Human esophageal smooth muscle cells express muscarinic receptor subtypes M(1) through M(5)

Breast cancer: Muscarinic receptors as new targets for tumor therapy

The development of breast cancer is a complex process that involves the participation of different factors. Several authors have demonstrated the overexpression of muscarinic acetylcholine receptors (mAChRs) in different tumor tissues and their role in the modulation of tumor biology, positioning them as therapeutic targets in cancer. The conventional treatment for breast cancer involves surgery, radiotherapy, and/or chemotherapy. The latter presents disadvantages such as limited specificity, the appearance of resistance to treatment and other side effects. To prevent these side effects, several schedules of drug administration, like metronomic therapy, have been developed. Metronomic therapy is a type of chemotherapy in which one or more drugs are administered at low concentrations repetitively. Recently, two chemotherapeutic agents usually used to treat breast cancer have been considered able to activate mAChRs. The combination of low concentrations of these chemotherapeutic agents with muscarinic agonists could be a useful option to be applied in breast cancer treatment, since this combination not only reduces tumor cell survival without affecting normal cells, but also decreases pathological neo-angiogenesis, the expression of drug extrusion proteins and the cancer stem cell fraction. In this review, we focus on the previous evidences that have positioned mAChRs as relevant therapeutic targets in breast cancer and analyze the effects of administering muscarinic agonists in combination with conventional chemotherapeutic agents in a metronomic schedule.

Clozapine-induced dysphagia with secondary substantial weight loss

Dysphagia is listed as a 'rare' side effect following clozapine treatment. In this case report, we describe how significant clozapine-induced dysphagia has led to significant reduction of nutritional intake with subsequent substantial weight loss. An 18-year-old single man with an established diagnosis of treatment-resistant paranoid schizophrenia recovered well on a therapeutic dose of clozapine. However, he was noted to lose weight significantly (up to 20% of his original weight) as the dose was uptitrated. This was brought about by development of dysphagia, likely to be due to clozapine. Addition of nutritional supplementary liquids and initiation of a modified behavioural dietary/swallowing programme, while repeatedly mastering the Mendelsohn manoeuvre technique, alleviated the swallowing difficulties and restored his weight.

Estrogen and G protein-coupled estrogen receptor agonist G-1 cause relaxation of human gallbladder

OBJECTIVE

Estrogen interacts with a membrane receptor, G protein-coupled estrogen receptor (GPER). It was reported that 17β-estradiol was able to inhibit contraction of the human colon and cause relaxation of the guinea pig gallbladder, however, the involvement of GPER was not clarified. The aim of the present study was to investigate the effect of estrogen on human gallbladder motility and the possible role of GPER.

MATERIALS AND METHODS

Relaxation of human gallbladder strips were measured using isometric transducers. Expression of GPER was evaluated by reverse transcription polymerase chain reaction (PCR), realtime PCR, and immunohistochemistry.

RESULTS

In human gallbladder strips, 17β-estradiol and G-1 elicited marked and rapid relaxation, whereas tamoxifen produced mild concentration-dependent relaxation. The relative efficacies to cause relaxation were as follows: 17β-estradiol = G-1 > tamoxifen. The relaxant response of 17β-estradiol was not attenuated by tetrodotoxin or conotoxin GVIA. This implies that nerve stimulation was not involved in the 17β-estradiol-induced gallbladder relaxation. Analysis by reverse transcription PCR and real-time PCR showed that GPER was expressed in the human gallbladder. Further analysis by immunohisto-chemistry revealed that GPER was expressed in the gallbladder muscle. This suggests that 17β-estradiol relaxes the human gallbladder via GPER.

CONCLUSION

These results demonstrate for the first time that 17β-estradiol and GPER agonist G-1 cause relaxation of the human gallbladder, probably through GPER. Estrogen might play an important role in the control of human gallbladder motility.

Acetylcholine-induced AMP-activated protein kinase activation attenuates vasoconstriction through an LKB1-dependent mechanism in rat aorta

Numerous studies of acetylcholine (ACh)-induced endothelium-dependent relaxation in arteries have been reported since the original description by Furchgott and Zawadzki (1980). ACh also produces endothelium-independent relaxation. However, it is still unknown whether ACh-induced AMP-activated protein kinase (AMPK) activation can attenuate vasoconstriction in endothelium-denuded rat aorta. Here, we investigated whether ACh may exert a regulatory effect for vascular tone via AMPK activation and its underlying mechanism in vascular smooth muscle cells (VSMCs). Western blotting showed that ACh dose- and time-dependently increased LKB1 and AMPK phosphorylation in VSMCs. The ACh-induced activation of AMPK required muscarinic receptors in VSMCs. LKB1 and AMPK activation by ACh inhibited myosin light-chain kinase (MLCK) and phosphorylated myosin light chain (p-MLC) expression in VSMCs. In addition, a tension study showed the inhibitory effect of ACh-induced AMPK activation on phenylephrine-mediated contraction in endothelium-denuded rat aorta. These data suggest that the ACh-induced activation of AMPK may attenuate vasoconstriction via LKB1-AMPK-dependent mechanism in endothelium-denuded rat aorta.

Muscarinic receptor M3 mediates human gallbladder contraction through voltage-gated Ca2+ channels and Rho kinase

OBJECTIVE

Muscarinic receptors mediate contraction of the human gallbladder through unclear receptor subtypes. The aim of the present study was to characterize muscarinic acetylcholine receptors mediating contraction of the human gallbladder.

MATERIALS AND METHODS

Contraction of human gallbladder muscle strips caused by agonists carbachol and muscarine was measured and the inhibition of carbachol-induced contraction by muscarinic receptor antagonists was evaluated. Reverse transcription polymerase chain reaction was performed to determine the existence of muscarinic receptor subtypes.

RESULTS

Carbachol and muscarine caused concentration-dependent contraction of gallbladder strips. Four receptor antagonists, including atropine, 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP), methoctramine, and pirenzepine, inhibited the carbachol-induced contraction. The relative inhibitory potency of these receptor antagonists was atropine > 4-DAMP > methoctramine > pirenzepine. The antagonist affinity estimates (pA(2) values) correlated with the known affinities at M(3), M(4), and M(5) muscarinic receptors. In addition, the M(4)-selective antagonist muscarinic toxin 3 did not inhibit and the M(5)-selective positive allosteric modulator VU0238429 did not potentiate carbachol-induced gallbladder contraction. This suggests that M(3) muscarinic receptors mediate the muscarinic response predominantly. The contractile response of carbachol was attenuated by the voltage-gated Ca(2+) channel inhibitor nifedipine and Rho-kinase inhibitor H-1152, but not affected by protein kinase C inhibitor chelerythrine. This implies the involvement of voltage-gated Ca(2+) channel and Rho kinase but not protein kinase C.

CONCLUSIONS

These results suggest a major role of M(3) muscarinic receptors mediating the human gallbladder contraction through voltage-gated Ca(2+) channels and Rho kinase. M(3)-selective muscarinic receptor antagonists could be of therapeutic importance in the treatment of biliary motility disorders.

In vitro effect of bethanechol and suberyldicholine on regions of guinea pig esophagus

BACKGROUND

Tissue engineering and regenerative medicine is envisaged as the future option for esophageal replacement; however, engineering of a functional esophagus is impeded by the limited understanding of the anatomical complexity of this dynamic muscular organ. The aim of this study was to characterize the function of native esophageal tissue and determine differences in functional response to stimulation between anatomical sites.

MATERIALS AND METHODS

The in-vitro response of guinea pig esophageal preparations, from various anatomical sites, to muscle agonists was investigated. Esophageal strips were exposed to bethanechol, an agonist of muscarinic receptors located on smooth muscle, and suberyldicholine, an agonist of nicotinic receptors located on striated muscle, within a Schuler organ bath, to determine the contractile response on the various segments of the esophagus.

RESULTS

The esophagus responded in a reliable and consistent manner to agonist stimulation. Bethanechol dose response curves were constructed with doses of 10 to 300 μM. The average maximal contractions to bethanechol exposure were 4.51, 4.80, 5.55, and 9.15 mN for upper, upper middle, lower middle, and lower esophageal segments, respectively. Responses to singular stimulation with 30 μM suberyldicholine in the presence of tetrodotoxin (100 μM) gave average contractions of 1.07, 0.84, 2.60, and 3.02 mN for upper, upper middle, lower middle, and lower esophageal segments, respectively. Bethanechol and suberyldicholine-induced responses were greater in the lower esophagus in comparison to the upper esophageal segments.

CONCLUSION

These findings pave the way for the use of an in-vitro bethanechol and suberyldicholine-induced contraction model for future assessment of engineered esophageal tissue.

Muscarinic agonists and antagonists: effects on gastrointestinal function

Muscarinic agonists and antagonists are used to treat a handful of gastrointestinal (GI) conditions associated with impaired salivary secretion or altered motility of GI smooth muscle. With regard to exocrine secretion, the major muscarinic receptor expressed in salivary, gastric, and pancreatic glands is the M₃ with a small contribution of the M₁ receptor. In GI smooth muscle, the major muscarinic receptors expressed are the M₂ and M₃ with the M₂ outnumbering the M₃ by a ratio of at least four to one. The antagonism of both smooth muscle contraction and exocrine secretion is usually consistent with an M₃ receptor mechanism despite the major presence of the M₂ receptor in smooth muscle. These results are consistent with the conditional role of the M₂ receptor in smooth muscle. That is, the contractile role of the M₂ receptor depends on that of the M₃ so that antagonism of the M₃ receptor eliminates the response of the M₂. The physiological roles of muscarinic receptors in the GI tract are consistent with their known signaling mechanisms. Some so-called tissue-selective M₃ antagonists may owe their selectivity to a highly potent interaction with a nonmuscarinic receptor target.

Effects of acetylcholine on sling and clasp fibers of the human lower esophageal sphincter

BACKGROUND AND AIM

  Manometric studies on the human lower esophageal sphincter (LES) have shown radial asymmetry of the high-pressure zone (HPZ). The aim of this study was to compare the functional properties of human LES clasp and sling muscles, and to look at their relationship with the expression of muscarinic receptors and intracellular Ca(2+) concentration.

METHODS

  Muscle strips of sling and clasp fibers from the LES were obtained from patients undergoing subtotal esophagectomy. Isometric tension responses of the strips to acetylcholine were studied. Western blotting and reverse transcription-polymerase chain reaction (RT-PCR) were used to determine the expression of five subtypes of muscarinic receptors. Intracellular Ca(2+) ([Ca(2+) ]i) was measured using laser scanning confocal microscopy.

RESULTS

  Acetylcholine caused a concentration-dependent increase in the tension of sling and clasp strips, the sling strip being stronger than clasp (P=0.00). Messenger RNA and protein for the five muscarinic acetylcholine receptor (mAChRs) expressed in the sling and clasp muscles were highest for M2, and then in decreasing levels: M(3)>M(1)>M(4)>M(5) . Acetylcholine caused significant elevation of [Ca(2+) ]i in sling and clasp muscle cells in the presence of extracellular Ca2+ (1.5mmol/L), and Ach-induced [Ca(2+) ]i elevation was 1.6 times greater in sling cells than in clasp cells.

CONCLUSION

  Variation of intracellular concentrations of Ca(2+) may be the reason for differential responses to acetylcholine for sling versus clasp fibers. However, these differences are not associated with the distribution and the level of expression of the five mAChRs between the two muscle types. Further study should focus on the ligand affinity and signal transduction pathway.

A nocturnal decline of salivary pH associated with airway hyperresponsiveness in asthma

Salivary pH is associated with esophageal acid reflux and neutralization of esophageal acid. In this study, we assessed the association between nocturnal decline of salivary pH and airway hyperresponsiveness. Salivary pH was serially assessed in 9 patients with mild asthma (7 men and 2 women; mean age 33.3 years; mean %predicted FEV(1.0) 89.4%) and 10 healthy volunteers (6 men and 4 women; mean age 31.2 years) using a pH indicator tape. The buffering capacity of saliva was defined as the median effective dose (ED(50)) for acidification of saliva with 0.01 N HCl, and airway responsiveness was defined as the dose of methacholine producing a 35% fall in Grs (PD(35)-Grs). There was a significant correlation between the values obtained from the pH indicator tape and those obtained from the electrometric pH meter. Using the indicator tape for sequential monitoring, we observed a nocturnal fall (ΔpH) in salivary pH in all subjects. A significant correlation was found between airway hyperresponsiveness (PD(35)-Grs) and either ΔpH or ED(50) in mildly asthmatic patients. Vagal reflux dysfunction might contribute to nocturnal salivary pH as well as to airway hyperresponsiveness in mild asthmatics.

Fabrication and in vitro and in vivo cell infiltration study of a bilayered cryogenic electrospun poly(D,L-lactide) scaffold

Cryogenic electrospinning has previously been demonstrated for controlling the pore sizes of electrospun scaffolds, which has been impossible with traditional electrospinning processes. This article describes the application of the cryogenic technique to fabricate a bilayered electrospun poly(D,L-lactide) scaffold (BLES) in a single uninterrupted process. The resulting BLES consisted of a traditional electrospun (ES) fibrous layer with a dense pore area of 17 +/- 3 microm(2) adjacent to a cryogenic electrospun layer (CES) with a pore area of 3300 +/- 500 microm(2). The significance of this bilayered scaffold was to mimic the anatomical structure of tissues with dense basement membrane followed by loose and highly porous connective tissue such as skin and blood vessels. Cell infiltration in the BLES was compared in vitro and in vivo. Both studies suggested the CES supported high cell infiltration, whereas the ES could serve as a physical barrier to prevent cell infiltration across the CES-ES boundary because of its size exclusion. The bilayered structure produced by this technique suggests a great potential for engineering tissues with similar architectures.

P2X and P2Y Receptors Mediate Contraction Induced by Electrical Field Stimulation in Feline Esophageal Smooth Muscle

It is well-known that electrical field stimulation (EFS)-induced contraction is mediated by a cholinergic mechanism and other neurotransmitters. NO, ATP, calcitonin gene-related peptide (CGRP), and substance P are released by EFS. To investigate the purinergic mechanism involved in the EFS-induced contraction, purinegic receptors antagonists were used. Suramine, a non-selective P2 receptor antagonist, reduced the contraction induced by EFS. NF023 (10(-7)~10(-4) M), a selective P2X antagonist, inhibited the contraction evoked by EFS. Reactive blue (10(-6)~10(-4) M), selective P2Y antagonist, also blocked the contraction in a dose-dependent manner. In addition, P2X agonist α,β-methylene 5'-adenosine triphosphate (αβMeATP, 10(-7)~10(-5) M) potentiated EFS-induced contraction in a dose-dependent manner. P2Y agonist adenosine 5'-[β-thio]diphosphate trilithium salt (ADPβS, 10(-7)~10(-5) M) also potentiated EFS-induced contractions in a dose-dependent manner. Ecto-ATPase activator apyrase (5 and 10 U/ml) reduced EFS-induced contractions. Inversely, 6-N,N-diethyl-D-β,γ-dibromomethylene 5'-triphosphate triammonium (ARL 67156, 10(-4) M) increased EFS-induced contraction. These data suggest that endogenous ATP plays a role in EFS-induced contractions which are mediated through both P2X-receptors and P2Y-receptors stimulation in cat esophageal smooth muscle.

Muscarinic acetylcholine receptors present in human osteoblast and bone tissue

Acetylcholine is the predominant neurotransmitter in the neuromuscular junction, and a role in bone has been postulated. The expression of nicotinic receptors has been reported in osteoblasts, but the expression and function of muscarinic receptor in bone remain obscure. In this study, we investigated the expression and functional activities of muscarinic receptor subtypes in human osteoblast cell lines and animal and human bone tissue. The mRNA levels of muscarinic receptor subtypes were detected by reverse-transcription polymerase chain reaction. We found that muscarinic subtypes m1, m2, m3, m4, and m5 were expressed at different levels in human osteosarcoma HOS cells, rat femur, and human rib bone tissue; m1, m4, m5 were in cultured mouse femur bone cells and cultured mouse calvarial bone cells; m2, m3, m4 were in bovine bone. The mRNA of neuronal markers, light-, medium- and heavy-neurofilament, was not found in human bone tissues to exclude the possible contamination from neuronal tissue. Methacholine induced an elevation in cytosolic calcium concentration and proliferation in HOS cells. Both effects were blocked by atropine. We conclude that muscarinic receptor is present in bone tissue to evoke calcium signaling and modulate cell proliferation. Different muscarinic receptor subtypes are distributed in various parts of the animal skeletal system including the different species and bone portions. Bone remodeling involving osteoblast proliferation leads the possibilities that muscarinic receptor may play roles in bone remodeling.

Regulation of M2, M3, and M4 muscarinic receptor expression in K562 chronic myelogenous leukemic cells by carbachol

CONTEXT

Muscarinic receptors mediate a variety of cellular responses to acetylcholine, including inhibition of adenylate cyclase, breakdown of phosphoinositide and modulation of ion channels. These receptors are relatively abundant in the central nervous system and peripheral parasympathetic nervous system. Many cells express a mixture of muscarinic receptor transcripts. Changes in muscarinic M(2) and M(3) receptor mRNA levels in response to agonist treatment have been reported in cerebellar granule cells, Chinese hamster ovary cells, lymphocytes and in the human neuroblastoma cell line SH-SY5Y.

OBJECTIVE

In this study, we investigated the effects of agonist stimulation on cell proliferation and on the levels of muscarinic receptor expression in K562 chronic myelogenous leukemia cells.

METHODS

Total RNA and crude membrane fractions were prepared from K562 cells challenged with carbachol (CCh). Muscarinic receptor subtype expression was determined by RT-PCR and western blot analysis. Proliferation and cell viability were evaluated by the trypan blue exclusion test and BrDU labeling.

RESULTS

We showed that CCh-treatment leads to changes in muscarinic M(2), M(3), and M(4) receptor transcripts as well as M(2) and M(3) protein levels. We also found that CCh decreased proliferation of K562 cells in a time dependent manner, an effect prevented by atropine. These results suggest that CCh modulates K562 chronic myelogenous leukemic cells proliferation through muscarinic acetylcholine receptors.

M2, M3, and M4 muscarinic receptors are expressed in the guinea pig gallbladder

AIM

The identity of muscarinic acetylcholine receptors (mAchR) involved in cholinergic-mediated contraction of the guinea pig gallbladder has been a matter of debate. Different groups have suggested the involvement of M(1), M(2), M(3), or M(4) receptor subtypes in the contraction of this tissue. The objective of this study was to identify the mAchR subtypes expressed in the guinea pig gallbladder by RT-PCR.

METHODS

Total RNA prepared from frozen guinea pig gallbladder tissue was amplified by using specific primers for the M(1)-M(4) receptor subtypes.

RESULTS

M(2), M(3), and M(4) transcripts were detected in the following rank order: M(4) > M(2) > M(3). We were unable to demonstrate the expression of the M(1) receptor subtype in this tissue.

CONCLUSIONS

Our results are in agreement with our previous binding and functional data.

Dependence of alignment direction on magnitude of strain in esophageal smooth muscle cells

The response of cells in vitro to mechanical forces has been the subject of much research using devices to exert controlled mechanical stimulation on cultured cells or isolated tissue. In this study, esophageal smooth muscle cells were seeded on flexible polyurethane membranes to form a confluent cell layer. The cells were then subjected to uniform cyclic stretch of varying magnitudes at a frequency of approximately five cycles per minute in a custom made mechatronic bioreactor, providing similar strains experienced in the in vivo mechanical environment of the esophagus. The results show that the orientation response is dependent on the magnitude of cyclic stretch applied. Smooth muscle cells showed parallel alignment to the force direction at low cyclic strains (2%) compared to the hill-valley morphology of static controls. At higher strains (5% and 10% magnitude), the cells exhibited a consistent alignment perpendicular to the strain. To our knowledge, this is the first time that the alignment direction's dependence on strain magnitude has been demonstrated. MTS analysis indicated that cell metabolism was reduced when mechanical strain was applied, and proliferation was inhibited by mechanical strain. Protein expression indicates a decrease in smooth muscle alpha-actin, indicative of changes in cell phenotype, an increase in vimentin, which is associated with increased cell motility, and an increase in desmin, indicating differentiation in stimulated cells.

Calcium sensitization in human esophageal muscle: role for RhoA kinase in maintenance of lower esophageal sphincter tone

A rise in intracellular-free calcium ([Ca(2+)](i)) concentration is important for initiating contraction of smooth muscles, and Ca(2+) sensitization involving RhoA kinase can sustain tension. We previously found that [Ca(2+)](i) was comparable in cells from the esophageal body (EB) and lower esophageal sphincter (LES) muscles, despite the fact that the LES maintains resting tone. We hypothesized that Ca(2+) sensitization contributes to contraction in human esophageal muscle. Tension and [Ca(2+)](i) were measured simultaneously in intact human EB and LES muscles using the ratiometric Ca(2+)-sensitive dye fura-2. Spontaneous oscillations in EB muscle tension were associated with transient elevations of [Ca(2+)](i). Carbachol caused a large increase in tension, compared with spontaneous oscillations, although the rise of [Ca(2+)](i) was similar, suggesting Ca(2+) sensitization. The RhoA-kinase blockers (R)-(+)-trans-4-(1-aminoethyl)-N-(4-pyridyl) cyclohexanecarboxamide dihydrochloride monohydrate (Y-27632) and 1-(5-isoquinolinesulfonyl)-homopiperazine hydrochloride (HA-1077) reduced carbachol- and nerve-evoked contraction of the EB, accompanied by smaller reduction in the rise of [Ca(2+)](i). Protein kinase C inhibitors reduced force to a lesser extent. RhoA-kinase blockers caused concentration-dependent reduction of tension in spontaneously contracted LES muscles. Moreover, RhoA-kinase blockers reduced intrinsic nerve-evoked and carbachol-evoked contraction. However, there was no effect on nerve- or nitric oxide-mediated relaxation of LES. Ca(2+) sensitization mediated by the RhoA-kinase pathway has an important role in contraction of human EB muscles and LES tonic contraction, a feature not previously recognized.

Immunohistochemical localisation of cholinergic muscarinic receptor subtype 1 (M1r) in the guinea pig and human enteric nervous system

Little is known regarding the location of cholinergic muscarinic receptor 1 (M1r) in the ENS, even though physiological data suggest that M1rs are central to cholinergic neurotransmission. This study localised M1rs in the ENS of the guinea pig ileum and human colon using fluorescence immunohistochemistry and RT-PCR in human colon. Double labelling using antibodies against neurochemical markers was used to identify neuron subytpes bearing M1r. M1r immunoreactivity (IR) was present on neurons in the myenteric and submucosal ganglia. The two antibodies gave similar M1r-IR patterns and M1r-IR was abolished upon antibody preabsorption. M1r-IR was present on cholinergic and nNOS-IR nerve cell bodies in both guinea pig and human myenteric neurons. Presynaptic M1r-IR was present on NOS-IR and VAChT-IR nerve fibres in the circular muscle in the human colon. In the submucosal ganglia, M1r-IR was present on a population of neurons that contained cChAT-IR, but did not contain NPY-IR or calretinin-IR. M1r-IR was present on endothelial cells of blood vessels in the submucosal plexus. The localisation of M1r-IR in the guinea pig and human ENS shown in this study agrees with physiological studies. M1r-IR in cholinergic and nitrergic neurons and nerve fibres indicate that M1rs have a role in both cholinergic and nitrergic transmission. M1r-IR present in submucosal neurons suggests a role in mediating acetylcholine's effect on submucosal sensory and secretomotor/vasodilator neurons. M1r-IR present on blood vessel endothelial cells suggests that M1rs may also mediate acetylcholine's direct effect on vasoactivation.

Distribution of muscarinic receptor subtypes and interstitial cells of Cajal in the gastrointestinal tract of healthy dairy cows

OBJECTIVE

To describe the distribution of muscarinic receptor subtypes M(1) to M(5) and interstitial cells of Cajal (ICCs) in the gastrointestinal tract of healthy dairy cows.

SAMPLE POPULATION

Full-thickness samples were collected from the fundus, corpus, and pyloric part of the abomasum and from the duodenum, ileum, cecum, proximal loop of the ascending colon, and both external loops of the spiral colon of 5 healthy dairy cows after slaughter.

PROCEDURES

Samples were fixed in paraformaldehyde and embedded in paraffin. Muscarinic receptor subtypes and ICCs were identified by immunohistochemical analysis.

RESULTS

Staining for M(1) receptors was found in the submucosal plexus and myenteric plexus. Antibodies against M(2) receptors stained nuclei of smooth muscle cells only. Evidence of M(3) receptors was found in the lamina propria, in intramuscular neuronal terminals, on intermuscular nerve fibers, and on myocytes of microvessels. There was no staining for M(4) receptors. Staining for M(5) receptors was evident in the myocytes of microvessels and in smooth muscle cells. The ICCs were detected in the myenteric plexus and within smooth muscle layers. Distribution among locations of the bovine gastrointestinal tract did not differ for muscarinic receptor subtypes or ICCs.

CONCLUSIONS AND CLINICAL RELEVANCE

The broad distribution of M(1), M(3), M(5), and ICCs in the bovine gastrointestinal tract indicated that these components are likely to play an important role in the regulation of gastrointestinal tract motility in healthy dairy cows. Muscarinic receptors and ICCs may be implicated in the pathogenesis of motility disorders, such as abomasal displacement and cecal dilatation-dislocation.

Kinetic and molecular evidences that human cardiac muscle express non-M2 muscarinic receptor subtypes that are able to interact themselves

In heart tissue five isoforms of the muscarinic acetylcholine receptor (mAChR) have been identified, designated m1-m5, of which only M1, M2 and M3 have functional evidences for their role in cardiac physiology. The present study was designed to explore the diversity of mAChR subtypes in human hearts and determine whether these subtypes are able to interact themselves. Expression of mRNAs encoding all five subtypes was readily detected by RT-PCR reaction in both atrial (A) and ventricle (V) samples. Immunoblotting, MABA and ELISA with subtype-specific antibodies confirmed the presence of M1, M2, M3, M4 and M5 proteins in membrane preparations from both A and V. Kinetic characterization using [(3)H]-QNB shown: (1) atrium had greater B(max) than did the ventricle, (2) [(3)H]-QNB behave as an allosteric modulator, inducing cooperativity at high and disclosing heterogeneity at low concentrations, (3) heterogenity was observed in pirenzepine, biperiden and tropicamide competition curves, being the high affinity sites compatible with M1 and M4 muscarinic receptor subtypes and (4) methoctramine competition curves in presence of selective muscarinic receptor subtypes antagonist displayed heterogeneity profile still maintaining cooperativity (n(H)>1), indicating muscarinic receptors subtypes are able to form homo- and hetero-oligomers. In conclusion, our results provide molecular and kinetic evidence for the presence of multiple subtypes of mAChR in human hearts, which are able to undergo discrete transitions from a non-cooperative kinetics of non-interacting monomers to a cooperative kinetics of interacting oligomers.

Functional and molecular analysis of L-type calcium channels in human esophagus and lower esophageal sphincter smooth muscle

Excitation of human esophageal smooth muscle involves the release of Ca(2+) from intracellular stores and influx. The lower esophageal sphincter (LES) shows the distinctive property of tonic contraction; however, the mechanisms by which this is maintained are incompletely understood. We examined Ca(2+) channels in human esophageal muscle and investigated their contribution to LES tone. Functional effects were examined with tension recordings, currents were recorded with patch-clamp electrophysiology, channel expression was explored by RT-PCR, and intracellular Ca(2+) concentration was monitored by fura-2 fluorescence. LES muscle strips developed tone that was abolished by the removal of extracellular Ca(2+) and reduced by the application of the L-type Ca(2+) channel blocker nifedipine (to 13 +/- 6% of control) but was unaffected by the inhibition of sarco(endo)plasmic reticulum Ca(2+)-ATPase by cyclopiazonic acid (CPA). Carbachol increased tension above basal tone, and this effect was attenuated by treatment with CPA and nifedipine. Voltage-dependent inward currents were studied using patch-clamp techniques and dissociated cells. Similar inward currents were observed in esophageal body (EB) and LES smooth muscle cells. The inward currents in both tissues were blocked by nifedipine, enhanced by Bay K8644, and transiently suppressed by acetylcholine. The molecular form of the Ca(2+) channel was explored using RT-PCR, and similar splice variant combinations of the pore-forming alpha(1C)-subunit were identified in EB and LES. This is the first characterization of Ca(2+) channels in human esophageal smooth muscle, and we establish that L-type Ca(2+) channels play a critical role in maintaining LES tone.

Regional differences in cholinergic regulation of potassium current in feline esophageal circular smooth muscle

Potassium channels are important contributors to membrane excitability in smooth muscles. There are regional differences in resting membrane potential and K(+)-channel density along the length of the feline circular smooth muscle esophagus. The aim of this study was to assess responses of K(+)-channel currents to cholinergic (ACh) stimulation along the length of the feline circular smooth muscle esophageal body. Perforated patch-clamp technique assessed K(+)-channel responses to ACh stimulation in isolated smooth muscle cells from the circular muscle layer of the esophageal body at 2 (distal)- and 4-cm (proximal) sites above the lower esophageal sphincter. Western immunoblots assessed ion channel and receptor expression. ACh stimulation produced a transient increase in outward current followed by inhibition of spontaneous transient outward currents. These ACh-induced currents were abolished by blockers of large-conductance Ca(2+)-dependent K(+) channels (BK(Ca)). Distal cells demonstrated a greater peak current density in outward current than cells from the proximal region and a longer-lasting outward current increase. These responses were abolished by atropine and the specific M(3) receptor antagonist 4-DAMP but not the M(1) receptor antagonist pirenzipine or the M(2) receptor antagonist methoctramine. BK(Ca) expression along the smooth muscle esophagus was similar, but M(3) receptor expression was greater in the distal region. Therefore, ACh can differentially activate a potassium channel (BK(Ca)) current along the smooth muscle esophagus. This activation probably occurs through release of intracellular calcium via an M(3) pathway and has the potential to modulate the timing and amplitude of peristaltic contraction along the esophagus.

Evidence for the involvement of neurotrophins in muscle transdifferentiation and acetylcholine receptor transformation in the esophagus ofMyf5−/−:MyoD−/−andNT-3−/−embryos

The primary aim of our study was to determine whether the esophageal innervation (i.e., vagal and enteric) and the skeletal muscle-secreted neurotrophins have a role in smooth-to-skeletal muscle transdifferentiation and in the muscarinic-to-nicotinic acetylcholine receptor type transition. To that end, we used genetically engineered embryos and immunohistochemistry. We found that, in the absence of Myf5 and MyoD, the esophageal muscle cells failed to develop the striated phenotype of acetylcholine receptors. In addition, the development of vagal and enteric innervation was delayed in Myf5(-/-):MyoD(-/-) and NT-3(-/-) mutants, but it was reestablished 2 days before the end of gestation. The smooth muscle cells in the esophagus appeared to be a distinct subpopulation of cells and their ability to transdifferentiate was based on their competence to express neurotrophins and their receptors. Finally, our data suggest a role for NT-3 in the esophageal muscle transdifferentiation.

Tetrodotoxin-sensitive Na+ channels and muscarinic and purinergic receptors identified in human erythroid progenitor cells and red blood cell ghosts

This article concerns the identification of different types of voltage-gated Na(+) channels and of muscarinic and purinergic receptors that are expressed in human erythroid precursor cells and red cell ghosts. We analyzed, by RT-PCR, RNA that was extracted from purified and synchronously growing human erythroid progenitor cells, differentiating from erythroblasts to reticulocytes in 7 to 14 days. These extracts were free of white cell and platelet contamination. Two types of voltage-gated, tetrodotoxin-sensitive Na(+) channels were found. These were Na(v)1.4 and Na(v)1.7, the former known to be present in skeletal muscle and the latter in peripheral nerve. By using a pan Na(+) channel antibody and Western blotting, an immunoreactive channel was detected in ghosts of human red blood cells, consistent with the expression of these two channels. The transcripts for four of the five known subtypes of muscarinic receptors were also identified, including subtypes M2, M3, M4, and M5, whereas subtype M1 was not found. Expression was also detected for the purinergic type receptors P2X(1), P2X(4), P2X(7), and P2Y(1) whereas types P2Y(2), P2Y(4), and P2Y(6) were not found. We also searched for but did not find transcripts for hBNP-1, a type 1b human brain sodium phosphate cotransporter, and cystic fibrosis transmembrane conductance regulator (CFTR). Implications regarding the presence of these different types of channels and receptors in human red blood cells and their functional significance are discussed.

Treatment of spastic esophageal motility disorders

Treatment of spastic motility disorders continues to be challenging. Therapeutic options remain limited due in part to our lack of understanding of the pathophysiology and significance of these disorders. Furthermore, most of therapeutic trials to date are hampered by the poorly designed nature of the study, including the small size of the trials and the lack of placebo arm. Most of the available information suggests that there seems to be an important dissociation between symptoms (chest pain/dysphagia) and esophageal dysmotility. Drug treatment aimed at visceral sensitivity seems more effective in relieving symptoms than spasmolytic medications. Recent trials with Botox, nitric oxide derivatives, and SSRIs offer promising results. Rigorous study design that includes large placebo-controlled trials is needed in this area.

Development of ovine fetal ileal motility: role of muscarinic receptor subtypes

OBJECTIVE

In the preterm human fetus, immaturity of gastrointestinal (GI) motility contributes to impairment of oral feeding and an increased risk of necrotizing enterocolitis. In view of the limited knowledge of fetal GI motility development, and the primary role of the muscarinic system in adult GI motility, we examined the development of GI muscarinic receptor subtypes associated with ileal motility.

STUDY DESIGN

Ovine term fetal, newborn, and pregnant adult ileal longitudinal muscle contractile responses to muscarinic agonists (bethanechol) and muscarinic nonspecific (atropine) and subtype specific-antagonists (M1-M4) were examined in organ baths. Immunohistochemical analysis of ileal muscle muscarinic receptor subtypes was correlated with contractile responses.

RESULTS

Bethanechol induced a concentration-dependent ileal contraction at all 3 age groups. Adult ileal maximal tension was 2-fold higher than that of the fetus and newborn, while 50% effective concentration (EC(50)) was similar at all ages. Atropine (10(-6)mol/L) inhibited contractility in fetal (67%+/-7%), newborn (82%+/-5%), and adult (97%+/-2%) in an age-dependent manner. The M3 antagonist exhibited robust inhibition at all age groups while the M2 antagonist demonstrated enhanced inhibition in the fetus. Immunohistochemical analysis indicated coexpression of subtype receptors in fetal, newborn, and adult ileal smooth muscle with increasing expression with advancing age.

CONCLUSION

These results demonstrate a specific developmental pattern of muscarinic receptor subtype expression. Knowledge and/or alterations of GI motility regulation may aid in the treatment of the preterm fetus or newborn.

Enhanced capacitative calcium entry and TRPC channel gene expression in human LES smooth muscle

Transient receptor potential channel (TRPC) genes encode Ca(2+)-permeable channels mediating capacitative Ca(2+) entry (CCE), which maintains intracellular Ca(2+) stores. We compared TRPC gene expression and CCE in human esophageal body (EB) and lower esophageal sphincter (LES), because these smooth muscles have distinct contractile functions that are likely associated with different Ca(2+) regulatory mechanisms. Circular layer smooth muscle cells were grown in primary culture. Transcriptional expression of TRPC genes was compared by semiquantitative RT-PCR. CCE was measured by fura 2 Ca(2+) fluorescence after blockade of sarcoplasmic reticulum Ca(2+)-ATPase with thapsigargin. mRNA for TRPC1, TRPC3, TRPC4, TRPC5, and TRPC6 was identified in EB and LES. TRPC3 and TRPC4 were more abundant in LES than EB. Basal concentration of free intracellular Ca(2+) ([Ca(2+)](i)) was similar in cells from LES (138 +/- 8 nmol/l) and EB (110 +/- 6 nmol/l) and increased with ACh (10 micromol/l; 650 +/- 28 and 590 +/- 21 nmol/l, respectively). With zero Ca(2+) in bath, thapsigargin (2 micromol/l) increased [Ca(2+)](i) more in LES (550 +/- 22 nmol/l) than EB (250 +/- 15 nmol/l, P < 0.001). Subsequent external application of 1 mmol/l Ca(2+) increased [Ca(2+)](i) more in LES (585 +/- 35 nmol/l) than EB (295 +/- 21 nmol/l, P < 0.001), indicating enhanced CCE in LES. This demonstrates CCE and TRPC transcriptional expression in human esophageal smooth muscle. In LES cells, enhanced CCE and expression of TRPC3 and TRPC4 may contribute to the physiological characteristics that distinguish LES from EB.

The intracellular pathway of the acetylcholine-induced contraction in cat detrusor muscle cells

1. The present study was aimed to investigate intracellular pathways involved in acetylcholine (ACh)-induced contraction in cat detrusor muscle cells 2. Contraction was expressed as per cent shortening of length of individually isolated smooth muscle cells obtained by enzymatic digestion. Dispersed intact and permeabilized cells were prepared for the treatment of drugs and antibody to enzymes, respectively. Using Western blot, we confirmed the presence of related proteins. 3. The maximal contraction to ACh was generated at 10(-11) M. This response was preferentially antagonized by M3 muscarinic receptor antagonist rho-fluoro-hexahydrosiladifenidol (rhoF-HSD) but not by the M1 antagonist pirenzepine and the M2 muscarinic receptor antagonist methoctramine. We identified G-proteins (Gq/11), (Gs), (G0), (Gi1), (Gi2) and (Gi3) in the bladder detrusor muscle. ACh-induced contraction was selectively inhibited by (Gq/11) antibody but not to other G subunit. 4. The phosphatidylinositol-specific phospholipase C (PI-PLC) inhibitor neomycin reduced ACh-induced contraction. However, the inhibitors of the phospholipase D, the phospholipase A2 and protein kinase C did not attenuate the ACh-induced contraction. ACh-induced contraction was inhibited by antibody to PLC-beta1 but not PLC-beta3 and PLC-gamma. Thapsigargin or strontium, which depletes or blocks intracellular calcium release, inhibited ACh-induced contraction. Inositol 1,4,5-triphosphate IP3 receptor inhibitor heparin reduced ACh-induced contraction. 5. These results suggest that in cat detrusor muscle contraction induced by ACh is mediated via M3 muscarinic receptor-dependent activation of Gq/11 and PLC-beta1 and IP3-dependent Ca(2+) release.

Characterization of a voltage-dependent Na(+) current in human esophageal smooth muscle

Smooth muscle contraction is critical to peristalsis in the human esophagus, yet the nature of the channels mediating excitation remains to be elucidated. The objective of this study was to characterize the inward currents in human esophageal smooth muscle cells (HESMCs). Esophageal tissue was isolated from patients undergoing surgery for cancer and grown in primary culture, and currents were recorded using patch-clamp electrophysiology. Depolarization elicited inward current activating positive to -40 mV and peaking at 0 mV and consisting of transient and sustained components. The transient current was half activated at -16 mV and half inactivated at -67 mV. The transient current was abolished by removal of bath Na(+) or application of TTX (IC(50) ~20 nM), whereas it persisted in the absence of bath Ca(2+) or the presence of Cd(2+). These data provide evidence that cultured HESMCs express voltage-dependent Na(+) channels. RT-PCR revealed mRNA transcripts for Na(x), the "atypical" Na(+) channel isoform, as well as Na(v)1.4. These studies provide the first evidence of Na(v)1.4 in smooth muscle and contribute to a model of excitation in HESMCs.

Possible involvement of M5 muscarinic receptor in the enhancing actions of the novel gastroprokinetic agent Z-338 on nifedipine-sensitive voltage-dependent Ca2+ currents in guinea pig stomach

We investigated the effects of the novel gastroprokinetic agent Z-338 (N-(N-N'-diisopropylaminoethyl)-[2-(2-hydroxy-4,5-dimethoxybenzoylamino)-1,3-thiazole-4-yl] carboxyamide monohydrochloride trihydrate) on L-type voltage-dependent Ca2+ currents (ICa) in guinea pig gastric myocytes by using the whole-cell patch clamp technique. Bath-applied acetylcholine (ACh) produced biphasic effects on ICa, i.e., enhancement (1-100 nM) and inhibition (1-100 microM), both of which were abolished by pretreatment with atropine (10 microM) or intracellular perfusion of GDPbetaS (500 microM). Z-338 (> or = 1 nM, ED50: 120 nM) mimicked the enhancing effects of ACh, but did not inhibit ICa. The effects of Z-338 and ACh were non-additive and blocked by atropine and GDPbetaS, but not by pertussis toxin (PTX) pretreatment (500 ng/ml). ACh (> or = 1 microM) induced slow inward currents via activation of the muscarinic receptor/PTX-sensitive G-protein pathway, but Z-338 was devoid of these effects. Neither pirenzepine (1 microM), AF-DX116 (1 microM), nor oxybutynin (100 nM) could prevent Z-338 (1 microM) and ACh (10 nM) from enhancing ICa, whilst 4-DAMP (100 nM) blocked the effects of Z-338 and ACh. Bath-application of protein kinase C (PKC) activator PDBu (phorbol-12,13-dibutyrate) (250 nM) enhanced ICa, and conversely, pipette inclusion of PKC inhibitor peptide (150 microM) abolished the effects of ACh and Z-338 on ICa. These results collectively suggest that although contribution of the M3 receptor is not excluded, the major actions of Z-338 on gastric myocytes are potentiation of ICa through activation of M5-like receptor.