Role of nitric oxide in non-adrenergic, non-cholinergic relaxation and modulation of excitatory neuroeffector transmission in the cat airway

The Inhibitory Mechanism of Gentamicin on Electrical Field Stimulation Response in Rat Bladder Smooth Muscle

To see the inhibitory mechanism of gentamicin in response to electrical field stimulation (EFS) using the rat bladder smooth muscle, atropine or guanethidine was treated but had no effect. Methylsergide, a non-selective 5-HT1, 5-HT2 receptor antagonist was also treated but had on effect. Kinase inhibitors, such as chelerythrine (PKC inhibitor), ML-9 (MLCK inhibitor), or Y27632 (rho kinase inhibitor) were pretreated before gentamicin treatment, but did not have effect. For U73122, a phospholipase C (PLC) inhibitor however, the inhibitory effect to gentamicin was significantly attenuated in all frequencies given by the EFS. Therefore gentamicin induced inhibitory effect on EFS response in rat bladder smooth muscle was not mediated by the activation of adrenergic, cholinergic, or serotonergic receptor. The inhibition of gentamicin might be mediated through the PLC dependent pathway, but not through the PKC, MLCK or rho kinase dependent pathway.

Effects of intravenous and subcutaneous heartworm homogenate from doxycycline-treated and untreated donor dogs on bronchial reactivity and lung in cats

A controlled, blind research study was conducted to define the innate response of lungs in specific pathogen free (SPF) cats to intravenous (n=10) or subcutaneous (n=4) administration of homogenate of adult Dirofilaria immitis from donor dogs compared with lung response in control cats (n=6). There was no difference in cats that received heartworm homogenate IV for 18 days from donor dogs treated with doxycycline for 1 month compared with cats given heartworm homogenate from untreated donor dogs. Cats did not develop clinical signs, and no radiographic changes were noted. Cats given SC heartworm homogenate at lower concentration than IV groups did not develop histologic changes. Cats that received IV heartworm homogenate for 18 days developed mild interstitial and peribronchial myofibrocyte proliferation and smooth muscle proliferation of the pulmonary arteries. Bronchial ring contractility in vitro was blunted in the IV homogenate cats to the agonists acetylcholine and 5-hydroxytryptamine. Cats in the SC group had increased sensitivity to histamine at high concentrations but normal contractility and relaxation responses to other agonists. No increase in mast cells was noted in lung tissues of cats given homogenate. In the absence of bronchial wall remodeling, cats given IV homogenate had blunted responses to bronchial constriction, but normal relaxation to nitroprusside and substance P and increased sensitivity to histamine. In the absence adult heartworms, the homogenate of adult heartworms in the circulation of SPF cats induced a direct effect on lung parenchyma and altered bronchial ring reactivity.

Asthma in humans and cats: is there a common sensitivity to aeroallegens in shared environments?

Cats spontaneously develop eosinophilic airway inflammation and airway hyperreactivity that is very similar to human allergic asthma. In addition, household cats share environmental exposures to aeroallergens with humans. We review the scientific literature concerning the pathophysiology of feline asthma, including similarities to human asthma and evidence regarding environmental aeroallergen triggers. Results of pathophysiological studies suggest important similarities between human and feline responses to inhaled allergens. Only a few studies were found that examined the development of disease in cats to environmental aeroallergens. Limited evidence suggests that some environmental allergens can cause disease in both cats and humans. It appears that there is a need for greater communication between human and animal health professionals regarding environmental causes of asthma. Specifically, additional research into linkages between human and feline asthma using both molecular techniques and clinical epidemiological approaches could lead to improved understanding of the environmental risks. Finally, there should be consideration of use of naturally affected and/or experimentally induced (using clinically relevant allergens) asthmatic cats in preclinical trials for novel therapeutic interventions.

feG-COOH blunts eosinophilic airway inflammation in a feline model of allergic asthma

OBJECTIVE AND DESIGN

This study investigated if feG-COOH would decrease allergen-induced airway inflammation.

MATERIALS OR SUBJECTS

Seven adult cats sensitised to Bermuda grass allergen (BGA) to induce an asthmatic phenotype.

TREATMENT

Cats were randomized to receive either feG-COOH (1 mg/kg, PO) or placebo (saline 1 ml, PO) immediately prior to BGA aerosol challenge in a cross-over design.

METHODS

Bronchoalveolar lavage fluid (BALF) was collected and airway inflammatory response assessed via inflammatory cell number and type; IL-4, IFN-gamma and nitric oxide metabolite concentrations. A paired t test was used to compare parameters with a P < 0.05 considered significant.

RESULTS

The BALF eosinophil percentage was significantly lower in asthmatic cats treated with feG compared with placebo (placebo, 35.3 +/- 12.2%; feG, 22.4 +/- 8.6%; P = 0.002). Treatment with feG did not result in a significant change in any other parameter measured.

CONCLUSIONS

These data indicate that a single dose of feG-COOH partially attenuates eosinophilic airway inflammation in experimental feline asthma.

Airway smooth muscle relaxation induced by 5-HT(2A) receptors: role of Na(+)/K(+)-ATPase pump and Ca(2+)-activated K(+) channels

AIMS

Although 5-hydroxytryptamine (5-HT) contracts airway smooth muscle in many mammalian species, in guinea pig and human airways 5-HT causes a contraction followed by relaxation. This study explored potential mechanisms involved in the relaxation induced by 5-HT.

MAIN METHODS

Using organ baths, patch clamp, and intracellular Ca(2+) measurement techniques, the effect of 5-HT on guinea pig airway smooth muscle was studied.

KEY FINDINGS

A wide range of 5-HT concentrations caused a biphasic response of tracheal rings. Response to 32 microM 5-HT was notably reduced by either tropisetron or methiothepin, and almost abolished by their combination. Incubation with 10 nM ketanserin significantly prevented the relaxing phase. Likewise, incubation with 100 nM charybdotoxin or 320 nM iberiotoxin and at less extent with 10 microM ouabain caused a significant reduction of the relaxing phase induced by 5-HT. Propranolol, L-NAME and 5-HT(1A), 5-HT(1B)/5-HT(1D) and 5-HT(2B) receptors antagonist did not modify this relaxation. Tracheas from sensitized animals displayed reduced relaxation as compared with controls. In tracheas precontracted with histamine, a concentration response curve to 5-HT (32, 100 and 320 microM) induced relaxation and this effect was abolished by charybdotoxin, iberiotoxin or ketanserin. In single myocytes, 5-HT in the presence of 3 mM 4-AP notably increased the K(+) currents (I(K(Ca))), and they were completely abolished by charybdotoxin, iberiotoxin or ketanserin.

SIGNIFICANCE

During the relaxation induced by 5-HT two major mechanisms seem to be involved: stimulation of the Na(+)/K(+)-ATPase pump, and increasing activity of the high-conductance Ca(2+)-activated K(+) channels, probably via 5-HT(2A) receptors.

A pilot study of nitric oxide blood levels in patients with chronic orofacial pain

BACKGROUND

Control of pain is the major goal in the management of chronic orofacial pain (COP) patients. The pathogenesis of COP is currently not well understood. Consequently, the treatment of COP may be suboptimal or even harmful. Based on independent observations, we propose that local elevated levels of nitric oxide (NO) may have a central role in the pathogenesis of COP.

HYPOTHESIS

NO level in the orofacial region of COP patients is elevated. A regional increased level of NO causes excessive vasodilatation. This hyperperfusion is manifested by hyperthermia of the overlying skin, while NO enhances nociception, aggravating orofacial pain. An alternative mechanism involving NO as a neurotransmitter at the CNS level may contribute to orofacial pain, but seems not to account for all the known clinical observations.

METHODS

Two groups of subjects were studied: 5 patients with COP and 59 control subjects. For each subject we collected blood samples for analysis of nitrite\nitrate (or NOx).

RESULTS

(1) NOx blood levels for 5 patients diagnosed with COP was 65.9 microM (SD of 10.4) verses 42.7 microM (SD of 24.2) for 59 control subjects, the difference being statistically significant, t-statistic = -2.12 (P > .05). (2) No statistical difference was found for NOx blood levels for 59 control subjects divided by gender (male vs female), with 23 female controls having NOx blood levels of 42.6 microM (SD of 25.2) and male controls having NOx blood levels of 42.8 microM (SD of 24.0), t-statistic = -0.03, P = .98.

CONCLUSION

This pilot study suggests that NO blood levels may have an association with COP. A better understanding of the mechanism of chronic orofacial pain is expected to lead to more precise diagnostic staging and management of this disorder.

Endogenous nitric oxide modulates responses of tissue and airway resistance to vagal stimulation in piglets

The role of endogenous nitric oxide (NO) in modulating the excitatory response of distal airways to vagal stimulation is unknown. In decerebrate, ventilated, open-chest piglets aged 3-10 days, lung resistance (RL) was partitioned into tissue resistance (Rti) and airway resistance (Raw) by using alveolar capsules. Changes in RL, Rti, and Raw were evaluated during vagal stimulation at increasing frequency before and after NO synthase blockade with N(omega)-nitro-L-arginine methyl ester (L-NAME). Vagal stimulation increased RL by elevating both Rti and Raw. NO synthase blockade significantly increased baseline Rti, but not Raw, and significantly augmented the effects of vagal stimulation on both Rti and Raw. Vagal stimulation also resulted in a significant increase in cGMP levels in lung tissue before, but not after, L-NAME infusion. In seven additional piglets after RL was elevated by histamine infusion in the presence of cholinergic blockade with atropine, vagal stimulation failed to elicit any change in RL, Rti, or Raw. Therefore, endogenous NO not only plays a role in modulating baseline Rti, but it opposes the excitatory cholinergic effects on both the tissue and airway components of RL. We speculate that activation of the NO/cGMP pathway during cholinergic stimulation plays an important role in modulating peripheral as well as central contractile elements in the developing lung.

Ionic mechanisms and Ca(2+) regulation in airway smooth muscle contraction: do the data contradict dogma?

In general, excitation-contraction coupling in muscle is dependent on membrane depolarization and hyperpolarization to regulate the opening of voltage-dependent Ca(2+) channels and, thereby, influence intracellular Ca(2+) concentration ([Ca(2+)](i)). Thus Ca(2+) channel blockers and K(+) channel openers are important tools in the arsenals against hypertension, stroke, and myocardial infarction, etc. Airway smooth muscle (ASM) also exhibits robust Ca(2+), K(+), and Cl(-) currents, and there are elaborate signaling pathways that regulate them. It is easy, then, to presume that these also play a central role in contraction/relaxation of ASM. However, several lines of evidence speak to the contrary. Also, too many researchers in the ASM field view the sarcoplasmic reticulum as being centrally located and displacing its contents uniformly throughout the cell, and they have focused almost exclusively on the initial single [Ca(2+)] spike evoked by excitatory agonists. Several recent studies have revealed complex spatial and temporal heterogeneity in [Ca(2+)](i), the significance of which is only just beginning to be appreciated. In this review, we will compare what is known about ion channels in ASM with what is believed to be their roles in ASM physiology. Also, we will examine some novel ionic mechanisms in the context of Ca(2+) handling and excitation-contraction coupling in ASM.

Nitric oxide-dependent modulation of smooth-muscle tone by airway parasympathetic nerves

We addressed the hypothesis that noncholinergic parasympathetic nerves modulate airway smooth-muscle (ASM) tone in guinea pigs. The NO synthase inhibitor L-N(G)-nitro-arginine (L-NNA) and the guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) potentiated cholinergic contractions and partly inhibited noncholinergic relaxations of the trachealis evoked by nerve stimulation in vitro or in situ. When delivered selectively to the trachea in situ, L-NNA and ODQ also increased baseline cholinergic tone of the trachealis, and L-NNA potentiated histamine-induced contractions of the trachealis in situ. L-Arginine prevented the effects of L-NNA. Vagotomy or selective nerve blockade with tetrodotoxin (TTX) mimicked the effects of L-NNA on histamine responses. The effects of TTX and L-NNA were not additive, however, suggesting that the two agents have common mechanisms of action, and indicating that other nonadrenergic, noncholinergic relaxant neurotransmitters lack influence under baseline conditions. When reflexly activated by bradykinin, noncholinergic parasympathetic nerves partly reversed histamine-induced contractions of the trachealis. L-NNA failed to inhibit this response, however, and did not potentiate the reflex tracheal cholinergic contractions produced by bradykinin. These results show that noncholinergic parasympathetic nerves modulate ASM tone. The NO-dependent component of this response is most effective at baseline levels of nerve activity.

Differential distribution of ionic channels and muscarinic receptors at the cat tracheal neuromuscular junction

The ionic and pharmacological properties of atropine-sensitive excitatory junction potentials (EJPs) were investigated by the double sucrose gap and microelectrode membrane potential recording methods, and compared with those of inward currents evoked by carbachol (I(CCh)), in cat tracheal smooth muscle. A single and repetitive field stimulation (10-30 V, 50 micros, 20 Hz) evoked atropine-inhibitable EJPs and associated twitch-like contractions. Reduction in external Na+ concentration strongly, but in the external Cl- concentration, decreased the EJP amplitude after 5 min superfusion, although prolonged exposure to low Cl- solutions attenuated the EJPs modestly. Chloride channel blockers such as 9-AC and niflumic acid (each 100 microM), at concentrations high enough to inhibit I(CCh) almost completely, failed to abolish the EJPs. Pirenzepine, AF-DX116 and 4-DAMP all effectively inhibited the EJPs at their concentrations to block respective muscarinic receptor subtypes relatively specifically, while depletion of internal stores by 10 mM caffeine and/or 3 microM ryanodine caused only a partial decrease in the EJP amplitude. These properties are considerably different from those of I(CCh) which is activated exclusively through activation of the M3 receptor/IP3-mediated Ca2+ release pathway and reflects mostly a Ca2+-dependent Cl- current, and suggests the differential distribution of muscarinic receptors and ionic channels inside and outside of the cholinergic neuromuscular junction of this muscle.

Pituitary adenylate cyclase activating peptide mediates inhibitory nonadrenergic noncholinergic relaxation

We investigated the contribution of pituitary adenylate cyclase activating peptide (PACAP) to inhibitory nonadrenergic noncholinergic (inhibitory-NANC) relaxation of tracheal smooth muscle in cats. We also investigated the roles of vasoactive intestinal peptide (VIP) and nitric oxide (NO) on this function. Smooth muscle strips prepared from feline trachea were precontracted with 1 microM serotonin, and inhibitory-NANC relaxation was induced by electrical-field stimulation in the presence of atropine and propranolol. PACAP-(6-38) (a selective antagonist of PACAP; 1, 3 and 10 microM), VIP-(10-28) (a selective antagonist of VIP; 1, 3 and 10 microM) and N(omega)-nitro-L-arginine methyl ester (L-NAME, a selective NO synthase inhibitor; 3, 10 and 30 microM) each partially but significantly attenuated the amplitude of inhibitory-NANC relaxation. The effects of PACAP-(6-38) and VIP-(10-28) were additive. Addition of PACAP-(6-38) and/or VIP-(10-28) further attenuated relaxation in the presence of L-NAME. These results suggest that PACAP, VIP and NO contribute to the relaxation induced by inhibitory-NANC in tracheal smooth muscle in cats, and that they mediate this relaxation via different pathways.

Effects of superoxide generating systems on muscle tone, cholinergic and NANC responses in cat airway

To study the possible role of reactive oxygen species in airway hyperreactivity, we examined the effects of the superoxide anion radical (O(2)(-)) generating systems, pyrogallol and xanthine with xanthine oxidase, on muscle tone, excitatory and inhibitory neurotransmission in the cat airway. Smooth muscle contraction or non-adrenergic non-cholinergic (NANC) relaxation evoked by electrical field stimulation (EFS) were measured before or after O(2)(-) generating systems with or without diethydithiocarbamic acid (DEDTCA), an inhibitor of endogenous superoxide dismutase (SOD). Resting membrane potential or excitatory junction potential (EJP) were also measured in vitro. Both pyrogallol and xanthine/xanthine oxidase produced biphasic changes in basal and elevated (by 5-HT) muscle tone. After SOD pretreatment, both systems consistently produced a prolonged contraction, thereby indicating that O(2)(-) was converted to H(2)O(2) by the action of SOD and as a result the actions of O(2)(-) were lost but those of H(2)O(2) introduced. The O(2)(-) showed no significant effect on smooth muscle contraction or EJP evoked by EFS, however after DEDTCA pretreatment, it evoked initial enhancement followed by suppression of the contraction and EJP. DEDTCA pretreatment ameliorated the inhibitory action of pyrogallol and xanthine/xanthine oxidase on the NANC relaxation, probably because O(2)(-) could combine with endogenous NO to form peroxynitrite. These results indicate that the O(2)(-) generating systems have multiple actions, presumably due to the presence and simultaneous action of at least two different reactive oxygen species (O(2)(-) and H(2)O(2)). While H(2)O(2) seems to be responsible for elevation of muscle tone and augmentation of smooth muscle contraction by EFS, O(2)(-) inhibits muscle tone, cholinergic and NANC neurotransmission.

The prostaglandin E series modulates high-voltage-activated calcium channels probably through the EP3 receptor in rat paratracheal ganglia

The modulation of high-voltage-activated (HVA) Ca2+ channels by the prostaglandin E series (PGE1 and PGE2) was studied in the paratracheal ganglion cells. Prostaglandin E1, E2, STA2 (a stable analogue of thromboxane A2), 17-phenyl-trinor-PGE2 (an EP1-selective agonist) and sulprostone (an EP3-selective agonist) inhibited the HVA Ca2+ current (HVA ICa) dose-dependently, and the rank order of potency to inhibit HVA Ca2+ channels was sulprostone>PGE2, PGE1>STA2>>17-phenyl-trinor-PGE2. SC-51089 (10(-5) M), a selective EP1-receptor antagonist, showed no effect on the PGE1- or PGE2-induced inhibition of the HVA ICa, thereby indicating that PGE1- and PGE2-induced inhibition of the HVA Ca2+ channels is possibly mediated by the EP3 receptor. The PGE1-sensitive component of the current was markedly reduced in the presence of omega-conotoxin-GVIA (3x10(-6) M), but not with nifedipine (3x10(-6) M). PGE1 and PGE2 also inhibited the remaining ICa in a saturating concentration of nifedipine, omega-conotoxin-GVIA and omega-conotoxin-MVIIC, suggesting that R-type Ca2+ channels are involved. The inhibitory effect of PGE1 or sulprostone was prevented by pretreatment with pertussis toxin [islet activating protein (IAP)] or phorbol-12-myristate-13-acetate (PMA), and the protein kinase C (PKC) inhibitor chelerythrine blocked the action of PMA. It was concluded that PGE1 selectively reduces both N- and R-type Ca2+ currents by activating a G-protein probably through the EP3 receptor in paratracheal ganglion cells.

Multiple calcium channels regulate neurotransmitter release from vagus nerve terminals in the cat bronchiole

1. Twitch-like contractions and non-adrenergic non-cholinergic (NANC) relaxations evoked by electrical field stimulation (EFS) of the cat bronchiole were used to examine the voltage-activated calcium channels involved in excitatory and inhibitory neurotransmission in the cat bronchiole. 2. Nifedipine (50 microM), the L-type calcium channel antagonist, did not affect the twitch-like contraction and NANC relaxations. However, low concentrations of the N-type calcium channel blocker omega-conotoxin GVIA (omega-CgTX GVIA) (0.1 microM) irreversibly abolished twitch-like contractions evoked by trains of EFS </=10 stimuli at 20 Hz. 3. After the prolonged treatment with 0.1 microM omega-CgTX GVIA, EFS evoked initial fast and later slow NANC relaxations in the presence of 5-HT (10 microM), atropine and guanethidine (1 microM each). However increased concentration of omega-CgTX GVIA (1 microM) completely suppressed the slow NANC relaxation without affecting the initial fast component. 4. omega-agatoxin IVA (100 nM), the P- and Q-type calcium channel inhibitor, and nimodipine (10 microM), the L- and T-type calcium channel blocker, did not affect the amplitude of the initial fast NANC relaxation in the absence or presence of omega-CgTX GVIA (1 microM). 5. The contraction or relaxation induced by exogenous acetylcholine (ACh) (0.5 microM) or the nitric oxide donor, s-nitroso-N-acetyl penicillamine (SNAP) (1 microM) were not affected by omega-CgTX GVIA (1 microM). 6. Taken together, these results suggest that generation of twitch-like contraction and later slow NANC relaxation are regulated by N-type calcium channels, whereas generation of the initial fast NANC relaxation possibly involves R-type calcium channel.

The possible effect of nitric oxide on relaxation and noradrenaline release in the isolated rabbit urethra

We evaluated the effects of N(omega)-nitro-L-arginine (L-NNA, a nitric oxide (NO) synthase inhibitor) and carboxy-2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (carboxy-PTIO, a NO scavenger) on NO-mediated relaxation and noradrenaline release from adrenergic nerve endings induced by electrical field stimulation in the rabbit urethra. Electrical field stimulation caused frequency-dependent relaxation of rabbit urethral smooth muscles precontracted with phenylephrine. The relaxation responses were significantly inhibited by treatment with L-NNA or carboxy-PTIO. The inhibitory effect of carboxy-PTIO was significantly weaker than that of L-NNA. Electrical field stimulation caused significant noradrenaline release from adrenergic nerve endings in the rabbit urethra. Treatment with carboxy PTIO enhanced electrical field stimulation-induced noradrenaline release, and simultaneous application of L-NNA and carboxy-PTIO did not further enhance noradrenaline release in the rabbit urethra. As carboxy-PTIO reacts only with the free radical NO, the present results suggest that free radical NO and NO-containing compounds are involved in the L-NNA-sensitive nitrergic nerve-mediated relaxation in the rabbit urethra. At the same time free radical NO has a prejunctional action by which it may inhibit noradrenaline release from adrenergic nerves.

Cyclic GMP-dependent but G-kinase-independent inhibition of Ca2+-dependent Cl- currents by NO donors in cat tracheal smooth muscle

1. The effects of NO donors on Ca2+-dependent Cl- currents (ICl(Ca)) were investigated in freshly isolated cat tracheal myocytes using the whole-cell patch clamp technique. 2. With nystatin-perforated whole-cell recording, carbachol (CCh, >/= 1 microM) induced a transient inward current (ICCh) with a reversal potential of about -20 mV. Activation of ICCh probably occurred through the M3 muscarinic receptor, since nanomolar concentrations of 4-diphenylacetoxy-N-methylpiperidine methobromide (4-DAMP) greatly inhibited this current, while 11-(2-(diethylamino)methyl)-1-piperidinylacetyl)-5, 11-dihydro-6H-pyrido (2,3beta) (1,4)benzodiazepine-6-one (AF-DX 116) or pirenzepine at concentrations of up to 1 microM were almost ineffective. 3. Chloride channel/transporter blockers such as DIDS (100 microM), anthracene-9-carboxylic acid (9-AC, 100 microM) and niflumic acid (100 microM) greatly inhibited ICCh, but cation channel blockers, such as nifedipine (10 microM), Zn2+ (500 microM) or Gd3+ (500 microM), were without effect. 4. Activation of ICCh was strongly attenuated by pretreatment with ryanodine (4 microM) plus caffeine (10 mM). Addition of neomycin (1 mM) into the bath or inclusion of heparin (3 mg ml-1) in the pipette abolished a substantial part of ICCh. These results suggest that ICCh is ICl(Ca), which is activated by inositol 1,4,5-trisphosphate (IP3)-mediated Ca2+ release. 5. The nitric oxide donor S-nitroso-N-acetyl penicillamine (SNAP) reduced the amplitude of ICCh dose dependently (IC50, approximately 10 microM). Similar inhibition was also exerted by other types of NO donor such as glyceryl trinitrate (GTN) and (+/-)-E-methyl-2-(E-hydroxyimitol)-5-nitro-6-methoxy-3- hexeneamide (NO-R). 6. SNAP-induced ICCh inhibition was effectively antagonized by Methylene Blue (1-100 nM), and mimicked by dibutyryl cGMP (db-cGMP) (0.5-1 mM), whereas two structurally distinct types of cGMP-dependent (G)-kinase inhibitor, N-(2-aminoethyl)-5-isoquinilinesulphonamide (H-8, 2.5 microM) and KT5823 (1 microM), failed to counteract the inhibitory effects of SNAP or db-cGMP. Another G-kinase-specific inhibitor Rp-8-(para-chlorophenylthio)guanosine-3',5'-cyclic monophosphorothioate (Rp-8-pCPT-cGMPS; 1 microM) itself caused a marked reduction in ICCh. 7. SNAP (100 microM) or db-cGMP (100 microM) exhibited no inhibitory actions, when caffeine (10 mM) or photolytically released IP3 were used instead of CCh to activate the inward current. 8. These results suggest that inhibition of ICCh by NO donors involves a cGMP-dependent but G-kinase-independent mechanism, which may operate at a site(s) between the muscarinic (M3) and IP3 receptors.

The possible role of nitric oxide in the physiopathology of pain associated with temporomandibular joint disorders

Temporomandibular joint disorders (TMD) pose a significant challenge to the practice of oral and maxillofacial surgery. When painful, TMD are generally associated with hyperthermia of the overlying skin. It is hypothesized that this skin hyperthermia, caused by regional vasodilation, is induced by nitric oxide (NO) produced in the extravascular space of the joint. Extravascular NO can be produced by osteoblasts, chondrocytes and macrophages, or by stimulated neurons. It is suggested that this kind of pain is associated with NO-enhanced sensitivity of the peripheral nociceptors. Verification and clinical implications of the proposed mechanism are discussed.

Physiological features of visceral smooth muscle cells, with special reference to receptors and ion channels

Visceral smooth muscle cells (VSMC) play an essential role, through changes in their contraction-relaxation cycle, in the maintenance of homeostasis in biological systems. The features of these cells differ markedly by tissue and by species; moreover, there are often regional differences within a given tissue. The biophysical features used to investigate ion channels in VSMC have progressed from the original extracellular recording methods (large electrode, single or double sucrose gap methods), to the intracellular (microelectrode) recording method, and then to methods for recording from membrane fractions (patch-clamp, including cell-attached patch-clamp, methods). Remarkable advances are now being made thanks to the application of these more modern biophysical procedures and to the development of techniques in molecular biology. Even so, we still have much to learn about the physiological features of these channels and about their contribution to the activity of both cell and tissue. In this review, we take a detailed look at ion channels in VSMC and at receptor-operated ion channels in particular; we look at their interaction with the contraction-relaxation cycle in individual VSMC and especially at the way in which their activity is related to Ca2+ movements and Ca2+ homeostasis in the cell. In sections II and III, we discuss research findings mainly derived from the use of the microelectrode, although we also introduce work done using the patch-clamp procedure. These sections cover work on the electrical activity of VSMC membranes (sect. II) and on neuromuscular transmission (sect. III). In sections IV and V, we discuss work done, using the patch-clamp procedure, on individual ion channels (Na+, Ca2+, K+, and Cl-; sect. IV) and on various types of receptor-operated ion channels (with or without coupled GTP-binding proteins and voltage dependent and independent; sect. V). In sect. VI, we look at work done on the role of Ca2+ in VSMC using the patch-clamp procedure, biochemical procedures, measurements of Ca2+ transients, and Ca2+ sensitivity of contractile proteins of VSMC. We discuss the way in which Ca2+ mobilization occurs after membrane activation (Ca2+ influx and efflux through the surface membrane, Ca2+ release from and uptake into the sarcoplasmic reticulum, and dynamic changes in Ca2+ within the cytosol). In this article, we make only limited reference to vascular smooth muscle research, since we reviewed the features of ion channels in vascular tissues only recently.

Acetylcholine modulation of high-voltage-activated calcium channels in the neurones acutely dissociated from rat paratracheal ganglia

1. The modulation of high-voltage-activated (HVA) Ca2+ channels by acetylcholine (ACh) was studied in the paratracheal ganglion cells acutely dissociated from 2-week-old Wistar rats by use of the nystatin perforated patch recording configuration under voltage-clamp conditions. 2. ACh inhibited the HVA Ca2+ currents in a concentration- and voltage-dependent manner. 3. The inhibition was mimicked by a muscarinic agonist, oxotremorine. Pirenzepine and methoctramine produced parallel shifts to the right in the ACh concentration-response curves. Schild analysis of the ACh concentration-ratios yield pA2 values for pirenzepine and methoctramine of 6.85 and 8.57, respectively, suggesting the involvement of an M2 receptor. 4. Nifedipine, omega-conotoxin-GVIA and omega-conotoxin-MVIIC reduced the HVA I(Ca) by 16.8, 59.2 and 6.3%, respectively. A current insensitive to all of these Ca2+ antagonists, namely 'R-type', was also observed. The results indicated the existence of L-, N-, P/Q-, and R-type Ca2+ channels. 5. The ACh-sensitive current component was markedly reduced in the presence of omega-conotoxin-GVIA, but not with both nifedipine and omega-conotoxin-MVIIC. ACh also inhibited the R-type HVA I(Ca) remaining in saturating concentrations of nifedipine, omega-conotoxin-GVIA and omega-conotoxin-MVIIC. 6. The inhibitory effect of ACh was prevented by pretreatment with pertussis toxin. 7. It was concluded that ACh selectively reduces both the N- and R-type Ca2+ channels, by activating pertussis toxin sensitive G-protein through the M2 muscarinic receptor in paratracheal ganglion cells.

Myogenic nitric oxide synthase activity in canine lower oesophageal sphincter: morphological and functional evidence

1. Studies on canine lower oesophageal sphincter (LOS) evaluated the existence and function of a myogenic, nitric oxide synthase (NOS) by use of immunocytochemistry for NOS isozymes, NADPH-d histochemistry, [3H]-L-arginine to [3H]-L-citrulline transformation. In addition, functional studies in the muscle bath were performed. 2. Smooth muscle bundles or freshly isolated smooth muscle cells of LOS were NADPH-d reactive but did not recognize some antibodies against neural, endothelial or inducible NOS. NADPH-d reactivity and immunoreactivity to a neural NOS antibody were colocalized in LOS enteric nerves. Muscle plasma membrane-enriched fractions from fresh and cultured LOS cells converted [3H]-L-arginine to [3H]-L-citrulline; activity was mostly Ca2+/calmodulin-dependent. 3. N-Nitro-L-arginine (L-NOARG) persistently increased tone (blocked by L-arginine) in muscle strips despite blockade of nerve function. Nifedipine prevented or abolished L-NOARG-induced, but not carbachol-induced, contraction showing that tone increase by L-NOARG required functional L-Ca channels. 4. Membrane-bound, myogenic NOS in canine LOS may release NO continuously when Ca2+ entry through L-Ca channels occurs under physiological conditions and thereby modulate tone in LOS.

Mediators and mechanisms of relaxation in rabbit urethral smooth muscle

1. Electrophysiological and mechanical experiments were performed to investigate whether the nitric oxide (NO)-mediated relaxation of rabbit urethral smooth muscle is associated with a hyperpolarization of the membrane potential. In addition, a possible role for vasoactive intestinal peptide (VIP) and carbon monoxide (CO) as relaxant agents in rabbit urethra was investigated. 2. Immunohistochemical experiments were performed to characterize the NO-synthase (NOS) and VIP innervation. Possible target cells for NO were studied by using antisera against cyclic GMP. The cyclic GMP-immunoreactivity was investigated on tissues pretreated with 1 mM IBMX, 0.1 mM zaprinast and 1 mM sodium nitroprusside. 3. Intracellular recordings of the membrane potential in the circular smooth muscle layer revealed two types of spontaneous depolarizations, slow waves with a duration of 3-4 s and an amplitude of 30-40 mV, and faster (0.5-1 s), more irregular depolarizations with an amplitude of 5-15 mV. The resting membrane potential was 39 +/- 1 mV (n = 12). Application of NO (30 microM), CO (30 microM) or VIP (1 microM) did not change the resting membrane potential. 4. Both NO (1-100 microM) and VIP (1 nM-1 microM) produced concentration-dependent relaxations amounting to 87 +/- 4% and 97 +/- 2% (n = 6), respectively. The relaxant effect of CO (1-30 microM) amounted to 27 +/- 4% (n = 5) at the highest concentration used. 5. Immunohistochemical experiments revealed a rich supply of NOS-immunoreactive nerve fibres in the smooth muscle layers. Numerous spinous cyclic GMP-immunoreactive cells were found interspersed between the smooth muscle bundles, mainly localized in the outer layer. These cells had long processes forming a network surrounding the smooth muscle bundles. VIP-immunoreactivity was sparse in comparison to NOS-immunoreactive nerves. 6. The rich supply of NOS-immunoreactive nerve fibres supports the view that NO is an important NANC-mediator in the rabbit urethra. In contrast to several other tissues, the relaxant effect of NO in the rabbit urethra does not seem to be mediated by hyperpolarization. The network of cyclic GMP-immunoreactive cells may constitute target cells for NO, but their function remains to be established.

Possible role of cAMP, cGMP and [Ca2+]i during NANC relaxation in the cat airway smooth muscle

To investigate the possible role of cyclic nucleotides and [Ca2+]i in non-adrenergic non-cholinergic (NANC) relaxations evoked by electrical field stimulation (EFS) in the cat airway, we studied the effects of specific phosphodiesterase (PDE) type IV or V inhibitors on the biphasic-NANC relaxations, the correlation between NANC relaxation and changes in intracellular levels of cAMP and cGMP ([cAMP]i and [cGMP]i), and measured changes in [Ca2+]i during the NANC relaxation. EFS (repetitive stimuli at 20 Hz, 1 or 4 ms pulse duration, 50 V) applied to the bronchial smooth muscle during contraction induced by 5-HT (10(-5) M) in the presence of atropine (10(-6) M) and guanethidine (10(-6) M) elicited biphasic NANC relaxations. Zaprinast (> 3 x 10(-7) M), a specific PDE type V inhibitor, preferentially enhanced the amplitude of the first component of the NANC relaxations. However, rolipram (> 3 x 10(-7) M) enhanced both the first and second component of the NANC relaxation to a similar extent. In the trachea, EFS evoked monophasic NANC relaxation accompanied by a concomitant accumulation of [cAMP]i and [cGMP]i. Pretreatment with rolipram (3 x 10(-6) M) enhanced the accumulation of [cAMP]i and amplitude of NANC relaxation evoked by EFS. However, zaprinast did not affect the amplitude of NANC relaxation although it significantly increased the levels of [cGMP]i. Nomega-Nitro-L-arginine methylester (L-NAME; 10(-5) M) completely suppressed the accumulation of [cGMP]i but only partly suppressed the NANC relaxation evoked by EFS. In contrast, EFS significantly enhanced [cAMP]i in the presence of L-NAME. During NANC relaxation, time-dependent decrease in [Ca2+]i occurred, which was partly suppressed by L-NAME. These results indicate that NANC relaxation is associated with concomitant accumulation in both [cAMP]i and [cGMP]i, and decrease in [Ca2+]i. However, the timing of the action of [cGMP]i and [cAMP]i in NANC relaxations differs in the central and peripheral airway.

Nitric oxide and the non-adrenergic non-cholinergic neurotransmission

In the early 1960s, the first evidence was reported demonstrating neurally mediated responses in the presence of adrenergic and cholinergic antagonists, leading to the introduction of the concept of non-adrenergic non-cholinergic neurotransmission. The inhibitory component of this part of the autonomic nervous system has been illustrated in numerous organ systems mediating a wide range of physiological events. Since the discovery of these nerves, several substances have been proposed as putative neurotransmitter, with ATP and vasoactive intestinal polypeptide as main candidates. Finally, the ongoing research on the nature of the substance released by these nerves has generated the nitrergic theory proposing nitric oxide as putative neurotransmitter. By now, increasing evidence is reported to support the idea that inhibitory neurons release more neurotransmitters, interacting with each other at pre- and/or postsynaptic levels.

Role of nitric oxide in the physiopathology of pain

Many painful disorders, including joint dysfunctions such as rheumatoid arthritis (RA) or temporomandibular joint disorders (TMD), are associated with hyperthermia of the overlying skin. The same is true of certain intractable chronic pain conditions, such as chronic orofacial pain, which may be associated with TMD. We suggest that this skin hyperthermia, caused by regional vasodilation, is induced by extravascular nitric oxide (NO). Extravascular NO can be produced in the affected joint by osteoblasts, chondrocytes, and macrophages, by mechanical stimulation of endothelial cells, or by stimulated neurons. In view of a strong correlation between pain and skin hyperthermia in these disorders, and the evidence that NO enhances the sensitivity of peripheral nociceptors, we also suggest that at least this kind of pain is associated with excessive local level of NO. This hypothesis can be verified by dynamic area telethermometry, assessing the effect of NO on the sympathetic nervous function. This mechanism, which is in line with the general role of NO as a mediator between different organ systems, also may be relevant to any pain associated with enhanced immune response. Clinical implications of the proposed mechanism are discussed.

Contribution of type I NOS to expired gas NO and bronchial responsiveness in mice

Nitric oxide (NO) can be measured in the expired gas of humans and animals, but the source of expired NO (F(E)NO) and the functional contribution of the various known isoforms of NO synthase (NOS) to the NO measured in the expired air is not known. F(E)NO was measured in the expired air of mice during mechanical ventilation via a tracheal cannula. F(E)NO was significantly higher in wild-type B6SV129J +/+ mice than in mice with a targeted deletion of type I (neural) NOS (nNOS, -/-) (6.3 +/- 0.9 vs. 3.9 +/- 0.4 parts/billion, P = 0.0345, for +/+ and -/- mice, respectively), indicating that approximately 40% of the NO in expired air in B6SV129 mice is derived from nNOS. Airway responsiveness to methacholine (MCh), assessed by the log of the effective dose of MCh for a doubling of pulmonary resistance from baseline (ED(200)R(L)), was significantly lower in the -/- nNOS mice than in the wild-type mice (logED(200)R(L), 2.24 +/- 0.07 vs. 2.51 +/- 0.06 microg/kg, respectively; P = 0.003). These findings indicate that nNOS significantly contributes to baseline F(E)NO and promotes airway hyperresponsiveness in the mouse.

Hydrogen peroxide induced responses of cat tracheal smooth muscle cells

1. The effects of hydrogen peroxide (H2O2) (10(-6)-10(-3) M) on membrane potential, membrane currents, intracellular calcium concentration, resting muscle tone and contractions elicited by electrical field stimulation (EFS) and carbachol were examined in cat tracheal strips and isolated smooth muscle cells. 2. H2O2 (10(-4) and 10(-5) M) enhanced the amplitude of contractions and excitatory junction potentials (e.j.p.) evoked by EFS without changing muscle tone and resting membrane potential of the tracheal smooth muscle, and enhanced the contraction induced by carbachol (10(-3) M). At an increased concentration (10(-3) M), H2O2 elevated resting muscle tone and marginally hyperpolarized the membrane in the majority of the cells. 3. In 51 out of 56 cells examined, H2O2 (10(-6)-10(-3) M) elicited an outward current at a holding potential of -40 mV and enhanced the frequency of the spontaneous transient outward current (STOC). In 20 cells the outward current was preceded by a small inward current. In the other cells, H2O2 elicited only an inward current or did not affect the background current. 4. In Ca2+ free solution the action of H2O2 on the resting muscle tone, STOCs, background current and on the current induced by ramp depolarization was significantly reduced. 5. H2O2 (10(-4) M) increased the intracellular ionized calcium concentration both in the absence and presence of external Ca2+. However, the effect developed faster and was of a higher amplitude in the presence of external Ca2+. 6. These results suggest that H2O2 increases intracellular Ca2+, with a subsequent augmentation of stimulation-evoked contractions, and enhances Ca2+ and voltage-sensitive potassium conductance.

Pharmacological properties of non-adrenergic, non-cholinergic inhibitory transmission in chicken gizzard

1. Non-adrenergic, non-cholinergic (NANC) inhibitory transmission in chicken gizzard was studied by use of intracellular microelectrode techniques. Changes in membrane potential in response to NANC nerve stimulation were recorded in the gizzard smooth muscle pretreated with atropine (1 microM) and guanethidine (1 microM). 2. Field stimulation of the intramural nerves (FS) evoked inhibitory junction potentials (i.j.ps) which were abolished by tetrodotoxin (1 microM), but not inhibited at all by K+ channel blockers including apamin (0.5 microM), tetraethylammonium (TEA, 10 mM), charybdotoxin (0.2 microM) and glibenclamide (10 microM). 3. NG-nitro-L-arginine (3 mM), an inhibitor of nitric oxide (NO) synthase, inhibited i.j.ps. The effect was reversed by L-arginine (3 mM), but not by D-arginine (3 mM). 4. 8-Bromo cyclic GMP (100 microM), a membrane permeable analogue of cyclic GMP, produced a membrane hyperpolarization which was blocked by TEA (10 mM) or glibenclamide (10 microM). 5. NO at concentrations of up to 400 microM affected neither i.j.ps nor resting membrane potential. On the other hand, NO (80 microM) caused the membrane to hyperpolarize in the smooth muscle of guinea-pig ileum. 6. These results suggest that in the chicken gizzard, NANC i.j.ps may not arise from opening of conventional types of K+ channel and that NO seems unlikely to be involved in the generation of i.j.ps. A possible mechanism by which the inhibitory effect of NG-nitro-L-arginine on i.j.ps was brought about will be discussed.

NANC neural control of airway smooth muscle tone

1. This review addresses the functional role of the nonadrenergic, noncholinergic (NANC) neural response in the control of airway smooth muscle tone. 2. Functional data from guinea pig airways in vitro indicate that the level of basal smooth muscle tone determines the direction and magnitude of the NANC neural response such that it can stabilise tone. 3. The NANC stabilising effect on tone is adjustable through variation in impulse frequency and the NANC stabilising effect is also powerful; it can abolish near-maximum differences in tone. 4. Cholinergic activation increases the level towards which the NANC responses tend to adjust tone. 5. Adrenergic activation reduces the level towards which the NANC responses tend to adjust tone via beta-adrenoceptors. 6. NANC neural activation, with or without simultaneous adrenergic or cholinergic activation, can stabilise tone at low, intermediate or high levels with a high degree of accuracy. 7. Evidence from other investigators on effects of putative NANC neurotransmitters supports the idea of functional interactions within the NANC system in the airways. 8. It remains to be confirmed whether or not NANC responses play a stabilising role in the control of airway smooth muscle tone in vivo and in higher mammals.

The possible role of nitric oxide in relaxations and excitatory neuroeffector transmission in the cat airway

1. To study the possible role of nitric oxide (NO free radical; NO) or NO-containing compounds in the non-adrenergic, non-cholinergic (NANC) relaxations, we observed the effects of carboxy-2-phenyl-4, 4, 5, 5-tetramethyl-imidazoline-1-oxyl-3-oxide (C-PTIO; a newly synthesized NO scavenger) on NANC relaxations in the cat airway. In addition, we also observed the effects of C-PTIO on excitatory junction potentials (EJPs), since NO has a prejunctional action on transmitter release. 2. Nitrosocystine (Cys-NO) (10(-7)-10(-3) M) dose-dependently relaxed the bronchial tissue in the presence of 5-HT, atropine and guanethidine and C-PTIO (10(-4) M) shifted the concentration-response curve of the Cys-NO to the right. 3. Electrical field stimulation (EFS) evoked biphasic NANC relaxations in the small bronchi of the cat. In general, C-PTIO suppressed non-selectively both the first and second components of the NANC relaxations to a similar extent. However, in some bronchial preparations C-PTIO (10(-4) M) selectively suppressed the first component of the NANC relaxation to approximately 50% of the initial value, enhancing the amplitude of the second component of the NANC relaxations. 4. After pretreatment of the bronchial tissues with alpha-chymotrypsin (1 unit ml-1) for 30 min in order to inhibit any response to peptides, EFS evoked monophasic NANC relaxation. C-PTIO (10(-5) - 10(-4) M) dose-dependently suppressed, and at a concentration of 10(-4) M almost halved, the amplitude of NANC relaxation. Additional application of L-NAME further reduced the C-PTIO-resistant NANC relaxation to 20-30% of the initial value. 5. C-PTIO (10(-4) M) enhanced the EJP amplitude evoked by single EFS in the trachea but not in the bronchi. However, C-PTIO enhanced the summation of the EJPs to repeated stimulation to a similar extent in the tracheal and bronchial tissues. Simultaneous application of C-PTIO and L-NAME did not further enhance the summation. 6. These results indicate that NO. and NO-containing compounds are involved in the L-NAME-sensitive NANC relaxation in the cat airway, and that only NO. has a prejunctional action which inhibits excitatory neuroeffector transmission.

Regional difference in the distribution of L-NAME-sensitive and -insensitive NANC relaxations in cat airway

1. To investigate the distribution profile of functional inhibitory non-adrenergic non-cholinergic (i-NANC) nerves and the contribution of NO to the NANC relaxation in the cat, we studied the effects of N omega-nitro-L-arginine methyl ester (L-NAME) on NANC relaxation elicited by electrical field stimulation (EFS) in the trachea, bronchus and bronchiole. 2. EFS applied to the tracheal smooth muscle during contraction induced by 5-HT (10(-5) M) in the presence of atropine (10(-6) M) and guanethidine (10(-6) M) elicited a monophasic NANC relaxation. By contrast, NANC relaxation elicited in the peripheral airway was biphasic, comprising an initial fast followed by a second slow component and L-NAME (10(-5) M) selectively abolished the first component without affecting the second one. In the trachea, L-NAME (10(-5) M) completely suppressed the monophasic NANC relaxation when single or short repetitive stimuli (< 5) with 1 ms pulse duration were applied. However, at higher repetitive stimuli (> 10) with 1 or 4 ms pulse duration, suppression of NANC relaxation was incomplete. 3. In the small bronchi obtained from L-NAME-pretreated cats, EFS applied during contraction induced by 5-HT (10(-5) M) elicited only the slow component of NANC relaxation which is sensitive to tetrodotoxin. 4. In the peripheral airway, a newly synthesized VIP antagonist (10(-6) M) or alpha-chymotrypsin (1 U ml-1) considerably attenuated the amplitude of L-NAME-insensitive relaxation. 5. Single or repetitive EFS consistently evoked excitatory junction potentials (EJPs) in the central and peripheral airways. When tissues were exposed to atropine (10(-6) M) and guanethidine (10(-6) M), single or repetitive EFS did not alter the resting membrane potential. 6. These results indicate that at least two neurotransmitters, possibly NO or NO-containing compounds and VIP, are involved in i-NANC neurotransmission and the distribution profile of the two components differs in the central and peripheral airway of the cat.