In Vitro Evaluation of Carbachol and Endothelin on Contractility of Colonic Smooth Muscle in Hirschsprung’s Disease

BACKGROUND

The hypomotility of colon observed in Hirschsprung’s disease (HD) has been attributed to congenital aganglionosis only. So far, it is not clear whether the contractility of colonic smooth muscle in this condition is altered or not. Therefore, the present study attempted to understand the contractile status of colonic segments of HD patients by examining carbachol and endothelin (ET-1) evoked colonic smooth muscle contractions in vitro .

METHODS

Contractile responses were recorded from strips of colonic segments obtained from HD patients, using organ bath preparations. Cholinergic agonist carbachol and ET-1 along with their antagonists were used to evoke contractile responses. Thereafter, the samples were histopathologically confirmed for HD.

RESULTS

Colonic strips of HD did not show any spontaneous contractions but responded to carbachol and ET-1 to a lesser extent. In HD, response of carbachol was blocked by atropine and hexamethonium by nearly 73% and 50% respectively. ET-1 induced contractile responses were blocked by ET-A and ET-B antagonist up to 40%, signifying the possible role of ET-A and ET-B receptors in HD colon contractility.

CONCLUSION

As evidenced by lack of spontaneous contractions and impaired carbachol and ET-1-induced contractile responses, it is concluded that, in addition to aganglionosis, decreased contractility of colonic smooth muscle may contribute to hypomotility observed in patients with HD.

Effects of the aqueous extract of Pittosporum mannii Hook. f. (Pittosporaceae) stem barks on spontaneous and spasmogen-induced contractile activity of isolated rat duodenum

ETHNOPHARMACOLOGICAL RELEVANCE

Pittosporum mannii Hook. f. (Pittosporaceae) is a plant widely used in traditional medicine in Cameroon for the treatment of many gastrointestinal disorders including diarrhea. To date, no pharmacological study on the antidiarrheal and the antispasmodic properties of this plant has been reported. The aim of the present study was to evaluate in vitro the relaxant activity of the aqueous extract of stem barks of P. mannii (PMAE) on rat duodenum.

MATERIALS AND METHODS

Different concentrations of PMAE were tested separately (10-80 µg/mL) or cumulatively (5-80 µg/mL) on spontaneous and spasmogen (carbachol, histamine and KCl)-induced contractions of isolated rat duodenum strips.

RESULTS

At concentrations ranging from 10 to 80 µg/mL, PMAE significantly decreased the tonus and the amplitude of spontaneous contractions. However, at high concentration (80 µg/mL), the extract elicited a transient relaxation was followed by a slight increase of tonus, while the amplitude remained lower compared to the normal spontaneous activity. The relaxant effect of the extract was not significantly affected in the presence of atropine (0.713 µg/mL) and promethazine (0.5 µg/mL). In addition, PMAE (20, 40, and 80 µg/mL) partially but significantly inhibited in a concentration related manner the contractions induced by carbachol (10(-9)-10(-4)M) and histamine (10(-9)-10(-4)M) on rat duodenum. PMAE (10-80 µg/mL) also significantly induced a concentration-dependent relaxation on KCl (20mM, 50mM, 10(-3)-6.10(-3)M)-induced contraction of rat duodenum.

CONCLUSIONS

These results show that the aqueous extract of P. mannii stem barks possesses antispasmodic and spasmolytic effects at lower concentrations; therefore, supporting the use of the stem barks of this plant in the folk medicine for the treatment of diarrhea. However, caution should be paid while using higher concentrations that instead might produce spasmogenic effect and might worsen the diarrheal condition. The relaxant effect of PMAE appears to be non-specific of muscarinic or histaminic receptors, but may involve at least in part a mechanism of inhibition of the Ca(2+) influx into the smooth muscle cells through voltage-operated Ca(2+) channels.

Identification of new small molecule inhibitors of cystic fibrosis transmembrane conductance regulator protein: in vitro and in vivo studies

Cystic fibrosis transmembrane conductance regulator (CFTR) protein is a cAMP-regulated chloride channel that has been proposed as a pharmacological target to reduce intestinal fluid loss in cholera. The aim of this study was to identify new CFTR inhibitors by high-throughput screening. Screening of 50,000 drug-like small molecules was performed using a cell-based assay of iodide influx in Fisher rat thyroid (FRT) cells co-expressing human CFTR and halide-sensitive yellow fluorescent protein (YFP-H148Q). Two new CFTR inhibitors, 2-[N-(3-hydroxy-4-carboxyphenyl) amino]-4-(4-methylphenyl)-thiazole (INH 1) and 1-acetyl-5-bromo-2,3-dihydro-N-(1,2,3,4-tetrahydro-1-naphthalenyl)-1H-Indole-7-sulfonamide (INH 2), were identified. They were then determined for potency, reversibility and specificity by electrophysiological methods, and for in vivo efficacy in mouse model of cholera toxin-induced intestinal fluid secretion. INH 1 and INH 2 reversibly inhibited cAMP-activated apical chloride current in FRT cells with Kis of 15 and 20 microM, respectively. Similarly, in short-circuit current analysis in human colonic epithelial cell lines (T84 cells), cAMP-activated chloride secretion was inhibited by INH 1 and INH 2 with Kis of 24.5 and 25.3 microM, respectively. Calcium-activated chloride secretion in the T84 cells was markedly inhibited by 100 microM of INH 1, but was unaffected by 100 microM of INH 2. In vivo studies in mice showed that a single intraperitoneal injection of INH 1 (3 mg/kg) reduced cholera toxin-induced intestinal fluid secretion by 40%, whereas INH 2 produced no effect. Our results indicate that INH 1 could be a new class candidate for a blocker of cholera toxin-induced intestinal fluid secretion as well as a CFTR inhibitor.

Disinhibition of perifornical hypothalamic neurones activates noradrenergic neurones and blocks pontine carbachol-induced REM sleep-like episodes in rats

Studies in behaving animals suggest that neurones located in the perifornical (PF) region of the posterior hypothalamus promote wakefulness and suppress sleep. Among such cells are those that synthesize the excitatory peptides, orexins (ORX). Lack of ORX, or their receptors, is associated with narcolepsy/cataplexy, a disorder characterized by an increased pressure for rapid eye movement (REM) sleep. We used anaesthetized rats in which pontine microinjections of a cholinergic agonist, carbachol, can repeatedly elicit REM sleep-like episodes to test whether activation of PF cells induced by antagonism of endogenous, GABA(A) receptor-mediated, inhibition suppresses the ability of the brainstem to generate REM sleep-like state. Microinjections of the GABA(A) receptor antagonist, bicuculline (20 nl, 1 mm), into the PF region elicited cortical and hippocampal activation, increased the respiratory rate and hypoglossal nerve activity, induced c-fos expression in ORX and other PF neurones, and increased c-fos expression in pontine A7 and other noradrenergic neurones. The ability of pontine carbachol to elicit any cortical, hippocampal or brainstem component of the REM sleep-like response was abolished during the period of bicuculline-induced activation. The activating and REM sleep-suppressing effect of PF bicuculline was not attenuated by systemic administration of the ORX type 1 receptor antagonist, SB334867. Thus, activation of PF neurones that are endogenously inhibited by GABA(A) receptors is sufficient to turn off the brainstem REM sleep-generating network; the effect is, at least in part, due to activation of pontine noradrenergic neurones, but is not mediated by ORX type 1 receptors. A malfunction of the pathway that originates in GABA(A) receptor-expressing PF neurones may cause narcolepsy/cataplexy.

Migrastatin acts as a muscarinic acetylcholine receptor antagonist

Migrastatin and its analogs have various biological activities such as inhibition of cell migration and anchorage-independent growth of cancer cells. Although its biosynthesis and chemical synthesis have been under investigation, little is known about the biological target of migrastatin. Here, we found that migrastatin inhibited intracellular calcium mobilization induced by carbachol in neuroblastoma SK-N-SH cells without affecting Ca2+ mobilization and cAMP accumulation induced by ligands of other receptors. The binding of [3H] N-methylscopolamine, an antagonist for muscarinic receptor was also inhibited by migrastain. Functionally, migrastatin inhibited Ca2+ mobilization induced by carbachol in primary cultures of smooth muscle cells of rat bladder. This study reveals that migrastatin acts as a muscarinic acetylcholine receptor antagonist.

BXL-628, a vitamin D receptor agonist effective in benign prostatic hyperplasia treatment, prevents RhoA activation and inhibits RhoA/Rho kinase signaling in rat and human bladder

BACKGROUND

BXL-628 is a calcitriol analog shown to decrease prostate growth in preclinical and clinical studies. BPH symptoms are generated not only by prostate overgrowth but also by bladder overactivity, resulting from an increased RhoA/Rho-kinase signaling. Because bladder smooth muscle cells express VDR, we studied effects of BXL-628 on this pathway.

METHODS

RhoA and Rho-kinase gene expression and functional activity were studied in rat and human bladder smooth muscle by real-time RT-PCR, immuno-kinase assays, western blot analysis, confocal microscopy, in vitro contractility, and cell migration.

RESULTS

In bladder smooth muscle, carbachol responsiveness was delayed and Rho-kinase activity reduced by BXL-628 treatment because of impaired RhoA membrane translocation and activation. Accordingly, RhoA-mediated biological functions, such as cell migration and cytoskeleton remodeling were also inhibited by BXL-628.

CONCLUSIONS

BXL-628 inhibits RhoA/Rho-kinase signaling, a calcium sensitizing pathway, suggesting its possible clinical use in the treatment of altered bladder contractility often associated with BPH-induced lower urinary tract symptoms.

Blockade by NIP-142, an Antiarrhythmic Agent, of Carbachol-Induced Atrial Action Potential Shortening and GIRK1/4 Channel

Mechanisms for the atria-specific action potential-prolonging action of NIP-142 ((3R*,4S*)-4-cyclopropylamino-3,4-dihydro-2,2-dimethyl-6-(4-methoxyphenylacetylamino)-7-nitro-2H-1-benzopyran-3-ol), a benzopyran compound that terminates experimental atrial arrhythmia, was examined. In isolated guinea-pig atrial tissue, NIP-142 reversed the shortening of action potential duration induced by either carbachol or adenosine. These effects were mimicked by tertiapin, but not by E-4031. NIP-142 concentration-dependently blocked the human G protein-coupled inwardly rectifying potassium channel current (GIRK1/4 channel current) expressed in HEK-293 cells with an EC50 value of 0.64 microM. At higher concentrations, NIP-142 blocked the human ether a go-go related gene (HERG) channel current with an EC50 value of 44 microM. In isolated guinea-pig papillary muscles, NIP-142 had no effect on the negative inotropic effect of carbachol under beta-adrenergic stimulation, indicating lack of effect on the muscarinic receptor and Gi protein. These results suggest that NIP-142 directly inhibits the acetylcholine-activated potassium current.

Effect of rilmakalim on detrusor contraction in the presence and absence of urothelium

Openers of K(ATP) channels are known to inhibit KCl-, carbachol- and also electrically induced contractions in detrusor muscle strips from various species. Contractions of isolated strips of urinary bladder are usually of higher amplitude when the urothelium has been removed. This has been explained by the release of an urothelium-derived relaxing factor. In this study we examined whether intact urothelium may modulate the effect of the selective KATP channel opener rilmakalim. Contractile responses to 85 mM KCl and 10 microM carbachol were measured in detrusor strips from mouse, pig and man. In the presence of an intact urothelium, contractions were significantly reduced in strips from all three species investigated. In preparations with urothelium rilmakalim reduced KCl contractions with similar potency and efficacy [-logIC50 (M) 4.6 to 5.1; Effmax reduction to 14-30% of control]. However, in urothelium-denuded strips rilmakalim was more potent in pig (-logIC50 5.5) than in mouse and man (-logIC50 4.7 and 4.4, respectively). The order of potency for rilmakalim to suppress carbachol-induced contractions was pig (-logIC50 6.7)>man (5.8)>mouse (4.7); contractions were significantly more reduced in pig (Effmax reduction to 11+/-2%, n=10) and in mouse (21+/-2%, n=8) than in human detrusor (55+/-5%, n=5). The presence of urothelium did not affect the concentration-response curves for rilmakalim, with the exception of KCl-induced contractions in pig. Only the rilmakalim-induced relaxation of carbachol-mediated contractions in pig were prevented by the KATP channel blocker glibenclamide. We conclude that with this one exception, the responses to rilmakalim in detrusor contractions were not mediated by KATP channel opening.

Antimuscarinic agents exhibit local inhibitory effects on muscarinic receptors in bladder-afferent pathways

OBJECTIVES

To investigate the potential of antimuscarinic agents for sensory mechanisms in overactive bladder using intravesical instillation.

METHODS

Antimuscarinic agents were instilled intravesically in rats using two protocols. In the high-dose protocol, 5 mg atropine, oxybutynin, and dimethindene (M2-selective muscarinic receptor antagonist) were instilled into the bladder, and cystometric parameters, such as bladder capacity, intercontraction interval, pressure threshold, and maximal voiding pressure were monitored. In the low-dose protocol, 0.1 and 0.5 mug/mL oxybutynin, trospium, tolterodine, and dimethindene were continuously infused into the bladder. The doses chosen were based on the calculated urine-excreted concentrations of trospium typically achieved from human oral treatment of 40 mg/day. The effect of carbachol with and without the low-dose agents was then assessed.

RESULTS

With the high-dose protocol, bladder capacity, intercontraction interval, and pressure threshold were increased when atropine and oxybutynin were instilled, but not when dimethindene was used. The maximal voiding pressure was not affected by any of the agents tested. In the low-dose protocol, none of the cystometric parameters were altered with antimuscarinic agents alone. The intercontraction interval decreased with intravesical carbachol (65% +/- 0.1% compared with baseline), but this was prevented with concomitant antimuscarinic agents.

CONCLUSIONS

We have separated the local inhibitory effects of antimuscarinic agents during the storage phase from a decrease in voiding pressure. Intravesical instillation of antimuscarinic agents at clinically meaningful concentrations also suppressed carbachol-induced bladder overactivity. Antimuscarinic agents may be effective in treating overactive bladder, not only by suppression of muscarinic receptor-mediated detrusor muscle contractions, but also by blocking muscarinic receptors in bladder-afferent pathways.

Comparative study on pharmacological effects of DM-phencynonate hydrochloride and its optical isomers

AIM

The 3-azabicyclo(3,3,1)nonanyl-9-alpha-yl-alpha-cyclopentyl-alpha-phenyl-alpha-glycolate (DM-phencynonate hydrochloride, DMCPG) is a demethylated metabolite of 3-methyl-3-azabicyclo(3,3,1)nonanyl-9-alpha-yl-alpha-cyclopentyl-alpha-phenyl-alpha-glycolate (phencynonate hydrochloride, CPG). (+/-)DMCPG had one chiral center and two enantiomers [R(-) and S(+)DMCPG]. Here we carried out a comparative study of the pharmacological profiles of these optical isomers.

METHODS

Affinity and relative efficacy were tested using a radioligand-binding assay with muscarinic acetylcholine receptors from the rat cerebral cortex. Pharmacological activity was assessed in three individual experiments: (1) potentiating the effect of a sub-threshold hypnotic dose of sodium pentobarbital; (2) inhibiting oxotremorine-induced salivation; and (3) inhibiting the contractile response to carbachol.

RESULTS

In the competitive binding assay, R(-)DMCPG (K(i)=763.75 nmol/L) was 4- and 2-fold more potent than (+/-)DMCPG (K(i)=3186 nmol/L) and S(+)DMCPG (K(i)=1699 nmol/L) in inhibiting the binding of [(3)H]QNB. The R(-) and S (+) configurations showed positive cooperation (n(H)>1) with the muscarinic receptor, whereas (+/-)DMCPG had a negative cooperation (n(H)<1) relationship with the muscarinic receptor in a radio-binding assay. Both the R(-) and S(+) configurations could potentiate the effect of sub-threshold hypnotic dose of sodium pentobarbital in a dose-dependent manner (the ED(50) values were 2.53 and 18.65 mg/kg, respectively), but (+/-)DMCPG did not display significant central depressant effects at doses from 10 to 29.15 mg/kg (P>0.05). (+/-)DMCPG and its optical isomers suppressed the guinea pig ileum contractile response to carbachol. The IC(50) values were 7.78 x 10(-9), 1.88 x 10(-7), and 1.038 x 10(-7) nmol/L, respectively. In the anti-salivation study, (+/-)DMCPG and its enantiomers depressed oxotremorine- induced salivation in a dose-dependent manner, and the order of potency was R(-)DMCPG (ED(50)=0.44 mg/kg) > (+/-)DMCPG (ED(50)=2.88 mg/kg) >S(+)DMCPG (ED(50)=5.05 mg/kg).

CONCLUSION

(+/-)DMCPG and its optical isomers have differences in their pharmacological potencies as anticholinergic agents, and the R(-) configuration is more active than the S(+) configuration.

Methoctramine and gallamine inhibit PI hydrolysis in guinea-pig gallbladder

The present study aimed to determine the effect of two M2/M4-selective muscarinic receptor antagonists on blocking the hydrolysis of carbachol (CCh) stimulated phospho-inositide (PI) breakdown in order to address the possibility that a muscarinic receptor other than the M(3) receptor is involved in PI hydrolysis in this tissue. Gallbladder tissue slices labeled with myo-[2-3H] inositol were incubated with increasing concentrations of antagonists and agonist. After the reactions were terminated by the addition of chloroform/methanol, labeled inositol phosphates were separated using anion exchange chromatography. Muscarinic M2 antagonists methoctramine and gallamine both inhibited carbachol-induced PI breakdown at high concentrations, with log IC50 values of -5.145 and -6.049, respectively. Gallamine at 10(-5)M concentration failed to displace the dose-response curve for carbachol-induced accumulation of inositol triphosphate (IP3). Our data suggest that M(3) receptors play a major role in stimulation of PI hydrolysis in the guinea-pig gallbladder.

Excitatory effect of M1 muscarinic acetylcholine receptor on automaticity of mouse heart

We have investigated the effects of relatively high concentration of carbachol (CCh), an agonist of muscarinic acetylcholine receptor (mAChR), on cardiac automaticity in mouse heart. Action potentials from automatically beating right atria of mice were measured with conventional microelectrodes. When atria were treated with 100 microM CCh, atrial beating was immediately arrested and diastolic membrane potential (DMP) was depolarized. After exposure of the atria to CCh for approximately 4 min, action potentials were regenerated. The regenerated action potentials had lower frequency and shorter duration when compared with the control. When atria were pre-exposed to pirenzepine (1 microM), an M1 mAChR antagonist, there was complete inhibition of CCh-induced depolarization of DMP and regeneration of action potentials. Pre-exposure to AFDX-116 (11 ({2-[(diethylamino)-methyl]-1 -piperidyl}acetyl)-5,11 -dihydro-6H-pyridol[2,3-b][1,4] benzodiazepine-6-one base, 1 microM), an M2 mAChR antagonist, failed to block CCh-induced arrest of the beating. However, prolonged exposure to CCh elicited gradual depolarization of DMP and slight acceleration in beating rate. Our data indicate that high concentration of CCh depolarizes membrane potential and recovers right atrial automaticity via M1 mAChR, providing functional evidence for the role of M1 mAChR in the atrial myocytes.

Inhibitory mechanism of papaverine on carbachol-induced contraction in bovine trachea

We have demonstrated that the relaxing mechanism of papaverine in phasic muscles such as ileum, urinary bladder, and uterus is different from tonic muscles such as aorta. In this study, we examined the inhibitory mechanism of papaverine on carbachol (CCh)-induced contraction in the bovine trachea. Papaverine inhibited muscle contraction and increase in [Ca(2+)](i) level induced by CCh. Papaverine increased cAMP content but not cGMP content. Papaverine did not affect CCh-induced oxidized flavoproteins fluorescence or reduced pyridine nucleotides fluorescence. Papaverine (30 microM) remarkably inhibited muscle tension, but slightly decreased creatine phosphate and ATP contents. Iberiotoxin restored the inhibitions of muscle contraction and [Ca(2+)](i) level induced by papaverine or dibutyryl-cAMP. These results suggested that the relaxing mechanism of papaverine in the bovine trachea is mainly due to increases of cAMP content by inhibiting phosphodiesterase and the mechanism is partially involved in the activation of BK channel by cAMP.

Inhibitory effects of antipsychotics on carbachol-enhanced insulin secretion from perifused rat islets: role of muscarinic antagonism in antipsychotic-induced diabetes and hyperglycemia

Treatment with the atypical antipsychotics olanzapine and clozapine has been associated with an increased risk for deterioration of glucose homeostasis, leading to hyperglycemia, ketoacidosis, and diabetes, in some cases independent of weight gain. Because these events may be a consequence of their ability to directly alter insulin secretion from pancreatic beta-cells, we determined the effects of several antipsychotics on cholinergic- and glucose-stimulated insulin secretion from isolated rat islets. At concentrations encompassing therapeutically relevant levels, olanzapine and clozapine reduced insulin secretion stimulated by 10 micromol/l carbachol plus 7 mmol/l glucose. This inhibition of insulin secretion was paralleled by significant reductions in carbachol-potentiated inositol phosphate accumulation. In contrast, risperidone or ziprasidone had no adverse effect on cholinergic-induced insulin secretion or inositol phosphate accumulation. None of the compounds tested impaired the islet secretory responses to 8 mmol/l glucose alone. Finally, in vitro binding and functional data show that olanzapine and clozapine (unlike risperidone, ziprasidone, and haloperidol) are potent muscarinic M3 antagonists. These findings demonstrate that low concentrations of olanzapine and clozapine can markedly and selectively impair cholinergic-stimulated insulin secretion by blocking muscarinic M3 receptors, which could be one of the contributing factors to their higher risk for producing hyperglycemia and diabetes in humans.

Pharmacological profiles of an anticholinergic agent, phencynonate hydrochloride, and its optical isomers

AIM

To comparatively study the pharmacological profiles of 3-methyl-3-azabicyclo(3,3,1)nonanyl-9-alpha-yl-alpha-cyclopentyl-alpha-phenyl-alpha-glycolate (phencynonate hydrochloride, CPG), an anticholinergic agent, and its enantiomers [R(-)-and S(+)-CPG].

METHODS

The affinity and relative efficacy were tested using radioligand-binding assay with muscarinic acetylcholine receptors from rat cerebral cortex. The pharmacological activities were assessed in three individual experiments: (1) potentiating the effect of subthreshold hypnotic dose of sodium pentobarbital; (2) inhibiting oxotremorine-induced salivation; and (3) inhibiting the contractile response to carbachol.

RESULTS

The order of potency of phencynonate hydrochloride and its optical isomers to inhibit the binding of [3H]quinuclidinyl benzilate ([3H]QNB) was R(-)-CPG (K(i)=46.49+/-1.27 nmol/L)>CPG(K(i)=271.37+/-72.30nmol/L)>S(+)-CPG(K(i)=1263.12+/-131.64 nmol/L). The results showed that R(-)-CPG had the highest affinity to central muscarinic receptors among the three compounds, but did not show any central depressant effects at dose from 10.00 to 29.15 mg/kg. CPG increased the effects of subthreshold hypnotic dose of sodium pentobarbital induced-sleeping [the ED50+/-95% LC value was 21.06+/-3.04 mg/kg]. CPG and R(-)-CPG displayed nearly equipotent effect in depressing oxotremorine-induced salivation [the ED50 +/-95% LC for R(-) and CPG were 1.10+/-0.28 and 1.07+/-0.15 mg/kg, respectively], and the contractile response to carbachol (pA(2) values for R (-) and CPG were 6.84 and 6.80, respectively). S(+)-CPG presented the lowest anticholinergic profiles, but could potentate effects of its enantiomers in some manner.

CONCLUSIONS

These data suggested that R(-)-CPG acted as an eutomer in racemate and a competitive antagonist to acetylcholine muscarinic receptors, but S(+)-CPG was less active in comparison to R(-)-CPG and its racemate. The central depressant effects of R(-)-CPG and S(+)-CPG were lower in comparison to its racemate.

Inhibition of carbachol-evoked oscillatory currents by the NO donor sodium nitroprusside in guinea-pig ileal myocytes

The effect of sodium nitroprusside (SNP) on carbachol (CCh)-evoked inward cationic current (Icat) oscillations in guinea-pig ileal longitudinal myocytes was investigated using the whole-cell patch-clamp technique and permeabilized longitudinal muscle strips. SNP (10 microm) completely inhibited I(cat) oscillations evoked by 1 microm CCh. 1H-(1,2,4) Oxadiazole [4,3-a] quinoxaline-1-one (ODQ; 1 microm) almost completely prevented the inhibitory effect of SNP on Icat oscillations. 8-Bromo-guanosine 3',5'-cyclic monophosphate (8-Br-cGMP; 30 microm) in the pipette solution completely abolished Icat oscillations. However, a pipette solution containing Rp-8-Br-cGMP (30 microm) almost completely abolished the inhibitory effect of SNP on Icat oscillations. When the intracellular calcium concentration ([Ca2+]i) was held at a resting level using BAPTA (10 mm) and Ca2+ (4.6 microm) in the pipette solution, CCh (1 microm) evoked only the sustained component of Icat without any oscillations and SNP did not affect the current. A high concentration of inositol 1,4,5-trisphosphate (IP3; 30 microm) in the patch pipette solutions significantly reduced the inhibitory effect of SNP (10 microm) on Icat oscillations. SNP significantly inhibited the Ca2+ release evoked by either CCh or IP3 but not by caffeine in permeabilized preparations of longitudinal muscle strips. These results suggest that the inhibitory effects of SNP on Icat oscillations are mediated, in part, by functional modulation of the IP3 receptor, and not by the inhibition of cationic channels themselves or by muscarinic receptors in the plasma membrane. This inhibition seems to be mediated by an increased cGMP concentration in a protein kinase G-dependent manner.

Mechanisms responsible for the in vitro relaxation of a novel dibenzothiepine derivative (NSU-242) on tracheal and vascular smooth muscles

In our previous general screening experiments, we found that NSU-242, a dibenzothiepine derivative (1-10 mg/kg), inhibited antigen-induced immediate asthmatic response in actively sensitized guinea pigs in a dose-dependent manner. The purpose of the present study was to assess the mechanism of the relaxing effect of NSU-242 on smooth muscle contractions in isolated smooth muscle tissues of the porcine trachea and rat aorta. NSU-242 administration resulted in a concentration-dependent inhibition of the tracheal-tissue contractions induced by carbachol and high K(+) and the aortic-tissue contractions induced by norepinephrine and high K(+). The IC(50) values of these inhibitions were 1-10 microM, and there was no selectivity for the type of stimulation. In tracheal tissue, the relaxations were accompanied by neither changes in cAMP nor changes in cGMP. Carbachol (1 microM) and high K(+) (59.2 mM) increased myosin light chain (MLC) phosphorylation in the trachea, and NSU-242 (3-30 microM) had no effect on the level of MLC phosphorylation. Furthermore, NSU-242 (300 microM) had no effect on contractions in membrane-permeabilized tracheal tissue. FITC-phalloidin staining of the actin fiber in cultured vascular smooth muscle cells (A7r5) indicated that NSU-242 (10-100 microM) altered the configuration of actin stress fiber in the cytosol. However, unlike cytochalasin D, NSU-242 did not inhibit actin polymerization as assessed by in vitro assay. These results suggest that NSU-242 inhibits smooth muscle contractions without any effect on the Ca(2+)-dependent MLC phosphorylation. NSU-242 may uncouple the force generated by the activated actomyosin interaction, possibly by modifying the actin assembly in smooth muscle cells without a direct effect on actin molecules.

Regulatory volume increase after secretory volume decrease in colonic epithelial cells under muscarinic stimulation

To address the question of whether colonic secretory cells change their volume in response to carbachol (CCh) stimulation and, if so, the mechanisms involved therein, we used two-photon laser scanning microscopy to measure the volume of individual epithelial cells in the fundus region of crypts isolated from the guinea-pig distal colon. We also measured the volume of human colonic epithelial T84 cells using an electronic sizing technique. Both types of colonocytes responded to stimulation by CCh with shrinkage and then underwent a regulatory volume increase (RVI), even during continued stimulation by CCh. The secretory volume decrease (SVD) induced by CCh was antagonized by atropine, BAPTA loading and niflumic acid, a blocker of Ca(2+)-activated Cl(-) channels. An increase in the intracellular free [Ca(2+)] was observed with fura-2 during these volume responses to CCh. Removal of all Na(+) or K(+) or of most of the Cl(-) from the extracellular solution abolished the RVI, but not the preceding SVD. The RVI, but not the preceding SVD, was abolished by bumetanide, a blocker of the Na(+)-K(+)-2Cl(-) cotransporter. We conclude that guinea-pig crypt colonocytes and human T84 cells exhibit a cytosolic Ca(2+)-dependent SVD and undergo a subsequent RVI that is dependent on the operation of Na(+)-K(+)-2Cl(-) cotransporters.

Pertussis toxin-sensitive G protein but not NO/cGMP pathway mediates the negative inotropic effect of carbachol in adult rat cardiomyocytes

Previous studies have shown that muscarinic inhibition of cardiac contractility is mediated by either activation of nitric oxide (NO)/guanosine 3',5'-cyclic monophosphate (cGMP) pathway or stimulation of inhibitory G protein (G(i)). However, it still remains controversial as to whether NO/cGMP pathway or G(i) protein or both mediate(s) the negative inotropic effect of muscarinic agonists in adult ventricular myocytes. In the present study that involves the use of adult rat ventricular myocytes, the muscarinic agonist, carbachol, inhibited beta-adrenergic (isoproterenol) stimulation of contractility (cell shortening) by 82% and increased cGMP levels by 49% within 6 min. Pretreatment of myocytes with soluble guanylyl cyclase inhibitor (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, ODQ) or NO synthase inhibitor (N(G)-monomethyl-L-arginine, L-NMMA) for 30 min blocked carbachol-induced increases in cGMP levels. However, neither ODQ nor L-NMMA pretreatment had any effect on carbachol inhibition of isoproterenol-induced contractility. In addition, carbachol did not attenuate increases in myocyte contractility induced by forskolin (a direct activator of adenylyl cyclase) or 8-(4-chlorophenylthio)-adenosine 3',5'-cyclic monophosphate (a cell-permeable cAMP analog which activates cAMP-dependent protein kinase). Pretreatment of myocytes with G(i) protein inhibitor, pertussis toxin (PTX, 1 microg/ml), for 18-20 h abolished carbachol inhibition of isoproterenol-induced contractility. Furthermore, in ventricular myocytes isolated 3 days after in vivo treatment of rats with PTX (3 microg/100 g, i.p.), there was a complete loss of the negative inotropic effect of carbachol. These data indicate that pertussis toxin-sensitive G protein but not NO/cGMP pathway is required for muscarinic inhibition of beta-adrenoceptor-mediated increases in contractility in adult rat ventricular myocytes.

Wine polyphenols induce hypotension, and decrease cardiac reactivity and infarct size in rats: involvement of nitric oxide

1. The effects of short-term oral administration of red wine polyphenolic compounds (RWPC, 20 mg x kg(-1) day(-1) for 7 days) on haemodynamics, ex vivo cardiac responsiveness and ischaemia-reperfusion injury were investigated in rats. The involvement of nitric oxide (NO) was evaluated using the NO synthase inhibitor, N(G)-nitro-l-arginine methyl ester (l-NAME, 2 mg x kg(-1) day(-1) for 7 days), at a dose which did not affect blood pressure. 2. Ex vivo reactivity of hearts from RWPC-treated rats showed lower basal developed pressure, greater heart rate and decreased inotropic responses to either beta-adrenoceptor or muscarinic receptor stimulation with isoprenaline or carbachol, respectively.3. RWPC treatment did not modify cardiac expression of endothelial NO synthase or Cu/Zn superoxide dismutase. However, it increased nitrite in the coronary effluent. 4. In ischaemia-reperfusion, RWPC treatment reduced infarct size and oxidative stress, as shown by the myocardial content of the end products of lipid peroxidation, malondialdehyde and 4-hydroxynonenal, without affecting post-ischaemic contractile dysfunction. All the observed effects of RWPC were prevented by l-NAME treatment. 5. Altogether, these data show that short-term treatment with RWPC decreases blood pressure and cardiac responsiveness, and protects against post-ischaemic infarction via decreased oxidative stress. All the above effects of RWPC are sensitive to NO synthase inhibition that implies an involvement of NO-dependent pathway. This study suggests a basis for the beneficial effects of plant-derived polyphenols against cardiovascular disease.

Mechanisms involved in carbachol-induced Ca(2+) sensitization of contractile elements in rat proximal and distal colon

1. Mechanisms involved in Ca(2+) sensitization of contractile elements induced by the activation of muscarinic receptors in membrane-permeabilized preparations of the rat proximal and distal colon were studied. 2. In alpha-toxin-permeabilized preparations from the rat proximal and distal colon, Ca(2+) induced a rapid phasic and subsequent tonic component. After Ca(2+)-induced contraction reached a plateau, guanosine 5'-triphosphate (GTP) and carbachol (CCh) in the presence of GTP further contracted preparations of both the proximal and distal colon (Ca(2+) sensitization). Y-27632, a rho-kinase inhibitor, inhibited GTP plus CCh-induced Ca(2+) sensitization more significantly in the proximal colon than in the distal colon. 3. Y-27632 at 10 microm had no effect on Ca(2+)-induced contraction or slightly inhibited phorbol-12,13-dibutyrate-induced Ca(2+) sensitization in either proximal or distal colon. Chelerythrine, a protein kinase C inhibitor, inhibited GTP plus CCh-induced Ca(2+) sensitization in the distal colon, but not in the proximal colon. The component of Ca(2+) sensitization that persisted after the chelerythrine treatment was completely inhibited by Y-27632. 4. In beta-escin-permeabilized preparations of the proximal colon, C3 exoenzyme completely inhibited GTP plus CCh-induced Ca(2+) sensitization, but PKC(19-31) did not. In the distal colon, C3 exoenzyme abolished GTP-induced Ca(2+) sensitization. It inhibited CCh-induced sensitization by 50 % and the remaining component was inhibited by PKC(19-31). 5. These results suggest that both protein kinase C and rho pathways in parallel mediate the Ca(2+) sensitization coupled to activation of muscarinic receptors in the rat distal colon, whereas the rho pathway alone mediates this action in the proximal colon.

Pharmacological effects of darifenacin on human isolated urinary bladder

Darifenacin [(S)-2--2,2-diphenylacetamide] is a novel antimuscarinic drug currently undergoing phase III trials for the treatment of overactive bladder. We investigated the functional antagonist potency of darifenacin, and the antimuscarinic drugs propiverine, oxybutynin and atropine, on human detrusor smooth muscle. Urinary bladder specimens were obtained from 20 patients who underwent total cystectomy for malignant bladder tumor. Using an organ-bath technique, the effects of the compounds on carbachol-, KCl-, CaCl(2)- or electrical field stimulation (EFS)-induced contractions of the tissues were evaluated. The order of antagonist potency (pA(2 )values) at the muscarinic M(3) receptors was: darifenacin (9.34) > atropine (9.26) > oxybutynin (7.74) > propiverine (7.68). Darifenacin and atropine, at concentrations up to 10(-6) mol/l, did not inhibit the KCl- and CaCl(2)-induced contractions (concentrations 80 and 5 mmol/l, respectively), while propiverine and oxybutynin (10(-5) mol/l) significantly inhibited these contractions. Pretreatment with darifenacin (10(-9)-10(-6) mol/l), propiverine (10(-8)- 10(-5) mol/l), oxybutynin (10(-8)-10(-5) mol/l) and atropine (10(-9)-10(-6) mol/l) significantly inhibited maximum EFS-induced contractions. Darifenacin inhibited contractions of human detrusor smooth muscle only through its antimuscarinic action, while propiverine and oxybutynin had both antimuscarinic and Ca(2+) channel antagonist actions. These findings indicate that darifenacin is a potent antagonist at the M(3) receptor and support its use as a treatment for overactive bladder.

Phenotypic differences in cholinergic responses of distal colonic epithelium

The Flinders sensitive line (FSL) rats exhibit an increased cholinergic responsiveness in vivo when compared to their counterparts, the Flinders resistant line (FRL) rats. The functional consequences of this phenotypic difference on colonic mucosal function are not known. We sought to determine whether isolated distal colonic mucosa from the two strains exhibit differential responses to cholinergic agonists. The responses of the distal colonic mucosa from two lines of rats to carbachol were compared by recording changes in short-circuit current. The ion movements associated with these changes were assessed by flux analysis of the radiotracers, 22Na and 36Cl. The anticipated hyper-responsiveness to cholinergic stimulation in FSL rats was not seen. Carbachol responses were significantly enhanced by indomethacin pretreatment only in FRL rats. Tetrodotoxin (TTX) pretreatment significantly reduced responses to carbachol in FSL rats at all concentrations tested, though this was only seen with lower concentrations in FRL rats. Flux analysis indicated that both lines absorbed Na+ and Cl- under basal conditions and that a significant residual flux was present. Stimulation with carbachol led to significant reductions in net Na+ and Cl- fluxes in both lines. The changes in net Na+ and Cl- flux in both lines stem largely from a decrease in mucosal to serosal fluxes of both ions with an increase in serosal to mucosal flux of Cl-. The striking difference is the significant reduction in residual flux seen only in FRL rats. Indomethacin pretreatment abolished the changes in residual flux seen in FRL rats. Thus the responses to carbachol in these rats had at least three components: (a) a direct effect on the transporting colonocyte, (b) an indirect effect mediated by an arachidonic acid metabolite, and (c) another indirect effect involving a neurotransmitter. The relative contributions of each of these components were different in the two lines.

Phospholipase C, but not InsP3 or DAG, -dependent activation of the muscarinic receptor-operated cation current in guinea-pig ileal smooth muscle cells

1. In visceral smooth muscles, both M(2) and M(3) muscarinic receptor subtypes are found, and produce two major metabolic effects: adenylyl cyclase inhibition and PLCbeta activation. Thus, we studied their relevance for muscarinic cationic current (mI(CAT)) generation, which underlies cholinergic excitation. Experiments were performed on single guinea-pig ileal cells using patch-clamp recording techniques under conditions of weakly buffered [Ca(2+)](i) (either using 50 microm EGTA or 50-100 microm fluo-3 for confocal fluorescence imaging) or with [Ca(2+)](i) 'clamped' at 100 nm using 10 mm BAPTA/CaCl(2) mixture. 2. Using a cAMP-elevating agent (1 microm isoproterenol) or a membrane-permeable cAMP analog (10 microm 8-Br-cAMP), we found no evidence for mI(CAT) modulation through a cAMP/PKA pathway. 3. With low [Ca(2+)](i) buffering, the PLC blocker U-73122 at 2.5 microm almost abolished mI(CAT), in some cases without any significant effect on [Ca(2+)](i). When [Ca(2+)](i) was buffered at 100 nm, U-73122 reduced both carbachol- and GTPgammaS-induced mI(CAT) maximal conductances (IC(50)=0.5-0.6 microm) and shifted their activation curves positively. 4. U-73343, a weak PLC blocker, had no effect on GTPgammaS-induced mI(CAT), but weakly inhibited carbachol-induced current, possibly by competitively inhibiting muscarinic receptors, since the inhibition could be prevented by increasing the carbachol concentration to 1 mm. Aristolochic acid and D-609, which inhibit PLA(2) and phosphatidylcholine-specific PLC, respectively, had no or very small effects on mI(CAT), suggesting that these enzymes were not involved. 5. InsP(3) (1 microm) in the pipette or OAG (20 microm) applied externally had no effect on mI(CAT) or its inhibition by U-73122. Ca(2+) store depletion (evoked by InsP(3), or by combined cyclopiazonic acid, ryanodine and caffeine treatment) did not induce any significant current, and had no effect on mI(CAT) in response to carbachol when [Ca(2+)](i) was strongly buffered to 100 nm. 6. It is concluded that phosphatidylinositol-specific PLC modulates mI(CAT) via Ca(2+) release, but also does so independently of InsP(3), DAG, Ca(2+) store depletion or a rise of [Ca(2+)](i). Our present results explain the previously established 'permissive' role of the M(3) receptor subtype in mI(CAT) generation, and provide a new insight into the molecular mechanisms underlying the shifts of the cationic conductance activation curve.

PDE4D plays a critical role in the control of airway smooth muscle contraction

The airways of mice deficient in the cAMP phosphodiesterase PDE4D gene are refractory to muscarinic cholinergic stimulation. This study was undertaken to determine whether altered smooth muscle contractility causes the PDE4D-/- phenotype. A major disruption in contractility was observed in isolated PDE4D-/- tracheas, with a 60% reduction in maximal tension and a fivefold decrease in sensitivity to muscarinic cholinergic agonists. Conversely, responses to KCl or arginine vasopressin were unaffected. PDE4D is the predominant PDE4 form in tracheal extracts and PDE4D mRNA is expressed in smooth muscle where muscarinic binding sites are most abundant. Cyclic AMP accumulation in response to acute G(s)alpha-coupled receptor stimulation was increased up to fourfold in the airway of PDE4D-/- mice when compared with wild-type. This increase in cAMP was associated with an increased sensitivity to PGE2-induced relaxation of the PDE4D-/-tracheas. Furthermore, a blockade of prostanoid accumulation in PDE4D-/- tracheas restored the response to muscarinic cholinergic stimulation in vitro and in vivo. These results demonstrate that PDE4D plays a key role in balancing relaxant and contracting cues in airway smooth muscle, suggesting that natural mutations in the PDE4D gene have profound effects on airway tone.

Isoflurane Reduction of Carbachol-evoked Cytoplasmic Calcium Transients Is Dependent on Caffeine-sensitive Calcium Stores

Background

Many muscarinic functions are relevant to anesthesia, and alterations in muscarinic activity affect the anesthetic/analgesic potency of various drugs. Volatile anesthetics have been shown to depress muscarinic receptor function, and inhibition of the muscarinic signaling pathway alters the minimal alveolar anesthetic concentration of inhaled anesthetics. The purpose of this investigation was to determine in a neuronal cell which source of Ca2+ underlying the carbachol-evoked transient increase in cytoplasmic Ca2+ was reduced by isoflurane.

Methods

Experiments were performed at 37 degrees C on continuously perfused monolayers of human neuroblastoma SH-SY5Y cells using Fura-2 as the cytoplasmic Ca2+ indicator. Carbachol (1 mm) was applied to evoke a transient increase in cytoplasmic Ca2+.

Results

Isoflurane (1 mm) reduces the carbachol-evoked transient increase in cytoplasmic Ca2+, and this isoflurane action is eliminated when the cells are continuously stimulated with 200 mm KCl or pretreated with 10 mm caffeine or 200 microm ryanodine.

Conclusions

Isoflurane reduction of the carbachol-evoked transient increase in cytoplasmic Ca2+ requires full caffeine-sensitive Ca2+ stores and Ca2+ release from the caffeine-sensitive stores through the ryanodine-sensitive Ca2+ release channels. The results indicate that isoflurane interferes with a muscarinic Ca2+ signaling through a mechanism downstream from the muscarinic receptors.

Age-related smooth muscle reactivity changes in the rat bladder: an in vitro study

An experimental study was conducted to investigate developmental changes of the rat detrusor smooth muscle (DSM) reactivity from newborn to adult period. Urinary bladders were obtained from adult (4 months old), 1-month-old and newborn (4-7 days old) male Sprague-Dawley rats. DSM reactivity of the three groups was evaluated in organ chambers. The newborn DSM strips revealed markedly increased purinoceptor- and cholinoceptor-mediated contractions (ATP, carbachol) with increased maximum response (2.98- and 8.96-fold increase for ATP, 2.90- and 4.22-fold increase for carbachol, when the newborn bladder compared with 1-month-old and adult groups, respectively) and sensitivity (1.65- and 1.29-fold increase for ATP when the newborn bladder compared with the 1-month-old and adult groups, respectively). Additionally the maximum contractile response to KCl in the bladder from the newborn was 1.65- and 8.96-fold increased compared to bladders of the 1-month-old and adult groups, respectively. However, no significant changes in the adrenoceptor-mediated relaxation (isoproterenol) of the rat DSM were observed among the groups. These results indicate that development alters the in vitro responsiveness of rat DSM. The newborn rat bladder gains some of the adult bladder properties within 1 month. These changes are likely to reflect the changing role of parasympathetic regulation in the DSM reactivity during development of the rat bladder.

Existence of functional M3-muscarinic receptors in the human heart

It has been recently shown that, in adult rat ventricular cardiomyocytes, functional muscarinic receptors (M-receptors) of the M(3)-subtype exist that mediate inositol phosphate (IP) formation. The aim of this study was to characterize the M-receptor subtype mediating IP formation in the human heart. For this purpose in [3H]-myo-inositol labeled slices of human right atria, carbachol-induced [3H]-IP formation and its inhibition by several M-receptor antagonists was assessed. Carbachol (0.1 microM-100 microM) increased [3H]-IP formation; maximal increase at 100 microM was 93+/-16% above basal ( n=20); the pEC(50)-value for carbachol was 5.56. Atropine (1 microM) completely suppressed 100 microM carbachol-induced [3H]-IP formation. Among the M-receptor subtype "selective" antagonists himbacine (1 microM) and pirenzepine (1 microM) only marginally affected carbachol-induced [3H]-IP formation whereas the M(3)-receptor antagonist darifenacin (1 nM-1 microM) concentration-dependently inhibited carbachol-induced [3H]-IP formation with a pK(i)-value of 8.49. We conclude that in human right atrium there exist functional M(3)-receptors that couple to IP formation.

Ethanol blocks both basic fibroblast growth factor- and carbachol-mediated neuroepithelial cell expansion with differential effects on carbachol-activated signaling pathways

We have expanded neuroepithelial cells dissociated from the embryonic rat telencephalon in serum-free defined medium containing basic fibroblast growth factor (bFGF) in order to generate a model neuroepithelium to study the interaction of ethanol with both growth factor- and transmitter-stimulated proliferation. Ethanol blocked proliferation stimulated by bFGF and by carbachol, an agonist at muscarinic acetylcholine receptors, in a dose-dependent manner. In addition, ethanol attenuated autonomous expansion of neuroepithelial cells occurring following withdrawal of bFGF. The latter effect was associated with an increase in the number of apoptotic cells identified by terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling labeling. We studied the effects of ethanol on carbachol-stimulated signaling pathways critical to its proliferative effects. Ethanol significantly reduced carbachol-stimulated Ca(2+) signaling, as well as Erk1/Erk2, Akt and cyclic AMP-response element-binding phosphorylations in a dose-dependent manner. Comparison of the potency of ethanol in attenuating carbachol-stimulated proliferation and signal transduction showed that mitogen-activated protein kinase phosphorylation was less sensitive to ethanol than the other parameters. The results indicate that ethanol's suppression of proliferation induced by carbachol in this model neuroepithelium likely involves multiple signaling pathways. These effects in vitro may help to explain the devastating effects of prenatal ethanol exposure in vivo, which contribute to the fetal alcohol syndrome.

Islet amyloid polypeptide inhibits glucagon release and exerts a dual action on insulin release from isolated islets

We have studied the influence of a wide concentration range of islet amyloid polypeptide (IAPP) on both glucagon and insulin release stimulated by various types of secretagogues. In an islet incubation medium devoid of glucose, the rate of glucagon release being high, we observed a marked suppressive action by low concentrations of IAPP, 10(-10) and 10(-8) M, on glucagon release. Similarly, glucagon release stimulated by L-arginine, the cholinergic agonist carbachol, or the phosphodiesterase inhibitor isobutylmethyl xanthine (IBMX), an activator of the cyclic AMP system, was inhibited by IAPP in the 10(-10) and 10(-8) M concentration range. Moreover, basal glucagon release at 7 and 10 mM glucose was suppressed by IAPP. In contrast, IAPP exerted a dual action on insulin release. Hence, low concentrations of IAPP brought about a modest increase of basal insulin secretion at 7 mM glucose and also of insulin release stimulated by carbachol. High concentrations of IAPP, however, inhibited insulin release stimulated by glucose (10 and 16.7 mM), IBMX, carbachol and L-arginine. In conclusion, our data suggest that IAPP has complex effects on islet hormone secretion serving as an inhibitor of glucagon release and having a dual action on insulin secretion exerting mainly a negative feedback on stimulated and a positive feedback on basal insulin release.

Mast cell stabilization, lipoxygenase inhibition, hyaluronidase inhibition, antihistaminic and antispasmodic activities of Aller-7, a novel botanical formulation for allergic rhinitis

Allergic rhinitis, also known as hay fever, rose fever or summer catarrh, is a major challenge to health professionals. A large number of the world's population, including approximately 40 million Americans, suffers from allergic rhinitis. A novel, botanical formulation (Aller-7) has been developed for the treatment of allergic rhinitis using a combination of extracts from seven medicinal plants, including Phyllanthus emblica, Terminalia chebula, T. bellerica, Albizia lebbeck, Piper nigrum, Zingiber officinale and P. longum, which have a proven history of efficacy and health benefits. The clinical manifestations of allergy are due to a number of mediators that are released from mast cells. The effect of Aller-7 on rat mesenteric mast cell degranulation was studied by incubating different concentrations of Aller-7 and challenging them with a degranulating agent, compound 48/80. The inhibitory activity of Aller-7 was determined against lipoxygenase and hyaluronidase, the key enzymes involved in the initiation and maintenance of inflammatory responses. Furthermore, most of these manifestations are due to histamine, which causes vasodilatation, increasing capillary permeability and leading to bronchoconstriction. Hence, the antihistaminic activity of Aller-7 was determined is isolated guinea pig ileum substrate using cetirizine as a positive control. The antispasmodic effect of Aller-7 on contractions of guinea pig tracheal chain was determined using papaverine and cetirizine as controls. Aller-7 exhibited potent activity in all these in vitro models tested, thus demonstrating the novel anti-allergic potential of Aller-7.

Regulation of carbachol-induced c-fos mRNA expression in AR42J cells by somatostatin receptor subtypes 1, 2, and 3

INTRODUCTION

Somatostatin is an inhibitory peptide that exerts its effects tissue-specifically by activating one or more of five receptors (SSTR 1-5). Although several studies have examined which SSTR subtypes control gastrointestinal function, effects of somatostatin on pancreatic gene expression are not well defined.

AIM

To examine the effects of somatostatin and newly synthesized selective SSTR agonists on the cholinergically stimulated expression of the immediate early response gene

METHODOLOGY AND RESULTS

In pancreatic acinar AR42J cells, polymerase chain reaction analysis revealed that mRNAs for SSTR 1, 2, and 3 were expressed. SSTR 4 and 5 were not detected. When AR42J cells were exposed to the cholinergic agonist carbachol in the presence of somatostatin or selective SSTR agonists, significant and dose-dependent reductions in agonist-induced levels of mRNA were noted. Pretreatment with agonists specific for SSTR 4 or 5 had no inhibitory effects. The inhibitory actions of somatostatin were pertussis toxin-sensitive. In addition, since somatostatin did not affect intracellular calcium homeostasis, the inhibitory actions of somatostatin are independent of calcium signaling.

CONCLUSION

The current studies demonstrate that somatostatin inhibits carbachol-induced increases in expression by interacting with somatostatin receptor subtypes 1, 2, and 3. In addition, because somatostatin did not affect intracellular calcium homeostasis, it can be concluded that SSTR actions are independent of carbachol-stimulated calcium signaling.

S-Isopetasin, a sesquiterpene of Petasites formosanus, allosterically antagonized carbachol in isolated guinea pig atria

We investigated the antimuscarinic effect of S-isopetasin in isolated guinea pig atria to clarify whether it preferentially acts on muscarinic M 2 or M 3 receptors. The tension changes of isolated atria were isometrically recorded on a polygraph. S-Isopetasin at 50 and 100 microM significantly inhibited baselines of contractile tension and heart rate, but atropine at 1 microM enhanced both. S-Isopetasin (10 - 100 microM) did not significantly alter the concentration-negative inotropic response curves of carbachol (CCh) in left atria. S-Isopetasin (10 - 100 microM) allosterically antagonized negative inotropic and chronotropic responses induced by CCh in spontaneously beating right atria, based on the slopes of Schild plots significantly differing from unity. On the contrary, atropine (0.01 - 1 microM) competitively antagonized all the above responses to CCh. The pA 2 values of S-isopetasin were significantly less than that of S-isopetasin in guinea pig trachealis, suggesting that S-isopetasin may preferentially act on tracheal muscarinic M 3, but not cardiac muscarinic M 2 receptors. However, atropine preferentially acts neither. This finding reveals that S-isopetasin may have benefit in the treatment of asthma.

Different actions of protein kinase C isoforms alpha and epsilon on gastric acid secretion

1. The phorbol ester TPA, an activator of protein kinase C (PKC), inhibits cholinergic stimulation of gastric acid secretion but increases basal H(+) secretion. 2. Since these contradictory findings suggest the action of different PKC isozymes we analysed the role of calcium-dependent PKC-alpha, and calcium-independent PKC-epsilon in gastric acid secretion. 3. Inhibition of PKC-alpha by the indolocarbazole Gö 6976 revealed that about 28% of carbachol-induced acid secretion was inhibited by PKC-alpha. In the presence of Gö 6976 approximately 64% of the carbachol-induced signal transduction is mediated by Ca(2+)/calmodulin-dependent protein kinase II (CaMKII), and 14% is conveyed by PKC-epsilon as deduced from the inhibition with the bisindolylmaleimide Ro 31-8220. 4. Inhibition of carbachol-induced acid secretion by TPA was accompanied by a decrease in CaMKII activity. 5. The stimulation of basal acid secretion by TPA was biphasic with a peak at a very low concentration (10 pM), resulting in an activation of the calcium-sensor CaMKII. The activation was determined with a phosphospecific polyclonal antibody against active CaMKII. The TPA-induced increase of H(+) secretion was sensitive to the cell-permeable Ca(2+)-chelator BAPTA/AM, Ro 31-8220, and the CaMKII-inhibitor KN-62, but not to Gö 6976. 6. Since TPA induced the translocation of PKC-epsilon but not of PKC-alpha in resting parietal cells, PKC-epsilon seems to be at least responsible for an initial elevation of free intracellular calcium to initiate TPA-induced acid secretion. 7. Our data indicate the different roles of two PKC isoforms: PKC-epsilon activation appears to facilitate cholinergic stimulation of H(+)-secretion likely by increasing intracellular calcium. In contrast, PKC-alpha activation attenuates acid secretion accompanied by a down-regulation of CaMKII activity.

Direct inhibitory effect of erythromycin on human alimentary tract smooth muscle

BACKGROUND

Erythromycin was found to stimulate motor activity in the upper gastrointestinal tract. However, in several smooth muscle preparations, it also elicited an inhibitory effect. Our aim was to study the effect of erythromycin in various human alimentary tract smooth muscles.

METHODS

Using force measurements, we assessed the effect of erythromycin on electrically and chemically evoked contractions of isolated muscle strips of human gallbladder, small intestine, and colon.

RESULTS

The muscarinic receptor agonist carbachol evoked contraction in gallbladder, ileum, and colonic smooth muscle that were reduced by erythromycin at 10(-4) M to 72% +/- 24%, 77% +/- 22%, and 76% +/- 22% of control values, respectively. Erythromycin did not affect contractions evoked by noncholinergic agents. Erythromycin's inhibitory effects were not altered by nerve blockade, indicating a direct muscle effect. Eryrthromycin also reduced contractions evoked by electrical stimulation at frequencies of 5, 10, and 20 Hz in the human gallbladder, ileum, and colon preparations. These contractions were reduced by erythromycin in a reversible and dose-dependent manner.

CONCLUSIONS

Erythromycin antagonized direct cholinergic effects on various smooth muscles from the human alimentary tract in a concentration-dependent manner.

CaMKII is activated and translocated to the secretory apical membrane during cholinergically conveyed gastric acid secretion

The Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) is thought to be activated during the cholinergic stimulation of gastric acid secretion. The carbachol-induced acid production of cultured rabbit parietal cells was dose-dependently inhibited by the CaMKII inhibitor KN-62 as measured by accumulation of the weak base [(14)C]aminopyrine ([(14)C]-AP). Inhibition by KN-62 was most efficient at concentrations of carbachol >10(-6) M. After carbachol stimulation, we observed an activation of CaMKII activity, and its translocation to the apical membrane of gastric mucosal cells. We found a doubling of the abundance of CaMKII to the stimulus-associated apical membrane (SA vesicles) compared to the apical membrane from the resting state after carbachol induction. This was shown by both an anti-CaMKII serum and the 1.8-fold increase of the CaMKII phosphotransferase activity in vitro. The SA vesicles exhibited a strong increase of autoactivated CaMKII probed with an anti-autoactivated CaMKII antibody. Additionally, we observed a colocalization of both CaMKII and the H(+)-K(+)-ATPase of SA vesicles similar to the colocalization of both enzymes to the tubulovesicles suggesting them as at least one pool for the SA vesicular CaMKII. Our data indicate that the activation of CaMKII and the carbachol-dependent redistribution of CaMKII to the SA vesicles are distinct processes that occur in parallel to regulate the activity and localization of CaMKII. These findings contribute to the model implicating an involvement for CaMKII in the intracellular dynamics of the acid secretion.

Doxorubicin affects the cardiac muscarinic system in the rat

During the study on the mechanism of doxorubicin-induced cardiotoxicity, we observed that a long incubation (4 hr) with doxorubicin reduced the maximal negative inotropic effects of a muscarinic receptor agonist, carbachol. The mechanism responsible for this doxorubicin-induced reduction of the efficacy of carbachol was examined in isolated guinea pig hearts. In isolated left atrial muscle preparations, 1 hr incubation with 100 microM doxorubicin caused a parallel right-ward shift of the concentration-response curves for carbachol, but a longer (4 hr) incubation with this agent (30, 100 or 200 microM), caused a significant reduction of the magnitude of the negative inotropic effect of carbachol in addition to the concentration-dependent parallel right-ward shift. The 4-hr incubation with these concentrations of doxorubicin also reduced the maximal negative inotropic effect of an adenosine A1 receptor agonist, R-phenylisopropyl adenosine (R-PIA), without affecting the potency of this agonist. Doxorubicin (1 to 100 microM) reduced [3H]quinuclidinyl benzilate (QNB) binding in a concentration dependent manner, but failed to alter [3HIR-PIA binding. The decrease in the magnitude of the maximal negative inotropic effect by doxorubicin was caused by changes in the muscarinic system at steps common to the transduction of muscarinic and adenosine A1 receptor mechanisms.

Spasmolytic effects of three harmala alkaloids on guinea-pig isolated trachea

The present study examined and compared the spasmolytic effects of 3 harmala alkaloids, harmine, harman, and harmaline, on carbachol-, histamine-, and KCl-induced contractions of guinea-pig isolated tracheal preparations. All 3 compounds relaxed the tracheal preparations contracted by these spasmogens with similar or different EC50 values, harmine being the most potent one. The cumulative concentration-response curves of all 3 compounds for carbachol-induced contraction were shifted to the right by propranolol (1 microM) pretreatment, indicating the involvement of the activation on the beta-adrenoceptors. All 3 compounds shifted the concentration-response curves of carbachol to the right in a parallel manner with the pA2 values comparable with their relaxation EC50 values, indicating a competitive antagonism at the muscarinic receptors. Receptor binding assays indicated that all 3 compounds interacted with lung muscarinic receptors (Ki = 11-13 microM), histamine H1 receptors (Ki = 27-107 microM), and beta2-adrenoceptors (Ki = 20-51 microM). Therefore, in addition to their actions on receptor-linked and voltage-dependent Ca2+ channels as reported in other types of smooth muscle, the present study suggests that the actions on muscarinic receptors, histamine H1 receptors, and beta2-adrenoceptors are also involved in their spasmolytic effects on airway smooth muscles.

Blood-brain barrier preservation in the in vitro isolated guinea pig brain preparation

The morphofunctional preservation of the blood-brain barrier (BBB) was evaluated in the isolated guinea pig brain maintained in vitro by arterial perfusion. Electron microscopy evaluation after 5 hr in vitro demonstrated that cerebral capillaries and BBB specializations in this preparation retain features compatible with structural integrity. BBB-impermeable and -permeable atropine derivatives arterially perfused to antagonize carbachol-induced fast oscillatory activity confirmed the functional preservation of the BBB in vitro. To study BBB function further, changes in extracellular K+ concentration during arterial perfusion of a high-K+ solution were measured with K+-sensitive electrodes positioned in the cortex and, as control, at the brain venous outlet, where the solution perfused through the brain arterial system was collected. After 5 hr in vitro, the [K+](o) values measured during high-K+ perfusion in the piriform and entorhinal cortices were 5.02 +/- 0.17 mM (mean +/- SE) and 5.2 +/- 0.21 mM, respectively (n = 6). Coperfusion of the high-K+ solution with the Na+/K+ pump blocker ouabain (10 microM; n = 4) induced consistently spreading depression preceded by a rise in [K+](o). Finally, sporadic, isolated spots of extravasation of the fluorescent marker fluorescein isothiocyanate (FITC)-dextran preferentially circumscribed to deep cortical layers was observed in brains perfused with FITC-dextran after 5 hr in vitro. The study demonstrates that the in vitro isolated guinea pig brain is viable for studying cerebrovascular interactions and BBB permeability of compounds active in the central nervous system.

Phospholamban regulation of bladder contractility: evidence from gene-altered mouse models

1. Phospholamban (PLB) is an inhibitor of the sarcoplasmic reticulum (SR) Ca2+-ATPase (SERCA). Its presence and/or functional significance in contractility of bladder, a smooth muscle tissue particularly dependent on SR function, is unknown. We investigated this by measuring the effects of carbachol (CCh) on force and [Ca2+]i in bladder from mice in which the PLB gene was ablated (PLB-KO mice). In the PLB-KO bladder, the maximum increases in [Ca2+]i and force were significantly decreased (41.5 and 47.4 % of WT), and the EC50 values increased. 2. Inhibition of SERCA with cyclopiazonic acid (CPA) abolished these differences between WT and PLB-KO bladder, localizing the effects to the SR. 3. To determine whether these effects were specific to PLB, we generated mice with smooth-muscle-specific expression of PLB (PLB-SMOE mice), using the SMP8 alpha-actin promoter. Western blot analysis of PLB-SMOE mice showed approximately an eightfold overexpression of PLB while SERCA was downregulated 12-fold. 4. In PLB-SMOE bladders, in contrast, the response of [Ca2+]i and force to CCh was significantly increased and the EC50 values were decreased. CPA had little affect on the CCh-induced increases in [Ca2+]i and force in PLB-SMOE bladder. 5. These results show that alteration of the PLB:SERCA ratio can significantly modulate smooth muscle [Ca2+]i. Importantly, our data show that PLB can play a major role in modulation of bladder contractility.

Inhibition of carbachol stimulated acid secretion by interleukin 1beta in rabbit parietal cells requires protein kinase C

BACKGROUND

Interleukin 1beta (IL-1beta) is a potent inhibitor of gastric acid secretion. Regulatory actions at several levels have previously been demonstrated, including direct inhibition of parietal cell acid secretion. Although IL-1beta may activate several intracellular signalling pathways, the mechanisms responsible for inhibition of carbachol stimulated acid secretion have not been determined.

AIMS

To investigate the roles of protein kinase C (PKC) and the sphingomyelinase signalling pathways in the regulation of acid secretion by IL-1beta.

METHODS

Rabbit parietal cells were obtained by collagenase-EDTA digestion and centrifugal elutriation. Acid secretion stimulated by carbachol and A23187 (to mimic elevations in intracellular calcium) was assessed by 14C aminopyrine uptake in response to IL-1beta, PKC, and sphingomyelinase manipulation.

RESULTS

IL-1beta inhibited carbachol and A23187 stimulated acid secretion in a dose dependent manner. The inhibitory actions were completely reversed by each of three different PKC inhibitors, staurosporine, H-7, and chelerythrine, as well as by PKC depletion with high dose phorbol ester pretreatment. IL-1beta did not downregulate parietal cell muscarinic receptor. IL-1beta significantly increased membrane PKC activity. Activation of the sphingomyelinase/ceramide pathway had no effect on basal or stimulated acid secretion. The inhibitory action of IL-1beta was independent of protein kinase A and protein kinase G activity.

CONCLUSIONS

IL-1beta directly inhibits parietal cell carbachol stimulated acid secretion. This action occurs distal to muscarinic receptor activation and elevations in intracellular calcium and requires PKC.

RGS2 blocks slow muscarinic inhibition of N-type Ca(2+) channels reconstituted in a human cell line

1. Native N-type Ca(2+) channels undergo sustained inhibition through a slowly activating pathway linked to M1 muscarinic acetylcholine receptors and Galphaq/11 proteins. Little is known concerning the regulation of this slow inhibitory pathway. We have reconstituted slow muscarinic inhibition of N-type channels in HEK293 cells (a human embryonic kidney cell line) by coexpressing cloned alpha1B (Ca(V)2.2) Ca(2+) channel subunits and M1 receptors. Expressed Ca(2+) currents were recorded using standard whole-cell, ruptured-patch techniques. 2. Rapid application of carbachol produced two kinetically distinct components of Ca(2+) channel inhibition. The fast component of inhibition had a time constant of < 1 s, whereas the slow component had a time constant of 5-40 s. Neither component of inhibition was reduced by pertussis toxin (PTX) or staurosporine. 3. The fast component of inhibition was selectively blocked by the Gbetagamma-binding region of beta-adrenergic receptor kinase 1, suggesting that fast inhibition is mediated by Gbetagamma released from Galphaq/11. 4. The slow component of inhibition was selectively blocked by regulator of G protein signalling 2 (RGS2), which preferentially interacts with Galphaq/11 proteins. RGS2 also attenuated channel inhibition produced by intracellular dialysis with non-hydrolysable GTPgammaS. Together these results suggest that RGS2 selectively blocked slow inhibition by functioning as an effector antagonist, rather than as a GTPase-accelerating protein (GAP). 5. These experiments demonstrate that slow muscarinic inhibition of N-type Ca(2+) channels can be reconstituted in non-neuronal cells, and that RGS2 can selectively block slow muscarinic inhibition while leaving fast muscarinic inhibition intact. These results identify RGS2 as a potential physiological regulator of the slow muscarinic pathway.

Low-affinity M(2) receptor binding state mediates mouse atrial bradycardia: comparative effects of carbamylcholine and the M(1) receptor agonists sabcomeline and xanomeline

Carbamylcholine, a nonselective muscarinic receptor agonist, and sabcomeline and xanomeline, functional M(1) receptor-selective agonists with high M(2) receptor affinities, were used to explore the relationship of the M(2) receptor affinity of these agonists to mouse atrial bradycardia and to understand the relationship of the high and low M(2) receptor affinity states to carbamylcholine-induced mouse atrial bradycardia. All three agonists produced bradycardia with sabcomeline (pEC(50) = 6.7) more potent than either carbamylcholine (pEC(50) = 5.9) or xanomeline (pEC(50) = 5.1). Sabcomeline and carbamylcholine produced a rapid, concentration-related bradycardia, which was antagonized by atropine with pK(B) values of 8.6 and 8.9, respectively. In addition, sabcomeline antagonized carbamylcholine-induced bradycardia (pK(B) = 7.48), indicating that sabcomeline was a partial agonist at M(2) receptors. In contrast, xanomeline (up to 10(-5) M), did not antagonize carbamylcholine-induced bradycardia, and atropine (3.0 x 10(-8) M) did not antagonize xanomeline-induced bradycardia, suggesting that xanomeline-induced bradycardia was not mediated by M(2) receptors. Analysis of receptor occupancy curves indicated that bradycardia resulted from the interaction of carbamylcholine with the low- rather than high-affinity state of the M(2) receptor and that sabcomeline was a partial agonist at M(2) receptors in mouse atria. In contrast, similar analysis for xanomeline using the receptor affinity of xanomeline at M(2) receptors (1.8 x 10(-8) M) was not consistent with classical receptor theory. These data document that 1) the low-affinity state of the M(2) receptor is responsible for muscarinic-induced atrial bradycardia, 2) sabcomeline was an M(2) receptor partial agonist, and 3) xanomeline-induced bradycardia was not mediated by activation of M(2) muscarinic receptors.

Synthesis and neuromuscular blocking activity of 16beta-piperidinosteroidal derivatives

The synthesis and pharmacological profiles of some new steroidal mono- and bisquaternary ammonium derivatives have been described. The compounds featured have been conceptually derived structurally from two lead structures: pancuronium bromide 1 and chandonium iodide 2. In vitro and in vivo neuromuscular blocking studies have indicated the monoquaternary compound 15 to be less active than the bisquaternary compounds 10 and 11. The compound 11 has been found to be more active than d-tubocurarine.

A pharmacological examination of venoms from three species of death adder (Acanthophis antarcticus, Acanthophis praelongus and Acanthophis pyrrhus)

The common (A. antarcticus), northern (A. praelongus) and desert (A. pyrrhus) death adders are species belonging to the Acanthophis genus. The present study compared some pharmacological aspects of the venoms of these species and examined the in vitro efficacy of death adder antivenom. Neurotoxicity was determined by the time to produce 90% inhibition (t(90)) of indirect (0.1 Hz, 0.2 ms, supramaximal voltage) twitches in the chick biventer cervicis nerve-muscle (3-10 microg/ml) and mouse phrenic nerve-diaphragm (10 microg/ml) preparations. A. praelongus venom was significantly less neurotoxic than A. antarcticus venom but was not significantly different from A. pyrrhus venom. In the biventer muscle, all three venoms (3-10 microg/ml) abolished responses to exogenous ACh (1 mM) and carbachol (20 microM), but not KCl (40 mM), indicating activity at post-synaptic nicotinic receptors. All venoms (30 microg/ml) failed to produce significant inhibition of direct twitches (0.1 Hz, 2.0 ms, supramaximal voltage) in the chick biventer cervicis nerve-muscle preparation. However, A. praelongus (30 microg/ml) venom initiated a significant direct contracture of muscle, indicative of some myotoxic activity. The prior (10 min) administration of death adder antivenom (1 unit/ml), which is raised against A. antarcticus venom, markedly attenuated the twitch blockade produced by all venoms (10 microg/ml). Administration of antivenom (1.5 units/ml) at t(90) markedly reversed, over a period of 4 h, the inhibition of twitches produced by A. praelongus (3 microg/ml, 72+/-6% recovery) and A. pyrrhus (3 microg/ml, 51+/-9% recovery) but was less effective against A. antarcticus venom (3 microg/ml, 22+/-7% recovery). These results suggest that all three venoms contain postsynaptic neurotoxins. Death adder antivenom displayed differing efficacy against the in vitro neurotoxicity of the three venoms.

Thymoquinone-induced relaxation of guinea-pig isolated trachea

The effect of thymoquinone (TQ), the main constituent of the volatile oil of black seed (Nigella sativa), on the guinea-pig isolated tracheal zig-zag preparation was investigated. TQ caused a concentration-dependent decrease in the tension of the tracheal smooth muscle precontracted by carbachol. The effects of TQ were significantly potentiated by pretreatment of the tracheal preparations with quinacrine, a phospholipase A2 inhibitor, nordihydroguiaretic acid, a lipoxygenase inhibitor and by pretreatment with methylene blue, an inhibitor of soluble guanylyl cyclase. On the other hand, the effects of TQ were not influenced by pretreatment of the tracheal preparations with indomethacin, a cyclooxygenase inhibitor, propranolol, a non-selective beta-adrenoceptor blocker or by the pretreatment with theophylline, an adenosine receptors antagonist TQ totally abolished the pressor effects of histamine and serotonin on the guinea-pig isolated tracheal and ileum smooth muscles. The results of the present study suggest that TQ induced relaxation of precontracted tracheal preparation is probably mediated, at least in part, by inhibition of lipoxygenase products of arachidonic acid metabolism and possibly by non-selective blocking of the histamine and serotonin receptors. This relaxant effect of TQ, further support the traditional use of black seeds either alone or in combination with honey to treat bronchial asthma.

A flowcytometric method for evaluation of acid secretion from isolated rat gastric mucosal cells

Studies on the gastric proton pump are mostly performed on the H(+), K(+)-ATPase enzyme in the microsomal preparation or by aminopyrine accumulation in the gastric parietal cells. H(+), K(+)-ATPase activity is estimated by both spectrophotometric and fluorimetric methods. In the present study, quenching or augmentation in acridine orange (AO) fluorescence was monitored on a flowcytometer in rat gastric mucosal cells. Rat gastric mucosal cells were isolated by the standard pronase--EDTA method. The effect of oleic acid, a proton pump inhibitory was evaluated on gastric parietal cell activity and was compared with its effect on proton transport, H(+), K(+)-ATPase, and p-nitrophenyl phosphatase (p-NPPase) activity in gastric microsomes. In addition, the effect of histamine and carbachol, gastric acid release inducers, was also investigated by flowcytometry in isolated parietal cells. Histamine and carbachol, in a dose-dependent manner, stimulated acid release from isolated gastric cells. Oleic acid also dose-dependently inhibited the basal and stimulated acid release from the cells, as well as in all three enzyme preparations associated with gastric proton pump activity. Thus, the results suggest that flowcytometric method might be used to study basal, as well as stimulated, proton pump activity in isolated gastric parietal cells.

The lack of compound 48/80-induced contraction in isolated trachea of mast cell-deficient Ws/Ws rats in vitro: the role of connective tissue mast cells

In the rat trachea, two types of mast cells have been identified, connective tissue mast cells and mucosal mast cells. Their different characteristics may account for their different biological functions. The role of connective tissue mast cells in tracheal contraction as one feature of the immediate reaction of asthma was studied in vitro in isolated trachea, using tissue derived from mast cell-deficient (Ws/Ws) rats, heterozygous (Ws/+) rats and control (+/+) rats, and compound 48/80 as a potent inducer of mast cell degranulation. The contractile response of tracheas from the three types of rats was also studied upon exposure to the following spasmogens: histamine, 5-hydroxytryptamine (5-HT), and carbachol. Histamine content in tissues reflected the differing mast cell numbers in strips from the three rat types. It was found that carbachol and 5-HT elicited tracheal contraction in a similar manner in strips from the three types of rats. Histamine had no contractile effect. Compound 48/80, at a dose of 25 microg/ml, elicited contraction in tracheas from both control (+/+) and heterozygous (Ws/+), but not in trachea from Ws/Ws rats. Compound 48/80-induced contractions in tracheas from +/+ rats were inhibited by 0.1 microM ketanserin and 0.1 microM nedocromil, but not by 0.1 microM mepyramine. Enzyme histochemistry confirmed that the degranulation occurred in connective tissue mast cells, but not in mucosal mast cells. We concluded that connective tissue mast cells play an important role in rat tracheal contraction via 5-HT release induced by compound 48/80. In addition, the specific mast cell-deficient (Ws/Ws) rats provide a good tool for studying the roles of mast cells in airway system.

Halothane and isoflurane augment depolarization-induced cytosolic CA2+ transients and attenuate carbachol-stimulated CA2+ transients

BACKGROUND

Neuronal excitability is in part determined by Ca2+ availability that is controlled by regulatory mechanisms of cytosolic Ca2+ ([Ca2+]cyt). Alteration of any of those mechanisms by volatile anesthetics (VAs) may lead to a change in presynaptic transmission and postsynaptic excitability. Using a human neuroblastoma cell line, the effects of halothane and isoflurane on cytosolic Ca2+ concentration ([Ca2+]cyt) in response to K+ and carbachol stimulation were investigated.

METHODS

Volatile anesthetic (0.05-1 mm) action on stimulated [Ca2+]cyt transients were monitored in suspensions of SH-SY5Y cells loaded with fura-2. Potassium chloride (KCl; 100 mm) was used to depolarize and activate Ca2+ entry through voltage-dependent calcium channels; 1 mm carbachol was used to activate muscarinic receptor-mediated inositol triphosphate (IP3)-dependent intracellular Ca2+ release. Sequential stimulations, KCl followed by carbachol and vice versa, were used to investigate interactions between intracellular Ca2+ stores.

RESULTS

Halothane and isoflurane in clinically relevant concentrations enhanced the K+-evoked [Ca2+]cyt transient whether intracellular Ca2+ stores were full or partially depleted. In contrast, halothane and isoflurane reduced the carbachol-evoked [Ca2+]cyt transient when the intracellular Ca2+ stores were full but had no effect when the Ca2+ stores were partially depleted by KCl stimulation.

CONCLUSIONS

Volatile anesthetics acted on sites that differently affect the K+- and carbachol-evoked [Ca2+]cyt transients. These data suggest the involvement of an intracellular Ca2+ translocation from the caffeine-sensitive Ca2+ store to the inositol triphosphate-sensitive Ca2+ store that was altered by halothane and isoflurane.