A sensitive SDS-PAGE method separating myosin heavy chain isoforms of rat skeletal muscles reveals the heterogeneous nature of the embryonic myosin

Myosin isoforms are used as markers of heterogeneity and plasticity of skeletal muscle fibers and motor units. Tedious and time-consuming methods, needing microgram or milligram amounts of myosin are widely used to characterize the heavy subunits. We here describe a sensitive method that separates in nanogram or microgram amounts the heavy chains of immature, fast and slow adult rat muscles in complex mixtures of myosins. Though the method is assembled from published procedures (SDS-PAGE, peptide mapping in the presence of SDS, silver stain) for the logical extensions introduced the end-product is a powerful tool to separate and characterize these high molecular weight biopolymers until now inseparable from complex mixtures. The method reveals the heterogeneous nature of the embryonic myosin heavy chains.

Ultrastructure, function and composition of smooth muscle

Filamentous myosin is present in both relaxed (myosin light chains unphosphorylated) and contracted (light chains phosphorylated) vascular smooth muscle. The organization of myosin and actin filaments and the insertion of the latter on cytoplasmic and plasma membrane bound dense bodies is consistent with a mini sarcomere-like organization and a sliding filament mechanism of contraction in smooth muscle. Mitochondria are high capacity, low affinity Ca stores in smooth muscle. They do not play a role in the regulation of cytoplasmic Ca2+ at physiological levels. The localization and Ca content of the junctional sarcoplasmatic reticulum (SR) is consistent with this organelle being the major intracellular source of activator Ca released by excitatory transmitters. Repeated contractions in the absence of extracellular Ca2+ (thought to represent recycling of intracellular activator Ca2+) can be demonstrated if the excitatory agent is not allowed to remain in contact with the smooth muscle throughout relaxation.; the demonstration of "recycling" is facilitated if the efflux of cellular Ca2+ is blocked. The rise in total cytoplasmic calcium measured with electron probe analysis during a maintained (30 min) contracture in rabbit portal-anterior mesenteric vein smooth muscle (approximately 0.9 mol/kg dry cytoplasm) is greater than the amount of Ca that could be bound to calmodulin.

Selective purification of the 20,000-Da light chains of smooth muscle myosin

The 20,000-Da light chains of gizzard smooth muscle myosin have been purified to homogeneity. Actomyosin, prepared by MgATP extraction of myofibrils, was denatured in 8 M urea, 1 M guanidine HCl, and 0.05% sodium dodecyl sulfate. Myosin heavy chains were precipitated with ethanol and the light chain enriched fraction was dialyzed and subjected to chromatography on DEAE-Sephacel. Fractions containing the 20,000-Da light chains were further purified by hydrophobic chromatography on phenyl-Sepharose. The 20,000-Da light chains eluted at low ionic strength from the phenyl-Sepharose column were judged to be greater than 95% pure by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and contained only 0.04 mol of phosphate/mol of light chain. The yield of light chains was calculated to be 219 +/- 17 mg/kg of starting gizzard smooth muscle. This method may be useful for preparation of homogeneous 20,000-Da smooth muscle myosin light chains in the quantities necessary for study of contractile systems.

Immunoreactivity of paraffin-embedded normal tissues and mesenchymal tumors for smooth muscle myosin

Immunohistochemical study of smooth muscle myosin, a protein distinct from skeletal, cardiac, or nonmyogenous myosins in paraffin-embedded normal tissues and benign and malignant mesenchymal tumors revealed its strong expression in normal smooth muscle, capillary endothelium, and pericytes. All benign smooth muscle tumors with exception of gastric leiomyomas and few other leiomyomas of the gastrointestinal tract displayed strong or moderate immunoreactivity. On the other hand, strong or moderate immunoreactivity was detected in only eight of 28 spindle-cell leiomyosarcomas, as well as in 13 out of 27 malignant fibrous histiocytomas and three out of nine malignant hemangiopericytomas, while epithelioid leiomyosarcomas, fibrosarcomas, malignant schwannomas, and synovial sarcomas were negative or only weakly positive. Our results demonstrate that, while smooth muscle myosin is a very good marker of normal smooth muscle and benign smooth muscle tumors, it is expressed in diagnostically significant amounts in less than a third of spindle-cell leiomyosarcomas and none of the studied epithelioid leiomyosarcomas.

Hydrocortisone and isoproterenol effects on trachealis cAMP and relaxation

Isoproterenol concentration-response curves for cAMP formation and relaxation were determined in control and hydrocortisone-treated strips of canine tracheal smooth muscle. Adenosine 3'5'-cyclic monophosphate(cAMP) formation and muscle relaxation were well correlated, and both responses were enhanced proportionally by hydrocortisone treatment. Guanosine 3'5'-cyclic monophosphate was unchanged by isoproterenol but was increased to a small but significant extent by hydrocortisone. Prostaglandin E2 (not a beta-adrenergic agonist) relaxed the muscle strips, but this effect was not enhanced by hydrocortisone pretreatment. Our data are compatible with the concept that cAMP is an obligatory intermediate in the chain of events by which beta-adrenergic agonists relax airway smooth muscle. The action of hydrocortisone on this process is localized at or before cAMP formation, since it enhanced both cAMP formation and relaxation to the same extent.

[Cells containing smooth-muscle myosin during healing of myocardial infarction in rats]

Immunoperoxidase and autoradiographic techniques were used to examine smooth muscle myosin-containing cells in the injured zone during rat myocardial infarction healing. It was discovered that smooth muscle myosin-containing cells occurred on the 3d day of myocardial infarction and persisted during four months of experiment. The relative volume of the cells did not exceed 5% of the total tissue volume in the injured zone. The number of these cells in the subendocardial area was greater than that in the center of the infarction area throughout all the stages of experiment. Only a few smooth muscle myosin-containing cells included 3H-thymidine, which points to a weak proliferative activity of these cells.

Isolation, purification and characterization of the intermediate filament protein desmin from porcine smooth muscle

Desmin was isolated from porcine stomach smooth muscle, which had been treated with 0.6 M KCl in the presence of Triton X-100, by extraction with 6 M urea and chromatographed on CM-Sepharose CL-6B at pH 5. After delipidation with chloroform-methanol, the protein was purified by affinity chromatography on arginine methylester Sepharose 4B and single-stranded DNA-cellulose, respectively. Chromatography on single-stranded DNA-cellulose removed a considerable amount of vimentin which had been extracted and enriched together with desmin. The molecular weight of the purified desmin was 55,000 as determined by polyacrylamide gradient slab gel electrophoresis in the presence of Na-dodecylsulfate. Two-dimensional polyacrylamide gel electrophoresis revealed one major polypeptide of pI 5.3 to 5.4 accompanied by two to three acidic, isoelectric variants. During incubation in the presence of 150 mM KCl, desmin assembled into 10 nm filaments. This method allows the isolation of large amounts of pure desmin in a relatively short time with only minimal denaturation of the protein.

Phosphorus-31 NMR studies of smooth muscle from guinea-pig taenia coli

Phosphorus-31 NMR spectra of superfused isometrically mounted guinea-pig taenia coli were obtained using a horizontal probe at 103.2 MHz. The spectra showed resonances for ATP, phosphocreatine (PCr), and a sugar phosphate resonance. The PCr/ATP ratio was between 1.5 and 2.0 consistent with chemical analysis of tissue extracts. The level of PCr, but not of ATP, decreases reversibly during contraction or inhibition of respiration. These conditions did not cause substantial changes in the intracellular pH, which was 7.0 +/- 0.1.

Photoaffinity labeling of P2-purinergic and H1-histamine receptors in intact smooth muscle

This paper discusses the general applicability of photoaffinity labels as pharmacological receptor antagonists in functional studies of intact smooth muscle preparations. Guidelines are suggested that take into account the criteria for photoaffinity labeling studies as well as those for use with conventional antagonists.

Structure of myosin/paramyosin filaments from a molluscan smooth muscle

Small-angle X-ray diffraction patterns of chemically skinned pedal retractor muscles from Mytilus (PRM) in the relaxed state show a set of diffuse off-meridional reflections that arise from a helical array of myosin crossbridges with 8/3 screw symmetry. Experiments involving extraction of myosin as well as analysis of the rigor pattern have been used to confirm the origin of these reflections. The relatively high myosin/paramyosin molar ratio (1.3 to 1.6) in PRM compared to other molluscan smooth muscles may account for the observation of the relatively stronger diffraction from the myosin array. Thick filaments isolated from PRM and contrasted by negative staining for electron microscopy appear to be very long (up to 17 micron), and to have a rather small diameter (about 40 nm at the center); they taper gradually toward the ends. These filaments show a clear transverse band pattern repeating at 14.4 nm and elongated projections (crossbridges) at the surface except in the central bare zone. Optical diffraction patterns show reflections from crossbridges consistent with the X-ray patterns of the relaxed whole muscle. Filaments unidirectionally shadowed with platinum show diagonal striations running at an angle of about 17 degrees to the filament axis, revealing that the crossbridges are arrayed in a right-handed helix. The paramyosin core is clearly seen upon extraction of myosin. Observations on both negatively stained and sectioned material are consistent with the results of Elliott (1979) and Bennett & Elliott (1981) suggesting a layered structure of the core. Cores stripped of myosin, however, appear to undergo some distortion indicating that the three-dimensional structure is not yet completely solved. The assembly of these thick filaments presents intriguing structural problems since the myosin surface lattice does not appear to have the same symmetry as the underlying paramyosin core.

The C-proteins of rabbit red, white, and cardiac muscles

C-proteins have been isolated from rabbit red skeletal muscle (soleus and semitendinosus) and cardiac muscle and their structure and properties compared with those of white muscle C-protein. The Mr of white, red, and cardiac C-proteins are 135,000, 145,000, and 150,000, respectively, and their s20,w values are 4.3, 3.8, and 4.8 S, indicating that red C-protein is more asymmetric than the other two. They elute quite differently from hydroxylapatite columns. Two-dimensional CNBr peptide maps show extensive differences in primary structure, and anti-white C-protein does not precipitate red or cardiac C-protein. Despite these structural differences, all three C-proteins bind equally to white, red, or cardiac myosin and to actin. All three have the same effects on actomyosin ATPase in 50 mM KCl; they inhibit red and white skeletal actomyosins but slightly activate cardiac actomyosin. X-protein, a 140,000-dalton contaminant of white C-protein, was also investigated. It is very similar to red C-protein in elution from hydroxylapatite columns, S20,w, amino acid composition, and primary structure, but small differences in Mr and peptide maps indicate that the two proteins are probably not identical.

Autoradiographic localization of autonomic receptors in airway smooth muscle. Marked differences between large and small airways

Autoradiographic methods were used to determine the distribution of autonomic receptors in airway smooth muscle of ferret from trachea to terminal bronchioles; [3H]dihydroalprenolol, [3H]prazosin, and [3H]quinuclidinyl benzilate were used to label beta-adrenergic, alpha-adrenergic, and muscarinic receptors, respectively, using experimental conditions that gave maximal specific receptor binding. Marked differences were found in the longitudinal distribution of each receptor and in distribution of the various receptors in each caliber airway. Beta-receptors were present in high density throughout the airways, with the highest density in bronchioles. Alpha-receptors were sparse in large airways, but numerous in small bronchioles, whereas cholinergic receptors were numerous in bronchial smooth muscle, sparse in proximal bronchioles, and almost absent from distal bronchioles. This method may be useful in studying alterations of autonomic receptors distribution in small and large airways after experimental manipulation and in disease.

Lack of vasoactive intestinal polypeptide nerves in esophageal achalasia

Vasoactive intestinal polypeptide-containing nerves were examined in the lower esophagus of control and achalasia patients. The smooth muscle in patients with achalasia had conspicuously fewer vasoactive intestinal polypeptide-immunoreactive nerve fibers than specimens from control patients. Also the concentration of vasoactive intestinal polypeptide in the lower esophagus was much reduced in achalasia. In view of the potent smooth muscle relaxing effects of vasoactive intestinal polypeptide, it is suggested that the reduced number of vasoactive intestinal polypeptide fibers in the achalasic esophagus causes or at least contributes to the incomplete relaxation and the increased resting tone of the lower esophageal sphincter characteristic of this disease.

Studies on the effect of phosphorylation of the 20,000 Mr light chain of vertebrate smooth muscle myosin

Myosin was rapidly prepared from turkey gizzard muscle to a high level of purity, in high yield and in a non-phosphorylated state. It was consistently observed that the actin-activated Mg2+ ATPase activity of this myosin was dependent on the level of phosphorylation of the 20,000 Mr light chain, for example, in the non-phosphorylated state, the myosin Mg2+ ATPase activity was not activated by actin whereas, when the light chains were phosphorylated, the Mg2+ ATPase activity of the myosin was activated approximately ninefold by actin. Using the "desensitized" scallop myosin test system (Kendrick-Jones et al., 1976; Sellers et al., 1980) it was further demonstrated that phosphorylation of the 20,000 Mr gizzard light chain has a regulatory role. These results also suggest that the regulatory mechanisms mediated by smooth muscle myosin light chains and molluscan myosin regulatory light chains are similar, i.e. in the absence of Ca2+, both types of light chain inhibit myosin interaction with actin and this inhibition is relieved by either phosphorylation in smooth muscle or by direct calcium binding in molluscan myosins. The basis of regulation exerted by these light chains is therefore repression derepression. Using a variety of techniques, i.e. turbidity measurements, quantitative high speed centrifugation, electron microscopy and dark field light microscopy, it was observed that the stability of gizzard myosin filaments at approximately physiological conditions (0.15 M-NaCl, 1 mM-MgATP, pH 7.0) was dependent on the level of light chain phosphorylation. Using purified calmodulin-dependent light chain kinase and phosphatase, it was further shown that these gizzard myosin filaments can be reversibly assembled and disassembled as a result of phosphorylation-dephosphorylation of the 20,000 Mr light chain.

Distribution of alpha-actinin in single isolated smooth muscle cells

In order to probe the organization of the contractile machinery in smooth muscle, we have studied the distribution of alpha-actinin, a protein present in high concentration in dense bodies, structures apparently analogous to the Z-disks of striated muscle. Localization of alpha-actinin in single isolated smooth muscle cells of the stomach muscularis of Bufo marinus was determined by analysis of the pattern of anti-alpha-actinin staining in single fluorescence photomicrographs, stereo pair micrographs, and computerized three-dimensional reconstructions from multiple image planes. The distribution of anti-alpha-actinin and antitubulin staining was compared in contracted and relaxed cells. The studies revealed that alpha-actinin is present in high concentrations in fusiform elements (mean axial ratio = 4.82) throughout the cytoplasm and in larger, more irregularly shaped plaques along the cell margins. Many of the fusiform-stained elements are organized into stringlike arrays characterized by a regular repeating pattern (mean center-to-center interspace = 2.2 +/- 0.1 micron). These linear arrays appear to terminate at the anti-alpha-actinin stained larger plaques along the cell margin; several of these strings often run in parallel with their elements in lateral register. While this general pattern of organization is maintained in cells during contraction, the distance between successive stained elements in stringlike arrays is decreased. We suggest that the decrease in the distance between elements in these strings results from shortening of materials that constitute these linear arrays. We do not believe that the shortening within these arrays reflects compression by forces generated elsewhere within the cell, as the reorganization of noncontractile microtubules is qualitatively different from the changes in the pattern of anti-alpha-actinin staining.

Distribution of histamine receptors in isolated canine airways

The distribution of histamine receptors was examined in isolated trachealis smooth muscle strips and helical strips of large (5 mm) and small (1.5 mm) intrapulmonary airways. All airways contracted in response to histamine, but the sensitivity to this agent was significantly greater in intrapulmonary airways than in trachealis strips. A dose-dependent tachyphylaxis to histamine occurred when airways were exposed repeatedly to 10(-4) M histamine but not to 5 X 10(-6) M histamine. The H1-agonist, 2-methylhistamine, also caused airway contractions, although they were less forceful than those caused by histamine. Both histamine- and 2-methylhistamine-induced contractions were blocked by the H1-antagonist, pyrilamine. The H2-agonists, 4-methylhistamine and dimaprit, as well as histamine in the presence of pyrilamine failed to relax both acetylcholine- and 5-hydroxytryptamine-induced contractions. Moreover, the H2-antagonist, metiamide, had no effect on histamine-induced contractions. We conclude that histamine H1-receptors are present in both extrapulmonary and intrapulmonary airways of the dog and cause contraction when stimulated. In contrast, histamine H2-receptor activity could not be demonstrated in the airways of this species.

Purification of the intermediate filament-associated protein, synemin, from chicken smooth muscle. Studies on its physicochemical properties, interaction with desmin, and phosphorylation

Synemin, a 230,000-dalton protein associated with desmin- and vimentin-containing intermediate filaments (Granger, B. L., and Lazarides, E. (1980) Cell 22, 727-738), has been purified from gizzard smooth muscle and biochemically characterized. Purification was achieved by extracting the salt-insoluble pellet of muscle protein with 6 M urea and chromatography of the urea extract on columns of hydroxylapatite, DEAE-Sephacel, and phosphocellulose. The soluble form of synemin is a globular tetramer of 980,000 daltons with a S20,w of 22.4 +/- 3.2. Synemin has a pI of 5.34, in agreement with its high content in glutamic acid (20%), and is rich in serine (11%) and poor in cysteine (0.4%). Synemin is phosphorylated in smooth muscle and is one of the muscle proteins with the highest capacity to incorporate exogenously added [32P]phosphate. Of the [32P] phosphate incorporated into synemin, 95% is bound to serine and only 5% to threonine. The phosphorylation of synemin is enhanced by the cyclic AMP analog, 8-Br-cyclic AMP. Immunofluorescence studies using anti-synemin antibodies show that purified synemin binds to filaments of desmin assembled in vitro. Synemin specifically inhibits the immunoprecipitation of purified soluble desmin by anti-desmin antibodies, indicating that synemin interacts in vitro with soluble desmin.

Purine receptors in the rat anococcygeus muscle

Adenosine triphosphate (ATP) caused contraction of the resting isolated rat anococcygeus muscle. Non-phosphorylated purines did not cause contraction of the resting muscle but did so in muscles in which the tone was raised by carbachol or guanethidine. Adenosine, (-)N6-phenylisopropyladenosine (PIA) and 5'-N-ethyl-carboxamide adenosine (NECA) were approximately equipotent, and these responses were not prevented by theophylline, quinidine, 2,2'-pyridylisatogen tosylate, phentolamine, methysergide, dipyridamole, hexobendine or indomethacin. The contractions became smaller as muscle tone progressively declined, and it is suggested that this effect may explain the apparent blockade of ATP responses by indomethacin reported previously. Adenosine, 2-chloroadenosine, ATP, PIA and NECA inhibited contractile responses of the anococcygeus to field stimulation of the excitatory adrenergic innervation. This inhibitory action was blocked by theophylline, and as PIA was easily the most potent purine tested, it may involve activation of an A1/Ri receptor. It is also argued, however, that the A/R scheme of classification may be inappropriate for the description of responses of intact tissues. As response to noradrenaline were not changed by the purines, the inhibitory effect on stimulation-evoked contractions is probably mediated at a presynaptic site. None of the purines tested had any effect on the neurally mediated inhibition of the anococcygeus which is seen when intrinsic tone is raised and the excitatory adrenergic nerves are blocked.

Ordered phosphorylation of the two 20 000 molecular weight light chains of smooth muscle myosin

The time courses of phosphorylation of the Mr 20 000 light chains by purified myosin light chain kinase plus calmodulin were determined. In confirmation of an earlier report [Persechini, A., & Hartshorne, D. J. (1981) Science (Washington, D.C.) 213, 1383-1385], a steady-state kinetic analysis indicates that the phosphorylation occurs in an ordered manner; i.e., at a phosphorylation level of 0.5 mol of 32P incorporated per mol of bound Mr 20 000 light chain, each myosin molecule would have one phosphorylated head. The kinetic parameters obtained for the phosphorylation of the more reactive myosin head are similar to those determined by using isolated light chains. It is suggested that the ordered, or sequential, phosphorylation, and the different reactivities of the two Mr 20 000 light chains, is the result of preexisting asymmetry of the myosin molecule. Similar patterns of myosin phosphorylation are obtained in both the absence and presence of skeletal muscle actin.

Actin in the extracellular matrix of smooth muscle cells. An immunoelectron microscopic study

Actin has been specifically detected in the intercellular matrix of mouse smooth muscle cells and along the vascular internal elastic membrane by means of immunoferritin-electron microscopy, employing human antibodies to smooth muscle actin. The presence of actin in the smooth muscle matrix suggests that this protein may have relevance in controlling cell-to-cell adhesion and the sliding of one smooth muscle cell over the other, both in contracted and expanded status. The association of actin with the elastic membrane may represent the anatomical basis of a functional link between elastic membrane, adjacent fibronectin and smooth muscle cells. Thus the transmission of movement from the smooth muscle cells to the elastic membrane can be achieved.