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At least 19 recordsLinked to original sources
PubMed1999

Ectonucleotidases of avian gizzard smooth muscle and liver plasma membranes: a comparative study.

Extracellular nucleotides, e.g., ATP, ADP, and UTP, are important signaling molecules which elicit various physiological responses in different tissues. Their degradation is catalyzed by ectonucleotidases which are located on cell surfaces. Most tissues have a mixed population of ectonucleotidases. In this report, the ATP and ADP hydrolyzing ectonucleotidases of chicken gizzard smooth muscle and liver plasma membranes were studied. The two membranes exhibited marked differences in the ratio of ATPase/ADPase activities, activation by divalent cations, thermal stability, responses to detergents and cross-linking agents, and sensitivity to several enzyme inhibitors. The ATPase activity of chicken gizzard membranes is (i) labile to heat and detergents; (ii) activated by concanavalin A and disuccinimidyl suberate, both cross-linking agents; (iii) inhibited by mercurials; and (iv) insensitive to high concentrations of azide, a known inhibitor of ecto-ATP diphosphohydrolases (ecto-ATP/Dase). In contrast, the liver membrane ATPase and ADPase activities are more stable to treatment by heat and detergents and insensitive to cross-linking agents and mercurials, but are inhibited by azide. A low ADP hydrolase activity in the gizzard membranes could be distinguished from both the gizzard ATPase and the liver ATPase/ADPase. This ADP hydrolase, which is markedly stimulated by NBD-Cl, accounts for most of the ADP hydrolysis activity in gizzard membranes. It is concluded that the major ectonucleotidase in the gizzard membranes is an ecto-ATPase whereas that in the liver membranes is an ecto-ATP/Dase. That both membranes contain a mixed population of the ecto-ATPase and ecto-ATP/Dase, but in different proportions, is further demonstrated by immunochemical characterization. The different composition of ectonucleotidases in the two membranes is expected to have an important effect on the regulation of hydrolysis of extracellular ATP as well as the concentration of extracellular adenine nucleotides in the gizzard and liver tissues.

4-Chloro-7-nitrobenzofurazan↗
PubMed1993

Development of vagal innervation to the muscle of the avian gizzard.

The development of the vagal innervation to the gizzard has been investigated in chick embryos and young chicks. The membrane potential, first measurable on the 15th day of incubation, was -54 +/- 0.5 mV and increased with development to -67 +/- 0.4 mV. The latter value was attained 5 days after hatching and persisted thereafter. Stimulation of intramural nerves elicited a cholinergic, excitatory junction potential (EJP) for the first time, only in a small fraction of cells, on the 20th day of incubation. Within 3 days after hatching, cholinergic transmission showed the same features as in older chicks. Stimulation of the vagus nerve elicited no membrane potential responses before hatching but as early as 4 days after hatching, non-adrenergic, inhibitory junction potentials (IJPs) were evoked. In the next 10 days or so, the IJP was replaced with a cholinergic EJP as seen in mature tissues. After atropine (0.1-1 microM) treatment, both vagal and intramural nerve stimulation evoked a non-adrenergic IJP in a small fraction of cells immediately after hatching. The fraction of cells exhibiting the IJP increased with growth and reached 100% 5 days after hatching. Hexamethonium (50 or 100 microM) abolished the vagally-evoked EJPs. The vagally-evoked IJPs remained unchanged after application of hexamethonium in the early days after hatching, but later they were abolished in about half of the cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1969

The effects of hyoscine and anticholinesterases on cholinergic transmission to the smooth muscle cells of the avian gizzard.

1. Intracellular recordings were made from smooth muscle cells of the pigeon and chick gizzards. Hyoscine (10(-6) g/ml.) blocked, within 2 min, the excitatory junction potentials (E.J.P.s) evoked by transmural stimulation. As the amplitudes of E.J.P.s decreased, their durations also decreased. Hyoscine had no effect on the inhibitory junction potentials (I.J.P.s) evoked by transmural stimulation.2. Initially, physostigmine or neostigmine (10(-7) - 5 x 10(-6) g/ml.) caused a marked increase in the amplitudes of E.J.P.s, without affecting their time courses. Sometimes, anticholinesterases caused a single stimulus to evoke multiple E.J.P.s.3. After several minutes in the presence of high concentrations (10(-6) - 5 x 10(-6) g/ml.) of anticholinesterases the muscle cells were depolarized by about 15-20 mV, and thus the amplitudes of I.J.P.s evoked by transmural stimulation were larger than under control conditions. E.J.P.s summed at much lower stimulation frequencies than normal, an observation which indicated that high concentrations of anticholinesterases increased the durations of the E.J.P.s. Repetitive stimulation evoked a membrane depolarization which persisted for as long as 10 sec after stimulation was stopped.4. These results are discussed in terms of the action of the drugs at the nervesmooth muscle junction and on ganglion cells in the myenteric plexus.

Animals↗
PubMed1989

Unique geometry of actin-membrane anchorage sites in avian gizzard smooth muscle cells.

Adherens junctions in isolated avian gizzard smooth muscle cells appear as short longitudinal streaks or chevrons that are arranged in periodic, mainly transverse bands along the cell surface. This barrel-like geometry, revealed by antibodies to either vinculin or talin, was seen also in teased gizzard strips by confocal laser-scanning microscopy and contrasted with the rib-like surface pattern observed here and previously in other avian and mammalian smooth muscles. There were on average 67 transverse bands per gizzard cell and an estimated total of around 800 vinculin/talin sites. The longitudinal spacing between the transverse bands of vinculin streaks in the gizzard cells changed from 4-5 microns in extended cells to around 1 micron in shortened cells and the bands remained essentially transverse at all cell lengths, inconsistent with a screw-like mode of cell shortening as has been invoked for smooth muscle cells by others. The absence of rotation on shortening was confirmed by observations on isolated and bead-decorated skinned cells that were induced to contract with ATP. Counterlabelling of cells with alpha-actinin antibodies produced more or less exclusive staining of the cytoplasmic dense bodies, and little surface label: the total number of dense bodies per cell, estimated from confocal microscope through focal series was in the range of 3000. The data are consistent with a periodic anchorage of actin filaments to the cell surface and, in turn, with the existence of regularly spaced contractile assemblies.

Animals↗
PubMed1969

Nerve-mediated excitation and inhibition of the smooth muscle cells of the avian gizzard.

1. The electrical events evoked in smooth muscle cells of the chick and pigeon gizzards by vagal, perivascular sympathetic and transmural stimulation were recorded with intracellular micro-electrodes.2. Single stimulating pulses applied to the extrinsic nerves, or to intrinsic fibres, produced excitatory junction potentials (E.J.P.s) which were blocked by hyoscine. Repetitive stimulation caused facilitation of E.J.P.s and, at higher frequencies, summation. When the tissue was well oxygenated, maximal stimulation evoked action potentials and the tissue contracted. If the tissue was allowed to become anoxic, action potentials were blocked and thus junctional transmission could be observed uncomplicated by tissue contraction.3. Cholinergic E.J.P.s appeared to be due to stimulation of both post-ganglionic neurones and the pre-ganglionic input to post-ganglionic neurones, since ganglion-blocking drugs abolished the late phase of complex E.J.P.s while leaving unaffected their initial components.4. Repetitive perivascular sympathetic stimulation, after cholinergic E.J.P.s had been blocked by hyoscine, evoked a slow, long-lasting depolarization of the muscle cells. This depolarization was blocked by guanethidine (5 x 10(-6) g/ml.) and was mimicked by noradrenaline (10(-7) g/ml.).5. Under non-anoxic conditions, the tissue underwent rhythmical contractions which were associated with action potential firing. When the tissue was anoxic action potentials were not seen, but spontaneous membrane depolarizations resembling E.J.P.s were observed. Spontaneous miniature excitatory junction potentials (M.E.J.P.s) were observed only infrequently whether the tissue was well oxygenated or not.6. Single stimulating pulses applied to extrinsic or intrinsic nerves frequently evoked inhibitory junction potentials (I.J.P.s) in smooth muscle cells of the gizzards of both birds. I.J.P.s were blocked by tetrodotoxin (10(-7) g/ml.). Repetitive stimulation of inhibitory nerves gave rise to a membrane hyperpolarization; when stimulation was stopped the membrane potential showed rebound depolarization.7. These results are discussed in terms of the autonomic innervation of the avian gizzard, and possible explanations of the various types of activity observed are considered.

Action Potentials↗
PubMed1999

Phenotypic flexibility of the avian gizzard: rapid, reversible and repeated changes of organ size in response to changes in dietary fibre content

Evolutionary biology presumes that organ capacities match their natural loads. Therefore, in fluctuating conditions, organ systems are expected to show a reversible, repeatable and rapid phenotypic response that is directional and scaled. In this study, phenotypic responses of the gizzard of adult Japanese quail (Coturnix japonica) to experimental mismatches of load and capacity were tested by a series of diet-switching experiments, involving an increased content of non-digestable fibre (NDF) in the diet. The results of all experiments were in accordance with the predictions of the hypothesis that there is matching between loads and capacities. (1) The observed phenotypic responses are directional and scaled to the demands, i.e. increasing NDF elicits an increase in gizzard size. When the proportion of NDF in the diet was raised from 1 % to 45 %, the gizzard was more than twice as large as in the control group. (2) Size responses were reversible, and reduced NDF was followed by a decrease of gizzard size. (3) Phenotypic responses could be elicited repeatedly in three successive trials. (4) Excess capacities were downregulated and insufficient capacities were upregulated. (5) The responses followed changes of loads with almost no time lag, with size changes measurable within 24 h.

Journal Article↗
PubMed1987

Salt dependent dimerisation of caldesmon.

Using analytical gel filtration (FPLC) we show here that avian gizzard caldesmon (chain molecular mass 150 kDa) self-associates to form end-to-end dimers. Increasing salt concentration promotes dimerisation: at 150 mM KCl, about 40% of the caldesmon was dimeric. Freshly gel filtered caldesmon had an actin gelating activity which decreased with increasing ionic strength. At 150 mM KCl, caldesmon at a 1:90 molar ratio to actin doubled the low shear viscosity of F-actin. Sixfold less filamin was required to produce the same effect.

Animals↗
PubMed1990

The cytoskeletal and contractile apparatus of smooth muscle: contraction bands and segmentation of the contractile elements.

Confocal laser scanning microscopy of isolated and antibody-labeled avian gizzard smooth muscle cells has revealed the global organization of the contractile and cytoskeletal elements. The cytoskeleton, marked by antibodies to desmin and filamin is composed of a mainly longitudinal, meandering and branched system of fibrils that contrasts with the plait-like, interdigitating arrangement of linear fibrils of the contractile apparatus, labeled with antibodies to myosin and tropomyosin. Although desmin and filamin were colocalized in the body of the cell, filamin antibodies labeled additionally the vinculin-containing surface plaques. In confocal optical sections the contractile fibrils showed a continuous label for myosin for at least 5 microns along their length: there was no obvious or regular interruption of label as might be expected for registered myosin filaments. The cytoplasmic dense bodies, labeled with antibodies to alpha-actinin exhibited a regular, diagonal arrangement in both extended cells and in cells shortened in solution to one-fifth of their extended length: after the same shortening, the fibrils of the cytoskeleton that showed colocalization with the dense bodies in extended cells became crumpled and disordered. It is concluded that the dense bodies serve as coupling elements between the cytoskeletal and contractile systems. After extraction with Triton X-100, isolated cells bound so firmly to a glass substrate that they were unable to shorten as a whole when exposed to exogenous Mg ATP. Instead, they contracted internally, producing integral of 10 regularly spaced contraction nodes along their length. On the basis of differences of actin distribution two types of nodes could be distinguished: actin-positive nodes, in which actin straddled the node, and actin-negative nodes, characterized by an actin-free center flanked by actin fringes of 4.5 microns minimum length on either side. Myosin was concentrated in the center of the node in both cases. The differences in node morphology could be correlated with different degrees of coupling of the contractile with the cytoskeletal elements, effected by a preparation-dependent variability of proteolysis of the cells. The nodes were shown to be closely related to the supercontracted cell fragments shown in the accompanying paper (Small et al., 1990) and furnished further evidence for long actin filaments in smooth muscle. Further, the segmentation of the contractile elements pointed to a hierarchial organization of the myofilaments governed by as yet undetected elements.

Actinin↗
PubMed1994

Antibodies probe for folded monomeric myosin in relaxed and contracted smooth muscle.

Regulatory light chain phosphorylation is required for assembly of smooth and non-muscle myosins in vitro, but its effect on polymerization within the cell is not understood. Relaxed smooth muscle cells contain dephosphorylated thick filaments, but this does not exclude the presence of a pool of folded myosin monomers which could be recruited to assemble when phosphorylated, thus forming part of smooth muscle's activation pathway. To test this hypothesis, relaxed and contracted avian gizzard cryosections were labeled with a fluorescently conjugated monoclonal antibody specific for the folded monomeric conformation, or with an antibody against the tip of the tail whose epitope is accessible in the monomeric but not the filamentous state. Fluorescence intensity observed in the two physiological states was quantitated by digital imaging microscopy. Only trace amounts of folded monomeric myosin were detected in both the relaxed and contracted states. The amount of monomer also did not increase when alpha-toxin permeabilized gizzard was equilibrated in a solvent that disassembles filaments in vitro. Assembly/disassembly is therefore unlikely to play a major role in regulating the contraction/relaxation cycle in smooth muscle cells.

Animals↗
PubMed1991

Identification of the site phosphorylated by casein kinase II in smooth muscle caldesmon.

Phosphorylation of avian gizzard caldesmon by casein kinase II was investigated. The enzyme incorporates about 1 mol of phosphate per mol of caldesmon. All sites of phosphorylation are located in short chymotryptic peptides with Mr 25-27 kDa or in the short N-terminal peptide formed after cleavage of chicken gizzard caldesmon at Cys153. The primary structure of the tryptic peptide containing the main site of duck gizzard caldesmon phosphorylation is S-E-V-N-A-Q-N-X-V-A-E-D-E-T-K, where X is an unidentified residue, presumed to be phosphoserine. Thus, Ser73 is the main site phosphorylated by casein kinase II in avian gizzard caldesmon.

Amino Acid Sequence↗
PubMed1998

Integrin expression in developing smooth muscle cells.

We studied the specific expression patterns and distributions of alpha1 and beta1 integrin subunits, the major cell adhesion receptors in smooth muscle, in developing smooth muscle cells from 16-, 18-, and 20-day embryonic gizzards and from 1- and 7-day post hatch chick gizzards by SDS-PAGE, immunoblotting, and immunoelectron microscopy. Antibodies raised against alpha1 and beta1 integrins isolated from avian gizzards were used as probes. Gels and blots showed that the amount of alpha1 and beta1 integrins increased as age increased, with major increases at 1 and 7 days post hatch. Image analysis of immunoelectron micrographs demonstrated that statistically significant labeling increases occurred between embryonic Days 16 and 18, between embryonic Day 20 and 1 day post hatch, and between 1 day and 7 days post hatch. Immunolabeling with both anti-alpha1 and anti-beta1 integrin was prominent at membrane-associated dense plaques (MADPs) and at filament anchoring regions at cell ends. This indicates that alpha1 and beta1 integrin expression coincides temporally with the intracellular proliferation and reorientation of myofilaments. The similarity in distribution patterns of alpha1 and beta1 integrins during development suggests that the two integrin subunits are synchronously expressed during development and do not appear sequentially. (J Histochem Cytochem 46:119-125, 1998)

Animals↗
PubMed1987

Metavinculin and vinculin from mammalian smooth muscle: bulk isolation and characterization.

Metavinculin, a vinculin related protein found only in muscle, has been prepared in bulk amounts from porcine stomach by a new procedure: the same procedure is applicable to the purification of vinculin from porcine stomach and avian gizzard. A comparison of the mammalian and avian proteins by peptide mapping showed them all to contain a common protease resistant 90 kDa core; however both avian and mammalian vinculins were notably more resistant to proteolysis down to this core than their respective metavinculins. Despite the close similarities in the peptide maps, in molecular weight and amino acid composition neither of the mammalian proteins exhibited the head and tail morphology formerly described for gizzard vinculin and metavinculin; both porcine proteins appeared globular under the electron microscope. From the gross variability in the ratios of metavinculin to vinculin among smooth muscles of different origin as well as from the common detergent-independent solubility properties of both proteins during isolation, it is concluded that vinculin and metavinculin perform duplicatory roles as peripheral membrane components. No definitive evidence for the interaction of either protein with actin filaments was obtained.

Animals↗
PubMed1997

Localization of smoothelin in avian smooth muscle and identification of a vascular-specific isoform.

Smoothelin is a smooth muscle-specific protein of minor abundance first identified via a monoclonal antibody obtained using an avian gizzard extract as antigen. Dual labelling of ultrathin sections with antibodies to smoothelin together with antibodies to other smooth muscle proteins showed that smoothelin was co-distributed with filamin and desmin in the cytoskeleton domain of the smooth muscle cell. From the finding that smoothelin, unlike desmin, was readily extracted by Triton X-100 as well as under conditions that solubilized myosin, beta-actin and filamin, we conclude that smoothelin is most likely associated with the actin cytoskeleton. Western blot analysis of gizzard smooth muscle tissue revealed an immunoreactive protein band with an apparent molecular weight of 59 kDa that separated into 3-4 isolated variants, while avian vascular muscle showed a polypeptide band of 95 kDa. These results point to the presence of specific isoforms in visceral and vascular smooth muscles. The 59 kDa isoform was shown to be distinct from the 60 kDa filamin-binding protein, described by Maekawa and Sakai (FEBS Lett. 221, 68-72, 1987). As compared to other smooth muscle markers, such as calponin and SM22, smoothelin appeared very late during differentiation in the chick gizzard, on about the 18th embryonic day.

Animals↗