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R A Meiss

Publications and source records attributed to R A Meiss.

32 records · Page 2Linked to original sources
PubMed1987

Stiffness of active smooth muscle during forced elongation.

The stiffness of isometrically contracting mesotubarium superius and ovarian ligament smooth muscle from estrous female rabbits was measured continuously by using sinusoidal length perturbations (at 80 Hz, less than 15 microns peak to peak). Muscles were stimulated with alternating current fields, and all records were digitized using a microcomputer system. Phase-angle data were used to resolve computed stiffness into elastic and viscous components. Stiffness measurements were continued during long ramp-type stretches (up to 25% of muscle length) delivered as soon as force was maximal. To use the period of isometric tension development as a standard for comparison, the expected stiffness was computed during the long stretch. Stiffness was reduced in approximate proportion to the ramp stretch rate, and the reduction was confined largely to the elastic component. Cooling the muscle increased the stiffness deviation at a given stretch rate. It is proposed that the long stretch detaches cross bridges that can reattach to new sites as myofilaments shear past one another. At higher shearing speeds, less time is available for reattachment and stiffness is further reduced.

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PubMed1984

Nonlinear force response of active smooth muscle subjected to small stretches.

Isometrically mounted and electrically stimulated strips of rabbit mesotubarium superius muscles were subjected to sinusoidal length perturbations (delta L) of variable amplitude (0-1% of Lmax) at constant frequency (80 Hz). In both the plateau phase of long-maintained (steady-state) contractions and in brief contraction-relaxation cycles the force perturbation amplitude (delta F) response was directly proportional to delta L (and to the developed force, F) for delta L values less than approximately 0.30% of Lmax. At larger delta L values the magnitude of the delta F response deviated downward from a linear relationship. Statistical analysis of the relationship characterized a "deviation point," the value of delta F and delta L beyond which the delta F response departed from linearity. The value of delta F at the deviation point depended strongly on the developed force, whether it was varied by changing muscle rest length, stimulus strength, or time during a phasic contraction-relaxation cycle. The value of delta L at the deviation point was independent of developed force. Restricting the length of muscle subjected to delta L (while not changing cellular dimensions) showed that the slope of delta F/delta L relationship (the active stiffness) depended inversely on the length of muscle in the system. These findings are consistent with a model in which the active elasticity arises from cross bridges that are borne on myofilaments and that both generate and transmit the muscle force.

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PubMed1984

Solid-state optical scanning system for remote measurements in biomechanical systems.

A remote optical sensing system, employing a self-scanning photodiode array, is described, and its operation is demonstrated for measurements of rapid dimensional changes in contracting smooth muscle preparations. The single-line sensor array, a commercially available charge-coupled device integrated circuit, with 256 elements at 25-microns intervals, is mounted in the image plane of an optical system focused on a backlit test object. The amplitude profile of each scan is proportional to the illumination reaching the individual sensory elements. Auxilliary circuitry generates a raster of successive scan lines on the face of a storage oscilloscope. Spatial and temporal information about the target and its motions may be derived from the displayed raster scan. Performance is illustrated using an artificial target and a muscle fiber bearing opaque markers. Successive lines may be scanned in as briefly as 5 ms (at 10-ms intervals) or in as long as 50 ms (at 1-s intervals). Each raster may contain up to 256 lines, although not all of the lines need to be displayed. The spatial resolution is determined by the photodiode spacing in the sensory array and by the magnitude of the optical system in use; as described here, the resolution is on the order of 0.2 mm for a 20-mm scan length.

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PubMed1984

Human mononuclear cell factors suppress contractility of isolated mouse soleus muscle.

Weakness in polymyositis-dermatomyositis is often greater than would be suggested by histologic evidence of fiber degeneration or necrosis. Mononuclear cell infiltration is the key pathologic feature of polymyositis-dermatomyositis, and previous studies suggest a role for cellular immunity. In this study, the effect of supernatants from mitogen-stimulated human blood mononuclear cells on contractility of isolated mouse normal soleus muscle was examined. Mononuclear cell factor-rich supernatants were generated in 5-day cultures by phytohemagglutinin P stimulation of mononuclear cells from normal volunteers. Mouse soleus muscle was mounted isometrically in a muscle bath filled with oxygenated Ringer's solution or RPMI-1640 and was stimulated electrically. In 10 individual experiments, all muscles exposed to mononuclear cell factor-rich supernatants showed a rapid and progressive decline in active force of isometric contraction; a 40% decrease in active force was observed 5 to 13 minutes (average, 8 minutes) after the addition of supernatant. The inhibitory effect was reversible on removal of mononuclear cell factor-rich supernatants. Control culture medium and supernatants from unstimulated cell cultures showed no appreciable effect on active force. The factor(s) producing suppression of muscle contractility was dialyzable and stable through several cycles of freezing and thawing. Gel chromatography (Sephadex G-25 fine) showed one active fraction corresponding to an apparent molecular weight of approximately 2000. These data indicate that factor(s) released by human mononuclear cells can directly suppress the contraction of normal skeletal muscle.

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PubMed1982

Transient responses and continuous behavior of active smooth muscle during controlled stretches.

Controlled length changes were imposed on mesotubarium superius and ovarian ligament smooth muscles from the reproductive tracts of female rabbits in constant estrus. Stretches of up to 35% of the muscle length were applied during isometric contraction, relaxation, and steady-state force levels. Force was continuously monitored and was plotted as a function of length. During constant velocity stretches there was an initial steep rise in force, a rapid downward deviation from the initial slope, and a long region with a constant upward slope. Stretches made during contraction showed smaller initial rises in force and steeper linear portions than did identical comparison stretches made during relaxation. The value of the slope was independent of the prior developed force, but it did depend on whether the muscle was contracting or relaxing. During contraction and steady-state force levels, the slope was independent of the stretch rate, but it was strongly rate dependent during relaxation. Changes in the stretch rate during stretch caused associated changes in muscle force; the relationship was curvilinear and was exaggerated during relaxation. The findings are placed in the context of a sliding-filament--cross-bridge hypothesis.

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PubMed1978

Dynamic stiffness of rabbit mesotubarium smooth muscle: effect of isometric length.

The dynamic stiffness of mesotubarium smooth muscle from nonpregnant adult rabbits was measured continuously during isometric contraction by applying small (0.5 percent of the muscle length) sinusoidal length perturbations and measuring the amplitude and phase of the resulting tension perturbations. Stiffness during contraction was directly proportional to muscle tension; during relaxation stiffness at all tensions was significantly increased as compared to the values encountered during the rise of tension. Peak isometric tension and dynamic stiffness (determined at a common tension level) both decreased at shorter muscle lengths; the relative falloff in stiffness was significantly less than the tension decrease. Varying levels of muscle activation (obtained by changing stimulus strength and by applying quick releases to active muscle) had little effect on the measured elastic modulus. Comparisons of these results with published data on single-cell contractile properties imply a cellular locus for a portion of the measured stiffness.

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PubMed1975

Graded activation in rabbit mesotubarium smooth muscle.

The outer margin of the mesotubarium superius, an accessory ligament from the femal rabbit reproductive system, contains a long and slender bundle of smooth muscle fibers well aligned with the long axis of the tissue. Very little connective tissue is present. Massive alternating-current electrical field stimuli (variable in frequency, amplitude, and duration) applied to isolated mesotubaria from mature, nonpregnant animals produced contractions in which isometric force (P) and its first derivative (dP/dt) could be continuously graded; an optimum existed for stimulus frequency and amplitude, but not for its duration. Twitchlike contractions could not be produced. Isometric contractions in which P was plotted against dP/dt to generate a phase-plane trajectory were used to predict the ultimate (time = infinity) force (Po) in graded contractions; this value agreed with the Po derived from isotonic force-velocity curves fitted to the Hill equation. Quick stretches applied during the rise of contractile force revealed a slow onset of the ability to bear the Po force.

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