William C. Ullrick

Effects of halothane on isometric contractions of isolated heart muscle.

In isometric contractions of an isolated heart muscle preparation exposed to halothane (0.10, 0.40, 0.85, 1.05 and 2.35 volumes per cent), peak developed tension and maximum rate of tension development were reduced as much as 53 per cent and 57 per cent, respectively, in direct proportion to the concentration of the anesthetic. Time to peak tension and total twitch duration were not decreased more than 6.3 per cent by any concentration of halothane. Resting tension was affected only by the highest concentration, 2.35 volumes per cent, which lowered it 6.8 per cent Relaxation time and muscle length were not altered. Recovery from the effect of halothane was essentially complete in each instance. The results are consistent with the concept that halothane exerts its cardiac effects primarily by a direct reduction in active state intensity of heart muscle.

Purification and properties of the isolated honeybee Z-disc

Abstract Z-discs have been isolated from honeybee indirect flight muscle fibers with 0.43% lactic acid, and have been purified with differential and sucrose density-gradient centrifugation. In the light microscope, isolated Z-discs are pale, round, homogeneous structures with diameters ranging from 2 μm to 9 μm, depending on the nature of the suspending medium. In the electron microscope, small Z-discs (2 μm in diameter) examined on Formvar-coated grids are thick, dense and lacking in detail; swollen Z-discs (6 μm in diameter) have a reticular pattern with 3-fold symmetry. Sectioned isolated Z-discs show fine projections extending about 1300 A from both surfaces. These projections may represent insoluble stubs of thin filaments or “C” filaments, which connect thick filaments to the Z-band. Although honeybee isolated Z-discs are very resistant structures that remain insoluble in a number of protein solvents and in solutions reported to extract Z-band material from vertebrate fibrils, it has been possible to solubilize them in 7 m -guanidine-HCl, 2.5 m m -dithiothreitol, 2.5 m m -EDTA (pH 7.5), and to resolve their components electrophoretically. Sodium dodecyl sulfate gel electrophoresis studies indicate that there are at least four polypeptides, with molecular weights of 87,000, 113,000, 158,000, and 175,000, localized in the isolated Z-disc. The Z-disc backbone contains no significant quantity of lipid as earlier reports have suggested. Total lipid extracted from Z-disc preparations with chloroform/ methanol comprises less than 1% of the Z-disc protein.

Are there extensions of thick filaments to the Z line in vertebrate and invertebrate striated muscle

The experiments conducted were designed to determine the presence or absence of extensions of the thick, myosin-containing filaments to the Z lines in vertebrate and invertebrate muscle. Traditionally these possible extensions have been referred to as “connecting” filaments; more recently (in vertebrate muscle) as “gap” filaments. We performed serial cross sections of stretched frog sartorius and chameleon tongue muscles, and of flight muscles of the Belostomatid water bug. From these serial sections, we achieved entire myofibrillar filament counts at the level of the A band, and at the I-Z junctional area. Based on our results we conclude that thick filament extensions do not exist in vertebrate muscle, but that they are present in invertebrate flight muscle.

Fine structure of the vertebrate Z-disc

The fine structure of Z-discs from frog, chameleon, rabbit, rat and human muscles was studied. Our data lead us to conclude that the basket-weave (woven) lattice represents the fundamental en face pattern of the vertebrate Z-disc, regardless of the manner of fixation, and we suggest that the large and small-“square” lattices are fixation artifacts. We also find that the woven lattice pattern remains essentially unchanged throughout physiological ranges of resting sarcomere length, and is not detectably altered by active contraction. A model of the vertebrate Z-line, based on anatomical and possible functional considerations, is presented. It presumes that a thin filament, as it enters the Z-line, is continuous with three curved strands which unite with other I-filaments of the same sarcomere. The I-filaments and extending strands from the opposite sarcomere are proposed to be similarly arranged, with the main Z-line substance consisting of the two sets of strands from adjacent sarcomeres. The anatomical features of the Z-line and the phenomenon of “Z-line splitting” are explained by the proposed model. In addition, a potential hexagonal structural arrangement of the Z-line is retained so that a consistent geometrical organization persists throughout the entire sarcomere. Thus, the model also presents a means of understanding the recently suggested role of the Z-line in forming new sarcomeres.

Fine structure of the honeybee Z-disc☆

Abstract Z-discs from the dorsal longitudinal indirect flight muscles of the honeybee (Apis mellifera) are perforated with hundreds of triangular-shaped tubes ordered into an hexagonal array. Each tube is surrounded by 80 A thick rims which incorporate six thin filaments, three from each bordering sarcomere. Although the triangular rims of the tubes are oriented identically in any plane perpendicular to the fibril axis, this orientation changes as the tubes cross the Z-line. The tubes rotate approximately 60 ° about an axis parallel to that of the fibril in passing from one I-Z junction to another. On the basis of filament counting in the A (overlap zone) and I bands of stretched myofibrils, it is concluded that the primary filaments are physically continuous with the Z-lines by material which appears to participate both in the formation of Z-rim substance and the surrounding matrix. Finally, evidence is presented to support the view that filament lattices of adjacent sarcomeres are displaced from one another, so that each thick filament faces the trigonal position of three thick filaments on the other side of the Z-disc.

A theory of contraction for striated muscle

Abstract A theory of contraction for striated muscle is proposed which is consistent with sliding filament morphology and which does not require elaborate interacting mechanisms between actin and myosin. The theory states that muscle functions essentially through the interplay of three components: the Z discs, the sarcolemma and the thick and thin filaments. The structural material of the Z discs is held to undergo a configurational change of expansion with activation of muscle, exerting a force or tension perpendicular to the sarcolemmal surface. Because of the intermolecular cohesive forces of the sarcoplasm, the tension directed outward against the sarcolemma results in an inward tension at the ends of the fiber parallel to the long axis with, if permitted, shortening and widening of the fiber. The sarcolemma plays no role in the transmission of active tension to the ends of the muscle, but serves rather as a container for a constant volume of sarcoplasm, and acts as a barrier to the exchange of fluid across the fiber surface. The resting tension and rest length of muscle are considered to be set (a) by a weak bonding between the thick and thin filaments with the bonding being broken during activation, and (b) by the elasticity of the sarcolemma. The theory offers solutions to many currently unresolved problems in muscle physiology.

The effects of chronic alcohol ingestion in mice on contractile properties of cardiac and skeletal muscle: A comparison with normal and dehydrated-malnourished controls

In vitro isometric contractile tension was measured in heart and skeletal muscle in 3 groups of mice: 1. a control group, 2. a group maintained for 27 weeks on 20% alcohol, and 3. a group whose fluid intake was restricted to the extent equaling that which occurred in the alcohol treated animals. Results showed a reduction in cardiac twitch tension in both the alcohol and fluid restricted group, as compared to normal controls. We therefore consider that dehydration per se may play an important role in the etiology of alcoholic cardiomyopathy.

Analog computer simulation of cardiac muscle contraction

Abstract Isometric and isotonic twitch curves for isolated heart muscle preparations are presented by a differential equation which is programed for analog computing. Computer solutions are shown to describe isotonic and isometric contractions. The technique affords a reliable method for obtaining the derivative of these curves as well as for analyzing the curves for changes produced by experimental procedures.

Changes in Z-disc width of vertebrate skeletal muscle following tenotomy.

Results of unilateral Achilles tenotomy on male rats, after 2–6 weeks, showed conclusively that the Z-lines of tenotomized muscles are significantly wider than those of control, nontenotomized muscles.

Influence of acute hypoxia on Z-line width of cardiac muscle.

Abstract Isolated guinea pig papillary muscles were exposed to 30 min of acute hypoxia. The preparations were then fixed for electron microscopy. The width of 435 control and 386 hypoxic Z-lines were measured. No statistical difference occurred between the two groups. We conclude, contrary to a recent report, that 30 min of acute hypoxia does not alter the Z-line width in heart muscle.