Circular Muscle Cells Research Articles

The Unique Developmental Program of the Acoel Flatworm, Neochildia fusca

Acoel embryos exhibit a unique form of development that some investigators argue is related to that found in polyclad turbellarians and coelomate spiralians, which display typical quartet spiral cleavage. We generated the first cell-lineage fate map for an acoel flatworm, Neochildia fusca, using modern intracellular lineage tracers to assess the degree of similarity between these distinct developmental programs. N. fusca develops via a “duet” cleavage pattern in which second cleavage occurs in a leiotropically oblique plane relative to the animal–vegetal axis. At the four-cell stage, the plane of first cleavage corresponds to the plane of bilateral symmetry. All remaining cleavages are symmetrical across the sagittal plane. No ectomesoderm is formed; the first three micromere duets generate only ectodermal derivatives. Endomesoderm, including the complex assemblage of circular, longitudinal, and oblique muscle fibers, as well as the peripheral and central parenchyma, is generated by both third duet macromeres. The cleavage pattern, fate map, and origins of mesoderm in N. fusca share little similarity to that exhibited by other spiralians, including the Platyhelminthes (e.g., polyclad turbellarians). These findings are considered in light of the possible evolutionary origins of the acoel duet cleavage program versus the more typical quartet spiral cleavage program. Finally, an understanding of the cell-lineage fate map allows us to interpret the results of earlier cell deletion studies examining the specification of cell fates within these embryos and reveals the existence of cell–cell inductive interactions in these embryos.

Differential activation of map kinases by acetylcholine (ACh) in normal and inflamed colonic circular muscle cells

Differential activation of map kinases by acetylcholine (ACh) in normal and inflamed colonic circular muscle cells

Activation of transcription factor NF-KB in colonic circular muscle cells during inflammation: Role of oxidative stress

Activation of transcription factor NF-KB in colonic circular muscle cells during inflammation: Role of oxidative stress

Molecular alterations in ileal circular muscle cells by oxidative stress

Molecular alterations in ileal circular muscle cells by oxidative stress

The human ether-a-go-go related gene (HERG)-like potassium channel in rabbit colonic smooth muscle cells: A potential target for the actions of cisapride

We have recently identified HERG-like K+ currents in esophageal smooth muscle where it importantly contributes to the resting membrane potential (RMP)(Akbarali et aI., Am.J.Phys. 277: C1284, 1999). Drugs that block cardiac HERG channels cause abnormalities such as long Q-T syndrome, an effect that can be induced by the gastrointestinal prokinetic agent, cisapride. The aim of this study was, therefore, to determine a) the presence and role of HERG-like currents in colonic smooth muscle and b) the potential effect of cisapride on these K+ currents. Whole cell patch-clamp experiments were carried out on freshly isolated rabbit colonic circular muscle cells. The conductance of inwardly rectifying HERG-like K+ channels in cells was enhanced by perfusing with isotonic extracellular K+ solution (140 mM K+). Under these conditions, when cells were voltageclamped at 0 mV (EK ) , step hyperpolarizations to -120 mV in 10 mV increments resulted in large inward currents that activated rapidly and then slowly inactivated in a timeand voltage-dependent fashion (Tinac .= 55 ± 5ms at -120 mY; n=4). The peak current-voltage relationship showed marked inward rectification with a reversal at EK . The amplitude of peak currents at -120 mV was -170 ± 14 pA (n=26). At potentials negative to -60 mV, prominent inactivation resulting in cross-over of the currents was observed. A U-shaped voltage-dependence for non-inactivating (window) currents occured between -80 mV and -40 mV (peak amplitude of -80 ± 4 pA; n=3) suggesting contribution of the HERG-like channels to the resting potential of the smooth muscle cells. These K+ currents were completely abolished by the selective HERG channel blocker, E-4031 (I /LM; n= 10). Cisapride also dose-dependently blocked (0.001 10 /LM; n=24) the HERG-like K+ current with an ICso of I/LM. E-4031 and cisapride-sensitive currents demonstrated strong inward rectification. In further studies, the RMP of whole muscle strips was measured using high resistance microelectrodes. Cisapride (I/LM) and E-4031 (3/LM), in the presence of atropine (I/LM) and nifedipine (I/LM), depolarized the RMP from -47 ± 2 mV to -34 ± 4 mV and from -54mV ± 3mV to -37 ± 3 mY, respectively (n=3). These studies demonstrate a) that HERG-like currents in rabbit colonic smooth muscle are involved in maintaining resting potential and b) these gastrointestinal smooth muscle K+ channels, like in the heart, are potential targets for the prokinetic agent, cisapride. Supported by NIH(DK46367)

Energy storage by passive elastic structures in the mantle of sepia officinalis.

The passive elastic properties of the mantle of the cuttlefish Sepia officinalis have been characterized in experiments on intact mantle and on pieces cut from the mantle. The mantle was found to be very compliant over a wide range of circumferential strains, corresponding to a change in mantle circumferential strain of 0.45. Beyond this range of strain, the mantle was much stiffer, in both the circumferential direction, 0.542+/-0.025 MPa (mean +/- s.e.m., N=51) and through the thickness of the mantle wall, 0.152+/-0.041 MPa (N=11). Almost 80 % of the work done on the tissue during compression in the circumferential direction was recovered during elastic recoil of the tissue; this elastic work could contribute to refilling the mantle after a jet. Our estimates of the work done during a cycle of jetting and refilling show that such elastic work is small (approximately 1 %) compared with the contractile work done by the circular muscle fibres. However, although the elastic work is almost negligible in the overall energy budget, it is probably sufficient to power refilling of the mantle.

Thyrotropin-releasing hormone interacts with vasoactive intestinal peptide-specific receptor in guinea pig cecal circular smooth muscle cells

The relationship between thyrotropin-releasing hormone (TRH) binding sites and vasoactive intestinal peptide (VIP) receptors in circular muscle cells obtained from the guinea pig cecum was investigated using antagonists of VIP receptors and a selective receptor protection method. Both VIP10–28, a VIP antagonist, and atrial natriuretic peptide1–11 (ANP1–11), a VIP-specific receptor antagonist, completely inhibited 10 −5 M TRH-induced relaxation in a concentration-dependent manner. The muscle cells where cholecystokinin octapeptide (CCK-8) and TRH binding sites were protected completely preserved the inhibitory responses to TRH and ANP (a VIP-specific receptor agonist), and partially the inhibitory response to VIP. Peptide histidine isoleucine (PHI: a VIP-preferring receptor agonist) had no inhibitory effect on these cells. The muscle cells where CCK-8 and ANP (VIP-specific) receptors were protected completely preserved the inhibitory responses to TRH and ANP and partially the inhibitory response to VIP. PHI had no inhibitory effect on these cells. The muscle cells where CCK-8 and VIP receptors (both VIP-specific and VIP-preferring receptors) were protected preserved completely the inhibitory responses to TRH, VIP, ANP, and PHI. The muscle cells where CCK-8 and PHI (VIP-preferring) receptors were protected completely preserved the inhibitory response to PHI and partially the inhibitory response to VIP. TRH and ANP had no inhibitory effect on these cells. This study first demonstrates that TRH interacts with VIP-specific receptor in guinea pig cecal circular smooth muscle cells.

Impairment of Ca(2+) mobilization in circular muscle cells of the inflamed colon.

This study investigated whether inflammation modulates the mobilization of Ca(2+) in canine colonic circular muscle cells. The contractile response of single cells from the inflamed colon was significantly suppressed in response to ACh, KCl, and BAY K8644. Methoxyverapamil and reduction in extracellular Ca(2+) concentration dose-dependently blocked the response in both normal and inflamed cells. The increase in intracellular Ca(2+) concentration in response to ACh and KCl was significantly reduced in the inflamed cells. However, Ca(2+) efflux from the ryanodine- and inositol 1,4, 5-trisphosphate (IP(3))-sensitive stores, as well as the decrease of cell length in response to ryanodine and IP(3), were not affected. Heparin significantly blocked Ca(2+) efflux and contraction in response to ACh in both conditions. ACh-stimulated accumulation of IP(3) and the binding of [(3)H]ryanodine to its receptors were not altered by inflammation. Ruthenium red partially inhibited the response to ACh in normal and inflamed states. We conclude that the canine colonic circular muscle cells utilize Ca(2+) influx through L-type channels as well as Ca(2+) release from the ryanodine- and IP(3)-sensitive stores to contract. Inflammation impairs Ca(2+) influx through L-type channels, but it may not affect intracellular Ca(2+) release. The impairment of Ca(2+) influx may contribute to the suppression of circular muscle contractility in the inflamed state.

Ultrastructural and histochemical characterization of special muscle cells in the monkey small intestine.

The ultrastructure, three-dimensional arrangement, and histochemical features of special muscle cells in the monkey small intestine were investigated. The cells formed a special layer separated from the main part by a connective tissue space along the submucosal surface of the circular muscle coat. Scanning electron microscopy using alkali maceration demonstrated this inner sublayer to be a continuous thin sheet consisting of irregularly-shaped muscle cells equipped with many cytoplasmic projections and caveolae. Other ultrastructural features included direct contact with interstitial cells, due to their close association with nerve fibers of the deep muscular plexus. Histochemical examination revealed significant alkaline phosphatase activity and immunoreactivity for vascular smooth muscle alpha actin in these muscle cells, whereas the ordinary circular muscle cells were immunopositive for enteric smooth muscle gamma actin. These findings suggest that the special muscle cells play an important role in regulating the radial stretch of the monkey small intestinal wall.

Physiological significance of hyperpolarization-activated inward currents (I h) in smooth muscle cells from the circular layers of pregnant rat myometrium

The properties of hyperpolarization-activated current in pregnant rat uterus (17-19 days gestation) were investigated using microelectrode and patch-clamp techniques, and isometric tension recording. The resting membrane potentials were -58.4 mV and -48.5 mV in longitudinal and circular muscle cells, respectively. Application of hyperpolarizing current pulses produced a time-dependent anomalous inward rectification of membrane potential only in circular muscle cells. Under voltage-clamp conditions, inward currents (Ih) were activated by long hyperpolarizing pulses below -60 mV in circular but not in longitudinal muscle cells. Application of extracellular but not intracellular Cs+ reduced the amplitude of I(h) in a concentration-dependent manner (an IC50( of 0.15 mM). The reversal potential for Ih was -26.2 mV and the slope conductance was 5 nS/pF. Changes in [K+]o and [Na+]o shifted the reversal potential, and Ih amplitude increased with excess [K+]o and decreased with low [Na+]o. The steady-state activation of Ih was well fitted by a Boltzmann equation with a half-activation potential of -84.3 mV and a slope factor of 9.6 mV. Time courses of activation and deactivation of the current strongly depended on membrane potential, and were well fitted by a single exponential function. The activation time constant of Ih was dependent on temperature. In isometric tension recording, application of extracellular Cs+ to the circular muscles reduced the frequency, but not the amplitude, of spontaneous contractions in a concentration-dependent manner. It is concluded that in pregnant rat uterus Ih channels are predominantly distributed in smooth muscle cells from the circular layer. Since Ih is activated at the resting membrane potential, it is likely that this current contributes to the maintenance of resting membrane potential and spontaneous activity in circular smooth muscle cells of late pregnant rats.

Gap junctions in intestinal smooth muscle and interstitial cells of Cajal.

This manuscript reviews gap junctions' roles in control of intestinal motility. Gap junctions (GJs) of small intestine (SmIn) are found between circular muscle (CM) cells, between interstitial cells of Cajal (ICC) of deep muscular plexus (DMP) and between them and adjacent outer circular muscle (OCM). GJs between longitudinal muscle (LM) cells or between cells of inner circular muscle (ICM) have not been reported. Occasional GJs have been reported between ICC of the myenteric plexus (MyP) and rarely between these ICC and adjacent LM or CM cells, or between ICC within CM and smooth muscle cells. In the colon (Co) of several species a special network of ICC lines the inner border of CM, the submuscular plexus (SP). GJs are found between ICCs and between them and CM cells. The ICC of MyP of Co are associated with LM and CM; occasional GJs exist between ICC and each muscle layer. Small GJs are missed by electron microscopy or light microscopic Immunocytochemistry. Therefore, GJ coupling may exist without demonstrated GJs. The consequences for the pacemaking functions of ICC networks of varied densities of GJ between ICC and between ICC of MyP or DMP or of SP and CM are considered. Connexins (Cxs) that compose intestinal GJs may affect coupling, but are incompletely known. Understanding of the role of GJs in coordinating intestinal motility requires knowing: (1) what passes through gap junctions to couple ICC to smooth muscle cells; (2) what Cx with what conductances and what modulatory controls connect ICC and smooth muscle cells; (3) whether smooth muscles can generate slow waves independent of ICC networks; and (4) what happens to motility, slow waves, and IJPs when GJs are selectively uncoupled.

Serotonergic responses of the siphons and adjacent mantle tissue of the zebra mussel, Dreissena polymorpha

Bivalve siphons have important functional roles in nutritional physiology, defense, and reproductive mechanisms, yet little is known about their neuromuscular control. In the present study, tension measurements and video observations of siphons and adjacent mantle tissue were used to investigate responses to serotonin (5-HT). 5-HT caused relaxation at 10 −6 M and 10 −5 M, contraction or biphasic responses at 10 −4 M and 10 −3 M, and siphon opening at 10 −4 M and 10 −3 M. Responses were slow and lasted 5–10 min after much shorter (20 s) applications of 5-HT. The relaxation phase was enhanced in high potassium medium. Contractile responses could be mimicked by α-1-methyl-5-HT and 2-methyl-5-HT but not by 8-OH-DPAT. The responses were not affected by methiothepin, TFMPP, 1-(1-naphthyl)piperazine, metergoline, NAN-190, mianserin, cyproheptadine, and ketanserin. The pharmacology of the 5-HT receptor(s) mediating these siphon/mantle responses is, therefore, different from previously described 5-HT receptors involved in spawning. The siphon/mantle contains previously undescribed longitudinal muscle fibers in the mantle and circular muscle fibers around the siphons. Serotonergic innervation of the siphon margins and mantle tissue was observed by immunohistology. The presence of 5-HT in the siphon/mantle tissue and the responsiveness of these preparations to 5-HT suggest that 5-HT may be a physiological regulator of mantle and siphon movements in the zebra mussel.

Control systems of gastrointestinal motility are immature at birth in dogs.

Networks of interstitial cells of Cajal (ICC) in the myenteric plexus (Myp) or circular muscle (CM) function as pacemakers for gastrointestinal slow waves. ICC in contact with muscle and closely associated with nerves in the CM may mediate inhibitory neurotransmission. We wondered if ICC in Myp and CM and their connections are immature at birth and mature first in the proximal gut in association with nerves. Tissues from lower esophageal sphincter (LES), pylorus (PYL), small intestine (SI) and colon (CO) of 18 term fetal dogs taken from six females were fixed and prepared for ultrastructural examination and studied. Ganglia were present where expected in the Myp and submucous plexus (SMP). ICC cells were present in the Myp of PYL, SI and CO and appeared to have normal relationships to the outer border of CM as in adults. ICC in CM were found associated with nerves in the LES and in PYL, but not in SI or CO. However, axons in CM were everywhere usually free of glial covering, indicating ongoing migration or development. No organized deep muscular plexus (DMP) in SI or submuscular plexus (SP) in colon was present. Visible gap junctions were absent everywhere except for very rare ones between circular muscle cells. We conclude that at birth the neural and ICC networks of CM are more immature in intestine and colon than in oesophagus and stomach. Development of nerve and ICC of CM in oesophagus and stomach apparently precedes that in the remaining gut. However networks in these regions have not achieved adult organization and ICC and smooth muscle cells are anatomically poorly coupled. These findings suggest the reasons that gut motility at birth will not be adult in pattern are because ICC, nerve and muscle control systems are not fully differentiated. Further developmental delays in ICC and nerve maturation could have serious consequences for feeding of infant animals.

Neuromuscular control of esophageal peristalsis.

The esophagus is a muscular conduit connecting the pharynx and the stomach. Its function is controlled by an intrinsic nervous system and by input from the central nervous system through the vagus nerve. Peristalsis in its striated muscle is directed by sequential vagal excitation arising in the brain stem, whereas peristalsis in its smooth muscle involves complex interactions among the central and peripheral neural systems and the smooth muscle elements of the esophagus. The peripheral neuronal elements responsible for producing esophageal off-response, relaxation of the lower esophageal sphincter, and hyperpolarization of the circular esophageal muscle cells reside in the myenteric plexus of the esophagus. For many years these nerves were considered nonadrenergic and noncholinergic because the inhibitory neurotransmitter released on their activation was unknown. We now know that nitric oxide or a related compound is that inhibitory neurotransmitter. The primary excitatory neurotransmitter controlling esophageal motor function is acetylcholine. Some disorders of esophageal motor function, including diffuse esophageal spasm and achalasia, may result from defects in or an imbalance between these excitatory and inhibitory neuromuscular systems.

Whole-mount NADPH-diaphorase histochemistry is a reliable technique for the intraoperative evaluation of extent of aganglionosis.

Multiple seromuscular biopsies at three levels (narrow segment, transitional zone, and dilated segment) were taken and investigated intraoperatively to determine the extent of aganglionosis. Using the whole-mount preparation technique, circular muscle fibers were separated from the specimens. After a short prefixation, the muscle fibers were stained by the NADPH-diaphorase technique and were examined within 20-25 min. A fine and dense neuronal meshwork was observed between circular muscle fibers in the normal and ganglionic part of the bowel. In contrast, there was a complete lack of NADPH-diaphorase-positive fibers in the circular muscle of aganglionic colon. In the transitional zone, NADPH-diaphorase-positive fibers were markedly reduced compared to the ganglionic region. The density of these fibers increased and attained normal levels in the proximal bowel above the transition zone. These results suggest that whole-mount NADPH-diaphorase histochemistry is a three-dimensional technique suitable for the intraoperative evaluation of extend of aganglionosis. The technique is sufficiently rapid to be used in conjunction with routine frozen sections to assist in the diagnosis and in selecting the optimal level of resection at the time of pull-through operation.

Description of growth in the tropical cuttlefish Sepia elliptica using muscle tissue

The mantle muscle tissue of cuttlefish is predominantly made up of circular muscle fibres which run around the body. This circular muscle tissue is divided into discrete blocks by radial fibres, which run perpendicular to the main axis of the body. Growth of mantle muscle tissue was described in the tropical cuttlefish Sepia elliptica by examining muscle block size and the density and size distribution of muscle fibres. Changes in these variables were assessed in juvenile and adult cuttlefish. Generation of new muscle fibres, both within new and existing muscle blocks, occurred as animals grew across the size range. Anterior muscle blocks were smaller than muscle blocks in the middle and posterior regions of the mantle, suggesting that new blocks were generated anteriorly. Muscle blocks were also created in the middle and posterior regions by division of existing large blocks into small blocks by generation of circular and radial muscle fibres. The examination of cuttlefish muscle growth dynamics provided an alternative way of assessing cephalopod growth mechanisms.

Initiation of peristalsis by circumferential stretch of flat sheets of guinea-pig ileum.

1. Segments of isolated guinea-pig intestine, 12 mm long, were distended slowly by intraluminal fluid infusion or by mechanical stretch as either a tube or flat sheet. In all cases, at a constant threshold length, a sudden, large amplitude contraction of the circular muscle occurred orally, corresponding to the initiation of peristalsis. 2. Circumferential stretch of flat sheet preparations evoked graded contractions of the longitudinal muscle (the 'preparatory phase'), which were maintained during circular muscle contraction. This suggests that the lengthening reported during the emptying phase of peristalsis is due to mechanical interactions. 3. The threshold for peristalsis was lower with more rapid stretches and was also lower in long preparations (25 mm) compared with short preparations (5-10 mm), indicating that ascending excitatory pathways play a significant role in triggering peristalsis. 4. Stretching a preparation beyond the threshold for peristalsis evoked contractions of increasing amplitude; thus peristalsis is graded above its threshold. However, during suprathreshold stretch maintained at a constant length, contractions of the circular muscle quickly declined in amplitude and frequency. 5. Circular muscle cells had a resting membrane potential approximately 6 mV more negative than the threshold for action potentials. During slow circumferential stretch, subthreshold graded excitatory motor input to the circular muscle occurred, prior to the initiation of peristalsis. However, peristalsis was initiated by a discrete large excitatory junction potential (12 +/- 2 mV) which evoked bursts of smooth muscle action potentials and which probably arose from synchronized firing of ascending excitatory neuronal pathways.

Slow waves in circular muscle of porcine ileum: structural and electrophysiological studies.

The structural and functional bases of pacemaking (slow waves) in porcine ileal circular muscle were studied. The myenteric plexus contained two, structurally distinct types of interstitial cells of Cajal (ICC) interconnected by gap junctions and connected by close contacts to muscle layers. At the deep muscular plexus, ICC were present, not regularly close to nerve axons or in gap junction contact with one another or outer circular muscle, which had many gap junctions. Slow waves (5.2 +/- 2 mV amplitude and 4.6 +/- 0.7 s duration) occurred at 9.9 +/- 1.1 counts/min. Tissue length and time constants were 2.00 +/- 0.3 mm and 111 +/- 37 ms, respectively. Large electrical field-induced hyperpolarizations or depolarizations reduced amplitudes but not frequencies or durations of slow waves; hyperpolarizations progressively reduced inhibitory junction potentials as if the K+ channel opening mediated them. In conclusion, the myenteric plexus ICC of pig ileum, which appears to pace the muscle layers, appears insensitive to voltages applied to the syncytium of circular muscle cells. Limited coupling between ICC and circular muscle or voltage-insensitive pacemaking activity may explain these findings.

The anatomy and taxonomy ofAmorphonemertes kubergensisgen. et sp. nov. (Nemertini) from the Tromsø area (Norway)

Abstract The anatomy and taxonomy of a new heteronemertine, Amorphonemertes kubergensis are described and illustrated. The species is characterized by, inter alia, a thick paleonemertine-like basement membrane, a proboscis with four nerves and three muscle layers with single and groups of longitudinal muscle fibres in the outer longitudinal muscle layer, well developed subepidermal circular muscle fibres in the posterior brain and mouth regions and well-developed longitudinal muscle fibres (horizontal muscle plate) dorsal to the foregut. The material was collected in the Tromsø area (Norway).

Interstitial cells of Cajal: mediators of communication between circular and longitudinal muscle layers of canine colon.

The network of interstitial cells of Cajal associated with Auerbach's (myenteric) plexus in the canine colon was investigated to determine its role in facilitating communication between circular and longitudinal muscle layers. Electrical coupling between the muscle layers was demonstrated by propagating extracellularly evoked electrotonic pulses from circular muscle cells to nearby longitudinal muscle cells. The likelihood of cytoplasmic continuity across Auerbach's plexus was further demonstrated by the ability of neurobiotin to spread between the interstitial cells and the circular and longitudinal muscle cells. Importantly, direct neurobiotin spread between circular and longitudinal muscle cells was not observed even when they were in close proximity as determined by confocal microscopy. When neurobiotin did spread across the two muscle layers, the intervening interstitial cells were always neurobiotin-positive. In regions where circular and longitudinal muscle cells approach each other closely, electron microscopy revealed the presence of close appositions between interstitial cells and smooth muscle cells. Gap junctions between interstitial cells and smooth muscle cells of both layers, as judged by electron microscopy, were extremely rare. Neither gap junctions nor close appositions were observed between longitudinal and circular muscle cells. The special arrangement for electrotonic coupling across Auerbach's plexus through interstitial cells of Cajal suggests controlled coupling between the two muscle layers, explaining the preservation of their distinct electrical activities.