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Cooke PH, Fay FS, Craig R. Myosin filaments isolated from skinned amphibian smooth muscle cells are side-polar. J Muscle Res Cell Motil 1989; 10:206-20. [PMID: 2503537 DOI: 10.1007/bf01739811] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The structure of myosin filaments isolated from skinned toad stomach smooth muscle cells has been examined by electron microscopy as a step toward identifying the in vivo structure. When negatively stained following exposure to relaxing conditions, the filaments exhibited a continuous 14-nm axial repeat of crossbridge projections with no central bare zone. The filaments thus differed from the bipolar filaments found in striated muscle and displayed instead features resembling side-polar and mixed-polarity filament models. By rotation of isolated filaments around their longitudinal axes it was found that cross bridges occurred only along two sides of the filament, an arrangement consistent with the side-polar but not the mixed-polarity model. The polarity is thus similar to that proposed for ribbons (Small & Squire, J. molec. Biol. 67, (1972) 17-149) and for synthetic smooth muscle myosin filaments (Craig and Megerman, J. Cell Biol. 75, (1977) 990-996); their appearance in cross-section, however, shows that these structures are filaments (i.e. with two axes of similar dimensions) and not broad ribbons. As the filaments were derived directly from skinned cells which contracted and relaxed in response to physiological levels of MgATP and Ca2+ at rates comparable to those of native, isolated cells, this unusual arrangement of cross bridges appears to be an effective, functional form of myosin in the contractile apparatus. Side-polar filaments therefore merit consideration as plausible candidates for the native organization of myosin in vertebrate smooth muscle cells.
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Affiliation(s)
- P H Cooke
- Department of Cell Biology, University of Massachusetts Medical School, Worcester 01655
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Asghar A, Samejima K, Yasui T. Functionality of muscle proteins in gelation mechanisms of structured meat products. Crit Rev Food Sci Nutr 1985; 22:27-106. [PMID: 3899516 DOI: 10.1080/10408398509527408] [Citation(s) in RCA: 210] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Recent advances in muscle biology concerning the discoveries of a large variety of proteins have been described in this review. The existence of polymorphism in several muscle proteins is now well established. Various isoforms of myosin not only account for the difference in physiological functions and biochemical activity of different fiber types or muscles, but also seem to differ in functional properties in food systems. The functionality of various muscle proteins, especially myosin and actin in the gelation process in modal systems which simulate structured meat products, is discussed at length. Besides, the role of different subunits and subfragments of myosin molecule in the gelation mechanism, and the various factors affecting heat-induced gelation of actomyosin in modal systems are also highlighted. Finally, the areas which need further investigation in this discipline have been suggested.
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Kendrick-Jones J, Cande WZ, Tooth PJ, Smith RC, Scholey JM. Studies on the effect of phosphorylation of the 20,000 Mr light chain of vertebrate smooth muscle myosin. J Mol Biol 1983; 165:139-62. [PMID: 6133003 DOI: 10.1016/s0022-2836(83)80247-2] [Citation(s) in RCA: 59] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
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.
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Taylor MJ. The role of pH and buffer capacity in the recovery of function of smooth muscle cooled to -13 degrees C in unfrozen media. Cryobiology 1982; 19:585-601. [PMID: 7151457 DOI: 10.1016/0011-2240(82)90188-2] [Citation(s) in RCA: 34] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
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Koretz JF, Coluccio LM, Bertasso AM. The aggregation characteristics of column-purified rabbit skeletal myosin in the presence and absence of C-protein at pH 7.0. Biophys J 1982; 37:433-40. [PMID: 6895856 PMCID: PMC1328825 DOI: 10.1016/s0006-3495(82)84689-4] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
The aggregation properties of column-purified rabbit skeletal myosin at pH 7.0 were investigated as functions of ionic strength, protein concentration, and time. Filaments prepared by dialysis exhibited the same average length and population distribution at 0.10 and 0.15 M KCl at protein concentrations greater than 0.10 mg/ml; similar results were obtained at .0.20 M KCl, although average filament length was approximately 0.5 micrometer shorter. Once formed, these length distributions remained virtually unchanged over an 8-d period. At and below 0.10 mg/ml, average filament length decreased as a function of protein concentration; filaments prepared from an initial concentration of 0.02 mg/ml were half the length of those prepared at 0.2 mg/ml. Filaments prepared by dilution exhibited a sharp increase in average length as the time-course increased up to 40 s, then altered only slightly over a further period of 4 min. Addition of C-protein in a molar ratio of 1-3.3 myosin molecules affected most of these results. Average filament length was affected neither by ionic strength nor by initial protein concentration down to 0.04 mg/ml or over an 8-d period. Filaments formed by dilution in the presence of C-protein exhibited a constant average length and hypersharp length distribution over variable time courses up to 7 min. It is possible that C-protein acts to stabilize the antiparallel intermediate during filamentogenesis, and may also affect subunit addition to this nucleus.
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Mackenzie JM, Epstein HF. Paramyosin is necessary for determination of nematode thick filament length in vivo. Cell 1980; 22:747-55. [PMID: 7193096 DOI: 10.1016/0092-8674(80)90551-6] [Citation(s) in RCA: 66] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
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Taylor DL, Condeelis JS. Cytoplasmic structure and contractility in amoeboid cells. INTERNATIONAL REVIEW OF CYTOLOGY 1979; 56:57-144. [PMID: 37189 DOI: 10.1016/s0074-7696(08)61821-5] [Citation(s) in RCA: 285] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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Zobel CR. Proteolytic fragments from the lobster myosin molecule. BIOCHIMICA ET BIOPHYSICA ACTA 1978; 536:142-55. [PMID: 708757 DOI: 10.1016/0005-2795(78)90060-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The fragments produced by proteolysis of lobster abdominal muscle myosin with trypsin, alpha-chymotrypsin and papain have been investigated by sodium dodecyl sulfate (SDS) gel electrophoresis. Essentially monodisperse populations of long rods are produced by alpha-chymotryptic and papain digestion of rabbit myosin but corresponding digestion of lobster myosin yields multicomponent species. Similarly the low ionic strength insoluble fraction from tryptic digestion of lobster myosin is polydisperse in contrast to essentially monodisperse light meromyosin from rabbit myosin. Comparative tryptic digestion of rabbit and lobster myosin papain long rods shows that the latter have five susceptible cleavage sites in the subfragment-2 region while rabbit long rods have only one: both long rods appear to have three cleavage sites in the light meromyosin region. The fragments produced by tryptic digestion of rabbit myosin papain long rods have been tentatively identified by comparison with fragments isolated from papain digests of rabbit heavy meromyosin and tryptic digests of rabbit light meromyosin. The results suggest differences in sensitivity to enzymic proteolysis between the subfragment-2 regions in rabbit and lobster myosin as well as relative differences in proteolytic sensitivity between the subfragment-2 and light meromyosin region within the individual molecules. Partial explanation of the observation is proposed on the basis of differences in heavy chain compositions.
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Hinssen H, D'Haese J, Small JV, Sobieszek A. Mode of filament assembly of myosins from muscle and nonmuscle cells. JOURNAL OF ULTRASTRUCTURE RESEARCH 1978; 64:282-302. [PMID: 712882 DOI: 10.1016/s0022-5320(78)90037-0] [Citation(s) in RCA: 82] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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Abstract
There are three classes of myofilaments in vertebrate smooth muscle fibers. The thin filaments correspond to actin and the thick filaments are identified with myosin. The third class of myofilaments (100 A diam) is distinguished from both the actin and the myosin on the basis of fine structure, solubility, and pattern of localization in the muscle fibers. Direct structural evidence is presented to show that the 100A filament constitute an integrated filamentous network with the dense bodies in the sarcoplasm, and that they are not connected to either the actin or myosin filaments. Examination of (a) isolated dense bodies, (b) series of consecutive sections through the dense bodies, and (c) redistributed dense bodies in stretched muscle fibers supports this conclusion. It follows that the 100-A filaments complexes constitute a structrally distinct filamentous network. Analysis of polyacrylamide gels after electrophoresis of cell fractions that are enriched with respect to the 100-A filaments shows the presence of a new muscle protein with a molecular weight of 55,000. This protein can form filamentous segments that closely resemble in structure the native, isolated 100-A filaments. The results indicate that the filamentous network has a structure and composition that distinguish it from the actin and myosin in vertebrate smooth muscle.
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Siemankowski RF, Zobel CR. Comparative studies on the structure and aggregative properties of the myosin molecule. III. The in vitro aggregative properties of the lobster myosin molecule. BIOCHIMICA ET BIOPHYSICA ACTA 1976; 420:406-16. [PMID: 3216 DOI: 10.1016/0005-2795(76)90332-9] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The solubility of rabbit skeletal and lobster abdominal muscle myosin has been studied in monovalent salt solutions as a function of pH (over the range 4.75 to 8.5) and ionic strength (50-500 mM). Rabbit skeletal muscle myosin was found to precipitate over a narrower pH range than the lobster abdominal muscle myosin but at equivalent pH values and ionic strengths the former exhibited greater solubility. Comparison of the solubility of rabbit myosin, per se with that of light meromyosin and lobster myosin with its equivalent proteolytically produced fragment (fraction B1) showed that both rod fragments were more soluble than their parent molecules. Under conditions of low solubility (low ionic strength and pH) the quantitiy of protein in solution remained essentially constant with increasing total protein, thus suggesting that the aggregation phenomenon is of a phase transition type. Examination of the aggregates by electron microscopy revealed that rabbit myosin formed classical, elongate, spindle-shaped filaments similar to those previously observed by others. In contrast lobster myosin only formed short, dumbbell-shaped filaments 0.2-0.3 mum long. Consideration of the pH ranges over which aggregation occurred suggests that protonation of histidine residues may be involved in rabbit myosin filament formation while for lobster myosin, aggregation may involve protonation of epsilon-amino or guanidino groups. The possible relationship between the distribution of these groups along the rod portion of the myosin molecule and the formation of elongate filaments has been explored.
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Shoenberg CF, Needham DM. A study of the mechanism of contraction in vertebrate smooth muscle. Biol Rev Camb Philos Soc 1976; 51:53-104. [PMID: 3230 DOI: 10.1111/j.1469-185x.1976.tb01120.x] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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Ashton FT, Somlyo AV, Somlyo AP. The contractile apparatus of vascular smooth muscle: intermediate high voltage stereo electron microscopy. J Mol Biol 1975; 98:17-29. [PMID: 1195377 DOI: 10.1016/s0022-2836(75)80098-2] [Citation(s) in RCA: 171] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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Pollard TD. Electron microscopy of synthetic myosin filaments. Evidence for cross-bridge. Flexibility and copolymer formation. J Cell Biol 1975; 67:93-104. [PMID: 1236853 PMCID: PMC2109586 DOI: 10.1083/jcb.67.1.93] [Citation(s) in RCA: 69] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Electron micrographs of negatively stained synthetic myosin filaments reveal that surface projections, believed to be the heads of the constituent myosin molecules, can exist in two configurations. Some filaments have the projections disposed close to the filament backbone. Other filaments have all of their projections widely spread, tethered to the backbone by slender threads. Filaments formed from the myosins of skeletal muscle, smooth muscle, and platelets each have distinctive features, particularly their lengths. Soluble mixtures of skeletal muscle myosin with either smooth muscle myosin or platelet myosin were dialyzed against 0.1 M KC1 at pH 7 to determine whether the simultaneous presence of two types of myosin would influence the properties of the filaments formed. In every case, a single population of filaments formed from the mixtures. The resulting filaments are thought to be copolymers of the two types of myosin, for several reasons: (a) their length-frequency distribution is unimodal and differs from that predicted for a simple mixture of two types of myosin filaments; (b) their mean length is intermediate between the mean lengths of the filaments formed separately from the two myosins in the mixture; (c) each of the filaments has structural features characteristic of both of the myosins in the mixture; and (d) their size and shape are determined by the proportion of the two myosins in the mixture.
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Abstract
Smooth muscle cells of the mouse vas deferens fixed with 5% glutaraldehyde contained three types of filaments, namely, thin (50-80) A) filaments, intermediate (100 A) filaments and thick (120-180 A) filments. However, in 2 out of 16 experiments, under identical conditions, the cells did not contain thick filaments. With OSO4 fixation, thin filaments were not prominent, the most obvious being thick (120-250 A) and intermediate (100 A) filaments. After soaking in a modified Ringer solution under no applied tension for one hour, thick filaments (120-180 A) appeared prominently in smooth muscle cells of the mouse vas deferens and thin filaments were in ordered bundles. By 4 hours, thick filaments had increased in size and density, with thin filaments distributed randomly around them. After 8 hours in Ringer, thin filaments were diffuse and difficult to discern, while thick filaments were large (up to 300 A) and electron-dense. Intermediate (100 A) filaments were present in association with dark bodies. Physiological experiments indicated that the intracellular components responsible for the development of a mechanical response were still functional at this time. The presence of "thick filaments" is also reported in degenerating smooth muscle cells of the guinea-pig vas deferens in tissue culture.
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Pollard TD, Weihing RR. Actin and myosin and cell movement. CRC CRITICAL REVIEWS IN BIOCHEMISTRY 1974; 2:1-65. [PMID: 4273099 DOI: 10.3109/10409237409105443] [Citation(s) in RCA: 684] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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Bois RM. The organization of the contractile apparatus of vertebrate smooth muscle. Anat Rec (Hoboken) 1973; 177:61-77. [PMID: 4747741 DOI: 10.1002/ar.1091770107] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
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Elford BC, Walter CA. Effects of electrolyte composition and pH on the structure and function of smooth muscle cooled to -79 degrees C in unfrozen media. Cryobiology 1972; 9:82-100. [PMID: 5035150 DOI: 10.1016/0011-2240(72)90015-6] [Citation(s) in RCA: 73] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
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Zucker-Franklin D, Grusky G. The actin and myosin filaments of human and bovine blood platelets. J Clin Invest 1972; 51:419-30. [PMID: 4333023 PMCID: PMC302141 DOI: 10.1172/jci106828] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
The contractility of platelets has been attributed to an actomyosin-like protein which has been well defined on a physicochemical basis. Moreover, platelets contain +/-80 A filaments which resemble actin filaments in smooth muscle. Studies were undertaken on human and bovine platelets to better define the morphologic structures which may subserve this contractile function. In order to identify actin, the ability of the filaments to react with heavy meromyosin (HMM) was tested. Accordingly, platelets were glycerinated and treated with HMM. In addition, platelet actin was extracted, reacted with HMM, and examined by negative staining. In both instances typical arrowhead structures with clearly defined polarity and a periodicity of +/-360 A formed. As is the case with purified muscle actin, the complexes were dissociable with Mg-ATP. The formation of myosin-like filaments was observed when osmotically shocked platelets were incubated with MgCl(2) and excess ATP. These "thick" filaments measured 250-300 A in width, tapered at both ends and often occurred in clumps. They resembled aggregates of thick filaments described in contracted smooth muscle. Extraction of platelets by methods suitable for the demonstration of myosin showed filaments with an average length of 0.3 mu, a smooth shaft, and frayed or bulbous ends. These appeared identical to those seen in synthetically prepared myosin of striated muscle. It is suggested that the filaments described here represent the actin and myosin of platelets.
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Rostgaard J. Electron microscopy of filaments in the basal part of rat kidney tubule cells, and their in situ interaction with heavy meromyosin. ZEITSCHRIFT FUR ZELLFORSCHUNG UND MIKROSKOPISCHE ANATOMIE (VIENNA, AUSTRIA : 1948) 1972; 132:497-521. [PMID: 4344793 DOI: 10.1007/bf00306638] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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Hayes D, Huang M, Zobel CR. Electron microscope observations on thick filaments in striated muscle from the lobster Homarus americanus. JOURNAL OF ULTRASTRUCTURE RESEARCH 1971; 37:17-30. [PMID: 4939639 DOI: 10.1016/s0022-5320(71)80037-0] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
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Abstract
Two sets of myofilaments were demonstrated after incubation of strips of rabbit portal-anterior mesenteric vein under moderate stretch in a physiological salt solution. Thick filaments had a mean diameter of 18 nm and reached a maximum length of 1.4 microm with a mean length of 0.61 microm. In transverse sections, 2.5-5 nm particles were resolved as subunits of the thick filaments. Thin filaments had an average diameter of 8.4 nm and generally conformed to the structure believed to represent actin filaments in smooth and striated muscles. In the areas of maximum concentration there were 160-328 thick filaments/microm(2) and the lowest ratio of thin to thick filaments was 12:1. Thick filaments were present in approximately equal numbers in vascular smooth muscle relaxed by theophylline, in Ca(++)-free solution, or contracted by norepinephrine. The same preparatory procedures used with vascular smooth muscle also enabled us to visualize thick filaments in guinea pig and rabbit taenia coli and vas deferens.
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Cooke PH, Chase RH. Potassium chloride-insoluble myofilaments in vertebrate smooth muscle cells. Exp Cell Res 1971; 66:417-25. [PMID: 4104114 DOI: 10.1016/0014-4827(71)90696-3] [Citation(s) in RCA: 59] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
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Abstract
Segments of the lower small intestine of the toad Bufo marinus were excised and soaked for approximately 2 hr in Ringer's solution (pH 7.4 or 7.8) containing crystalline trypsin and then fixed for electron microscopy at approximately the same pH. Thin sections of the tunica muscularis of these specimens show smooth muscle cells ranging in appearance from severely damaged at one extreme to apparently unaffected at the other. Among these are cells at intermediate stages, including some which exhibit large and conspicuous populations of thick filaments closely resembling artificially prepared aggregates of smooth muscle myosin. The thick filaments have the form of tactoids approximately 250-300 A in diameter in their middle regions and are approximately 0.5-1.0 micro in length. In some preparations they also display an axial periodicity approximating 143 A. They are usually randomly oriented and segregated from the thin filaments, which tend to form closely packed, virtually crystalline bundles at the periphery of these cells. "Dense bodies" are absent from cells showing these changes. The simplest interpretation of these data is that smooth muscle myosin normally exists among the actin filaments in a relatively disaggregated state and that trypsin induces aggregation by altering the conformation of the myosin molecule. Alternatively, trypsin may act indirectly through an effect on some other smooth muscle protein which normally forms a stable complex with relatively disaggregated myosin.
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Rice RV, Moses JA, McManus GM, Brady AC, Blasik LM. The organization of contractile filaments in a mammalian smooth muscle. J Cell Biol 1970; 47:183-96. [PMID: 4327514 PMCID: PMC2108389 DOI: 10.1083/jcb.47.1.183] [Citation(s) in RCA: 77] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Ordered arrays of thin filaments (65 A diameter) along with other apparently random arrangements of thin and thick filaments (100-200 A diameter) are observed in contracted guinea pig taenia coli rapidly fixed in glutaraldehyde. The thin-filament arrays vary from a few to more than 100 filaments in each array. The arrays are scattered among isolated thin and thick filaments. Some arrays are regular such as hexagonal; other arrays tend to be circular. However, few examples of rosettes with regular arrangements of thin filaments surrounding thick filaments are seen. Optical transforms of electron micrographs of thin-filament arrays give a nearest-neighbor spacing of the thin filaments in agreement with the "actin" filament spacing from x-ray diffraction experiments. Many thick filaments are closely associated with thin-filament arrays. Some thick filaments are hollow circles, although triangular shapes are also found. Thin-filament arrays and thick filaments extend into the cell for distances of at least a micron. Partially relaxed taenia coli shows thin-filament arrays but few thick filaments. The suggestion that thick filaments aggregate prior to contraction and disaggregate during relaxation is promoted by these observations. The results suggest that a sliding filament mechanism operates in smooth muscle as well as in striated muscle.
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Elliott GF, Rome EM, Spencer M. A type of contraction hypothesis applicable to all muscles. Nature 1970; 226:417-20. [PMID: 4245372 DOI: 10.1038/226417a0] [Citation(s) in RCA: 51] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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Cooke PH, Chase RH, Cortés JM. Thick filaments resembling myosin in electrophoretically-extracted vertebrate smooth muscle. Exp Cell Res 1970; 60:237-46. [PMID: 5424316 DOI: 10.1016/0014-4827(70)90510-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
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