intrinsic cardiac plexus were isolated for electrophysiological and immunohistochemical analyses. Intracellular voltage recordings from intrinsic cardiac neurons demonstrated no significant changes in passive membrane properties or action potential depolarization compared with age-matched controls and sham-operated animals, but afterhyperpolarization duration was increased in PO animals. Neuronal excitability, as determined by the number of action potentials produced with depolarizing stimuli, was differentially increased in phasic neurons derived from PO animals in response to exogenously applied histamine compared with sham and age-matched controls. Conversely, pituitary adenylate cyclase-activating polypeptide-induced increases in intrinsic cardiac neuron evoked AP frequency were similar between control and PO animals. Immunohistochemical analysis demonstrated a twofold increase in the percentage of neurons immunoreactive for neuronal nitric oxide synthase in PO animals compared with control. The density of mast cells within the intrinsic cardiac plexus from PO animals was also increased twofold compared with preparations from control animals. These results indicate that congestive heart failure associated with chronic pressure overload induces a differential remodeling of intrinsic cardiac neurons and upregulation of neuronal responsiveness to specific neuromodulators.

Cooperation between mast cells and neurons is essential for antigen-mediated bronchoconstriction

Mast cells are important sentinels guarding the interface between the environment and the body: a breach in the integrity of this interface can lead to the release of a plethora of mediators that engage the foreign agent, recruit leukocytes, and initiate adaptive physiological changes in the organism. While these capabilities make mast cells critical players in immune defense, it also makes them important contributors to the pathogenesis of diseases such as asthma. Mast cell mediators induce dramatic changes in smooth muscle physiology, and the expression of receptors for these factors by smooth muscle suggests that they act directly to initiate constriction. Contrary to this view, we show herein that mast cell-mediated bronchoconstriction is observed only in animals with intact innervation of the lung and that serotonin release alone is required for this action. While ablation of sensory neurons does not limit bronchoconstriction, constriction after Ag challenge is absent in mice in which the cholinergic pathways are compromised. Linking mast cell function to the cholinergic system likely provides an important means of modulating the function of these resident immune cells to physiology of the lung, but may also provide a safeguard against life-threatening anaphylaxis during mast cell degranulation.

Chronic myocardial infarction induces phenotypic and functional remodeling in the guinea pig cardiac plexus

Chronic myocardial infarction (CMI) is associated with remodeling of the ventricle and evokes adaption in the cardiac neurohumoral control systems. To evaluate the remodeling of the intrinsic cardiac nervous system following myocardial infarction, the dorsal descending coronary artery was ligated in the guinea pig heart and the animals were allowed to recover for 7-9 wk. Thereafter, atrial neurons of the intrinsic cardiac plexus were isolated for electrophysiological and immunohistochemical analyses. Intracellular voltage recordings from intrinsic cardiac neurons demonstrated no significant changes in passive membrane properties or action potential configuration compared with age-matched controls and sham-operated animals. The intrinsic cardiac neurons from chronic infarcted hearts did demonstrate an increase in evoked action potential (AP) frequency (as determined by the number of APs produced with depolarizing stimuli) and an increase in responses to exogenously applied histamine compared with sham and age-matched controls. Conversely, pituitary adenylate cyclase-activating polypeptide (PACAP)-induced increases in intrinsic cardiac neuron-evoked AP frequency were similar between control and CMI animals. Immunohistochemical analysis demonstrated a threefold increase in percentage of neurons immunoreactive for neuronal nitric oxide synthase (NOS) in CMI animals compared with control and the additional expression of inducible NOS by some neurons, which was not evident in control animals. Finally, the density of mast cells within the intrinsic cardiac plexus was increased threefold in preparations from CMI animals. These results indicate that CMI induces a differential remodeling of intrinsic cardiac neurons and functional upregulation of neuronal responsiveness to specific neuromodulators.

Wide distribution and subcellular localization of histamine in sympathetic nervous systems of different species

Previous studies have demonstrated that histamine (HA) acts as a neurotransmitter in the cardiac sympathetic nervous system of the guinea pig. The aim of the current study was to examine whether HA widely exists in the sympathetic nervous systems of other species and the subcellular localization of HA in sympathetic terminals. An immunofluorescence histochemical multiple-staining technique and anterograde tracing method were employed to visualize the colocalization of HA and norepinephrine (NE) in sympathetic ganglion and nerve fibers in different species. Pre-embedding immunoelectron microscopy was used to observe the subcellular distribution of HA in sympathetic nerve terminals. Under the confocal microscope, coexistence of NE and HA was displayed in the superior cervical ganglion and celiac ganglion neurons of the mouse and dog as well as in the vas deferens, mesenteric artery axon, and varicosities of the mouse and guinea pig. Furthermore, colocalization of NE and HA in cardiac sympathetic axons and varicosities was labeled by biotinylated dextranamine injected into the superior cervical ganglion of the guinea pig. By electron microscopy, HA-like high-density immunoreactive products were seen in the small vesicles of the guinea pig vas deferens. These results provide direct cellular and subcellular morphological evidence for the colocalization of HA and NE in sympathetic ganglion and nerve fibers, and support that HA is classified as a neurotransmitter in sympathetic neurons.

Mast cell degranulation alters lymphatic contractile activity through action of histamine

OBJECTIVE

Mast cells reside in most tissues and in close association with blood vessels and nerves, areas where lymphatic vessels are also present. Mast cells and lymphatic vessels are two important players in the development of the inflammatory process. This study was designed to examine the effects of mast cell degranulation on the contractile activity of mesenteric lymphatic vessels.

METHODS

Lymphatic vessel contractile activity was assessed in vitro by video microscopy of the mesentery of cow's milk-sensitized guinea pigs upon application of beta-lactoglobulin and compared to the response measured in sham animals.

RESULTS

Application of 5-10 microM beta-lactoglobulin increased lymphatic vessel constriction frequency and decreased constriction amplitude (n = 12). This effect was not seen in sham-treated animals (n = 16) and was not due to an increased number of mast cells in the mesentery of the milk-sensitized animals, as revealed by histological examination. Two known mast cell-derived mediators, histamine and thromboxane A2, via stable mimetic U46619 also altered lymphatic pumping in a similar manner, but only pretreatment with the histamine H1 receptor antagonist pyrilamine (1 microM) could reduce the beta-lactoglobulin-induced response. The thromboxane A2 receptor antagonist, SQ 29548, and the 5-lipoxygenase inhibitor, caffeic acid, were without significant effect.

CONCLUSION

In the in vitro mesenteric preparation, mast cell degranulation altered lymphatic contractile activity via the release of a mediator suggested to be histamine and the subsequent activation of H1 receptors. This action could potentially interfere with the expected ability of lymphatic vessels to reduce edema during inflammation.

Ionic mechanisms of histamine-induced responses in guinea pig intracardiac neurons

Histamine, released from mast cells, can modulate the activity of intrinsic neurons in the guinea pig cardiac plexus. The present study examined the ionic mechanisms underlying the histamine-induced responses in these cells. Histamine evokes a small membrane depolarization and an increase in neuronal excitability. Using intracellular voltage recording from individual intracardiac neurons, we were able to demonstrate that removal of extracellular sodium reduced the membrane depolarization, whereas inhibition of K+ channels by 1 mM Ba2+, 2 mM Cs+, or 5 mM tetraethylammonium had no effect. The depolarization was also not inhibited by either 10 μM Gd3+ or a reduced Cl− solution. The histamine-induced increase in excitability was unaffected by K+ channel inhibitors; however, it was reduced by either blockage of voltage-gated Ca2+ channels with 200 μM Cd2+ or replacement of extracellular Ca2+ with Mg2+. Conversely, alterations in intracellular calcium with thapsigargin or caffeine did not inhibit the histamine-induced effects. However, in cells treated with both thapsigargin and caffeine to deplete internal calcium stores, the histamine-induced increase in excitability was decreased. Treatment with the phospholipase C inhibitor U73122 also prevented both the depolarization and the increase in excitability. From these data, we conclude that histamine, via activation of H1 receptors, activates phospholipase C, which results in 1) the opening of a nonspecific cation channel, such as a transient receptor potential channel 4 or 5; and 2) in combination with either the influx of Ca2+ through voltage-gated channels or the release of internal calcium stores leads to an increase in excitability.

The protective effect of H2-receptor activation against the duration of myocardial hypoxia/reoxygenation-induced ventricular fibrillation in sensitized guinea-pig hearts

Patients with high serum immunoglobulin E levels were reported to be protected against sudden death during acute myocardial infarction. The protection mechanism might be attributed to the facilitation of histamine release from sensitized mast cells; however, this remains to be clarified. In this study, we examined the influence of sensitization on ventricular fibrillation (VF) induced by myocardial hypoxia/reoxygenation (H/R). Guinea pigs were actively sensitized by subcutaneous injection of ovalbumin in Bordetella pertussis vaccine. Hearts isolated from non-sensitized and sensitized guinea pigs were subjected to 30-min hypoxia / 30-min reoxygenation using a Langendorff apparatus. The amount of histamine released in the sensitized guinea-pig hearts was elevated, and the duration of VF was found to be reduced. The treatment with a histamine H2-receptor antagonist inhibited the reduction of VF duration. Treatment of the non-sensitized hearts with the histamine H2-receptor agonist resulted in the decrease of VF duration to the same level as that in the sensitized hearts. In conclusion, these results suggest that the risk of sudden death during myocardial H/R may be attenuated in the sensitized hearts and that histamine H2-receptor activation due to the released histamine may be involved in the protective effect.

Mast cells modulate maintained neuronal activity in the thalamus in vivo

Single cell unit activity of 187 neurons of 24 rats were analysed to study the possible involvement of intracranial mast cells on modifying thalamic neuronal activity. Mast cells were activated with microiontophoretical application of compound 48/80. This substance did not modify the firing rate of cortical or hippocampal neurons (no mast cells are found here), however it caused excitation (70% in females, 11% in males), or inhibition (7% in females, 33% in males) on thalamic neurons, possibly due to mast cell activation. In consecutive anatomical evaluation many partially or fully degranulated mast cells were found in the recorded thalamic areas.

Interrelationships Between the Autonomic Nervous System and Atrial Fibrillation

Mechanisms responsible for atrial fibrillation are not completely understood but the autonomic nervous system is a potentially potent modulator of the initiation, maintenance, termination and ventricular rate determination of atrial fibrillation. Complex interactions exist between the parasympathetic and sympathetic nervous systems on the central, ganglionic, peripheral, tissue, cellular and subcellular levels that could be responsible for alterations in conduction and refractoriness properties of the heart as well as the presence and type of triggered activity, all of which could contribute to atrial fibrillation. These dynamic inter-relationships may also be altered dependent upon other neurohumoral modulators and cardiac mechanical effects from ventricular dysfunction and congestive heart failure. The clinical implications regarding the effects of the autonomic nervous system in atrial fibrillation are widespread. The effects of modulating ganglionic input into the atria may alter the presence or absence of atrial fibrillation as has been highlighted from ablation investigations. This article reviews what is known regarding the inter-relationships between the autonomic nervous system and atrial fibrillation and provides state of the art information at all levels of autonomic interactions.

Tachykinin Agonists Modulate Cholinergic Neurotransmission at Guinea-Pig Intracardiac Ganglia

Effects of substance P (SP) and selective tachykinin agonists on neurotransmission at guinea-pig intracardiac ganglia were studied in vitro. Voltage responses of neurons to superfused tachykinins and nerve stimulation were measured using intracellular microelectrodes. Predominant effects of SP (1 microM) were to cause slow depolarization and enable synaptic transmission at low intensities of nerve stimulation. Augmented response to nerve stimulation occurred with 29 of 40 intracardiac neurons (approx. 73%). SP inhibited synaptic transmission at 23% of intracardiac neurons but also caused slow depolarization. Activation of NK(3) receptors with 100 nM [MePhe(7)]neurokinin B caused slow depolarization, enhanced the response of many intracardiac neurons to low intensity nerve stimulation or local application of acetylcholine, and triggered action potentials independent of other stimuli in 6 of 42 neurons. The NK(1) agonist [Sar(9),Met(O(2))(11)]SP had similar actions but was less effective and did not trigger action potentials independently. Neither selective agonist inhibited cholinergic neurotransmission. We conclude that SP can function as a positive or negative neuromodulator at intracardiac ganglion cells, which could be either efferent neurons or interneurons. Potentiation occurs primarily through NK(3) receptors and may enable neuronal responses with less preganglionic nerve activity. Inhibition of neurotransmission by SP is most likely explained by the known blocking action of this peptide at ganglionic nicotine receptors.

Co-localization of histamine and dopamine-beta-hydroxylase in sympathetic ganglion and release of histamine from cardiac sympathetic terminals of guinea-pig

1. The aim of this study was to investigate the co-localization of histamine and dopamine-beta-hydroxylase in the superior cervical ganglion of guinea-pig and release of histamine from cardiac sympathetic terminals in guinea-pig isolated atrium. 2. Histidine decarboxylase (a histamine-synthesizing enzyme) mRNA signals were detected in the neurones of superior cervical ganglion of guinea-pig by in situ hybridization. The results of double-labelled immunofluorescence further confirmed the co-localization of histamine and dopamine-beta-hydroxylase in the large principle neurons and small intensely fluorescent cells in the superior cervical ganglion. The immunoreactivities of both histamine and dopamine-beta-hydroxylase were significantly attenuated after 6-hydroxydopamine-induced lesion of sympathetic nerves. 3. The refractory electrical field stimulation caused the release of histamine from cardiac sympathetic terminals of guinea-pig isolated atria (112.14 +/- 40.34 ng x ml(-1)), which was significantly attenuated to 35 +/- 15.57 ng x ml(-1) by reserpine pretreatment. Following administering compound 48/80, a mast cell degranulator, electrical field stimulation induced a dramatic increase of endogenous histamine release from isolated atria (303.57 +/-72.93 ng x ml(-1)). When compound 48/80 was added to the reserpine-treated atria, the release of histamine induced by field stimulation was decreased to 207.14 +/- 76.39 ng x ml(-1). 4 These results provide novel evidence that histamine co-exists with noradrenaline in sympathetic nerves and might act as a neurotransmitter to modulate sympathetic neurotransmission.

Modulation of guinea pig intrinsic cardiac neurons by prostaglandins

Activation of cardiac mast cells has been shown to alter parasympathetic neuronal function via the activation of histamine receptors. The present study examined the ability of prostaglandins to alter the activity of guinea pig intracardiac neurons. Intracellular voltage recordings from whole mounts of the cardiac plexus showed that antigen-mediated mast cell degranulation produces an attenuation of the afterhyperpolarization (AHP), which was prevented by the phospholipase A2 inhibitor 5,8,11,14-eicosatetraynoic acid. Exogenous application of either PGD2 or PGE2 produced a biphasic change in the membrane potential and an inhibition of both AHP amplitude and duration. Examination of prostanoid receptors using bath perfusions (1 microM PGE2 and PGD2), specific agonists (BW245C, sulprostone, and butaprost), and antagonists (AH6809 and SC19220) found evidence for both the PGE2-specific EP2 and EP3 receptors, but not for EP1 or the PGD2-specific prostanoid (DP) receptors. Sulprostone was able to mimic the PGE2 responses in some cells, but not in all PGE2-sensitive cells. Butaprost was able to mimic the PG-induced hyperpolarization in some cells, but did not alter the AHP. Inhibition of specific potassium channels with either TEA, charybdotoxin, or apamin showed that neither TEA nor charybdotoxin could prevent the PGE2-induced AHP attenuation. Apamin alone inhibited AHP duration, with PGs having no further effect in these cells. These results demonstrate that guinea pig intracardiac neurons can be modulated by PG, most likely through either EP2, EP3, or potentially EP4 receptors, and this response is due, at least in part, to a reduction in small-conductance KCa currents.

Electron microscopic study of intrinsic cardiac ganglia in the adult human

The aim of the present study was to describe in detail the ultrastructure of intrinsic cardiac ganglionic cells in the healthy human as these cells appear to be directly involved in the development of tachycardia, atrioventricular block, ventricular fibrillation, and sudden cardiac death. Tissues examined in this study were obtained from hearts of 10 adult humans of either sex aged 22-80 years at autopsy performed no more than 8 h after death. The examined human intrinsic cardiac nerve cells were in most respects typical autonomic neurons surrounded by a sheath of satellite cells that was either uni- or multilayered. In addition to regular unmyelinated axons, prominent large axon terminals containing lamellated dense bodies, mitochondria and vesicles in the cytoplasm were observed in the ganglion neuropil. Synaptic profiles were more common in the ganglion neuropil than on neuronal somata. According to axon terminal contents, synaptic profiles were of three types. The most common Type 1 synaptic profiles contained a predominance of small clear, with a few larger dense-cored vesicles and mitochondria. Type 2 synaptic profiles, in addition to the same components as in Type 1, had glycogen-like particles. Type 3 vesicle-containing profiles clearly differed from both the previous ones as they were the largest in diameter and included plentifiul large clear pleomorphic or dense-cored vesicles together with small clear and larger dense-cored vesicles, mitochondria, dense and multivesicular bodies. Independently of age of the human, the most frequent neuronal abnormality was an abundant accumulation of inclusions inside of somata and dendrites that, in profile, appeared like circular membranous or fine granular bodies variable in electron density. In addition to inclusions, some neuronal somata and dendrites had strongly swollen mitochondria filled up with granular material in spite of their close association with normal looking ganglionic neurons. Structures resembling an axon growth cone in profile were revealed inside of cardiac ganglia derived from an 80 year old man. In conclusion, the present results provide baseline information on the normal ultrastructure of intracardiac ganglia in healthy humans which may be useful for assessing and interpreting the degree of damage of ganglionic cells both in autonomic and sensory neuropathies of the human heart.