The effect of a combined rehabilitation program on the temporomandibular joint in systemic sclerosis evaluated by ultrasound exam.

PURPOSE: Temporomandibular joint (TMJ) involvement is frequent in Systemic Sclerosis (SSc). Dysfunction and X-ray changes of TMJ were described only in few observational studies. Treatment as well has been seldom considered. Aim of the present study was to evaluate the effects on TMJ of two specifically designed physiotherapy protocols. METHODS: The study group included 26 SSc outpatients (22 females and 4 males with mean age ± SD 59.08 ± 10.31 years). Thirteen patients were randomly assigned to a treatment (protocol 1) including home exercises for TMJ and thirteen to a treatment (protocol 2) including home exercises and a combined procedure. The rehabilitation effects on the TMJ were evaluated by ultrasound examination (UE) in static and dynamic phases. UE was performed in all patients before and at the end of the treatment and after a follow up (8 weeks). RESULTS: Both rehabilitation protocols induced a significant improvement (protocol 1: p < 0.01 and protocol 2: p < 0.005) of mouth opening with a long-lasting effect. Protocol 2 was more effective than protocol 1. A significant increase of bilateral condyle-head temporal bone distance was detected by UE at the end of both treatments. It was maintained at follow-up in patients treated with Protocol 2. CONCLUSIONS: The present investigation shows that a rehabilitation program characterized by home exercises with a combined procedure is useful to recover the function of TMJ. The data also show that UE is helpful in the evaluation of TMJ in SSc and in the assessment of the efficacy of the rehabilitation programs.

Detection of radial crossbridge force by lattice spacing changes in intact single muscle fibers.

Time-resolved lattice spacing changes were measured (10-millisecond time resolution) by x-ray diffraction of synchrotron radiation in single intact muscle fibers of the frog Rana temporaria undergoing electrically stimulated tension development during application of stretches and releases. Ramp releases, which decreased fiber length at constant speed, caused a lattice expansion. After the ramp, increasing tension during recovery was accompanied by lattice compression. Ramp stretches caused a compression of the lattice. While the fiber was held at a constant length after the stretch, tension decreased and lattice spacing increased. These observations demonstrate the existence of a previously undetected radial component of the force generated by a cycling crossbridge. At sarcomere lengths of 2.05 to 2.2 micrometers, the radial force compresses the myofilament lattice. Hence, the myofilament lattice does not maintain a constant volume during changes in force.

Submillisecond changes in myosin lattice spacing resulting from rapid length changes.

The speed of the myofilament lattice spacing response to rapid changes in load or length of single, intact muscle fibres of the frog, was investigated during isometric tetani. During ramp releases at close to Vmax and during step length changes (completed within 250 microseconds), lattice spacing was calculated from the equatorial X-ray diffraction pattern (sampled at 250 microseconds time resolution using synchrotron radiation). Ramp releases (total shortening=1.39 %) caused a spacing increase, described with an exponential function (alpha=271 s-1, amplitude=1.15 nm) plus an elastic component having the time course of discharge of axial tension (amplitude 0.28 nm). For a step release (amplitude=0.87%), lattice expansion could be described with an exponential (alpha =1005 s-1, amplitude=0.56 nm) plus an elastic component of 0.25 nm amplitude. Lattice compression was associated with a step stretch (amplitude=0.62 %), and was also quasi-exponential (alpha=367 s-1, amplitude=0.74 nm), with an elastic component of 0.28 nm. The spacing change time course for length steps resembled that of the accompanying quick recovery of axial tension and the associated change in the meridional 14.5 nm reflection intensity, which are both believed to be determined by the kinetics of the molecular power stroke. Therefore, this shows that lattice spacing changes, arising from radial forces exerted by attached crossbridges, are fast enough to occur during the power stroke event.

Crossbridge viscosity in activated frog muscle fibres.

Force responses to fast ramp stretches at various velocities were recorded in single muscle fibres isolated from tibialis anterior muscle of the frog (Rana esculenta) at a sarcomere length between 2.15 and 3.25 microns at 15 degrees C. Stretches were applied at the tetanus plateau and during tetanus rise. Length changes were recorded at the sarcomere level using either a laser diffractometer or a striation follower apparatus. The immediate force response to the stretch is not simply elastic, as is usually assumed, but is composed of the sum of at least two components: (i) elastic (force proportional to the amount of stretch); and (ii) viscous (force proportional to the rate of stretch). The viscous response is associated with a short (about 10 microseconds) relaxation time. The amplitude of the viscous component increases progressively with tension during the tetanus rise and scales down with sarcomere length approximately in the same way as the tetanic tension. These results suggest that the viscosity of activated fibres may arise from crossbridge kinetics.

Mechanical properties of frog muscle fibres at rest and during twitch contraction.

Data reported in the literature suggest that crossbridges in rapid equilibrium between attached and detached states (weakly binding bridges), demonstrated in relaxed skinned fibres at low ionic strength, could be present also in intact fibres under physiological conditions. In addition, it was suggested that the well known leading of stiffness over force during the tension development in stimulated muscle fibres could be due to an increased number of weakly binding bridges induced by the stimulation. The experiments reviewed in this paper were made to investigate these possibilities. Fast ramp length changes were applied to single frog muscle fibres at rest and during the early phases of activation. The corresponding force changes were analysed, searching for the components expected from the presence of weakly binding bridges. The results showed no mechanical indication for the presence of weakly binding bridges in both skinned and intact fibres, either at rest or during activation. It was also found that a portion of the fibre stiffness increase induced by stimulation leads the formation of crossbridges.

Force response of unstimulated intact frog muscle fibres to ramp stretches.

The possibility that weakly binding bridges are attached to actin in the absence of Ca2+ under physiological conditions was investigated by studying the force response of unstimulated intact muscle fibres of the frog to fast ramp stretches. The force response during the stretching period is divided into two phases: phase 1, coincident with the acceleration period of the sarcomere length change and phase 2, synchronous with sarcomere elongation at constant speed. The phase 1 amplitude increases linearly with the stretching speed in all the range tested, while phase 2 increases with the speed but reaches a plateau level at about 50 x 10(3) nm/half sarcomere per second. The analysis of data shows that phase 1, which corresponds to the initial 5-10 nm/half sarcomere of elongation, is very likely a pure viscous response; its amplitude increases with sarcomere length and it is not affected by the electrical stimulation of the fibre. Phase 2 is a viscoelastic response with a relaxation time of the order of 1 ms; its amplitude increases with sarcomere lengths and with the stimulation. These data suggest that weakly binding bridges are not present in a significant amount in unstimulated intact fibres.

The mechanical characteristics of the contractile machinery at different levels of activation in intact single muscle fibres of the frog.

The relation between stiffness and tension and the characteristics of the early tension recovery in response to applied small length step were studied both during tetanus rise and redevelopment of tension following a period of shortening at Vmax. Experiments were performed on single fibres isolated from tibialis anterior and lumbricalis muscles of the frog. Development of stiffness preceded that of tension during tension redevelopment, but the leading of stiffness was reduced to about one half of that found during the tetanus rise. The relation between relative stiffness and relative tension was the same either during tetanus rise and tension redevelopment. The speed of the early tension recovery in response to a step length change applied during the tension redevelopment was unchanged with respect to that found at the same tension during the tetanus rise. These results suggest that a cross-bridge state generating no force (or low force) may be a normal intermediate of the cross-bridge cycle even when the fibre is fully activated.

Myofilament compliance and sarcomere tension-stiffness relation during the tetanus rise in frog muscle fibres.

The sarcomere stiffness was measured in single muscle fibres during the development of tetanic tension using a method insensitive to fibre inertia and viscosity. The stiffness was calculated as the ratio between tension changes and sarcomere length changes during a period of fast sarcomere elongation at constant velocity. The results show that, unlike previous measurements with step or sinusoidal length changes, the relation between relative force and relative stiffness on the tetanus rise is linear. Consequently, the development of stiffness upon stimulation is synchronous with the development of force. Since a substantial fraction of sarcomere compliance is localized in the myofilaments, this result can be accounted for by assuming that either myofilament compliance is highly non-linear or that crossbridges stiffness during the tetanus rise is not proportional to crossbridge tension.

Time-resolved equatorial X-ray diffraction measurements in single intact muscle fibres.

Equatorial X-ray diffraction techniques have been successfully applied to the intact single muscle fibre preparation under length clamp and "fixed end" conditions. 10 and 11 intensity changes and stiffness have been measured in the same preparation. Under isometric conditions, equatorial signals and stiffness led force by 14-20ms during the rise of tetanic tension. During relaxation, stiffness and equatorial signals lagged force. The time course of the intensity changes suggests a low force crossbridge state is present to a greater extent during the rise of tetanic tension and during relaxation than at the tetanus plateau. During isotonic shortening at Vmax, stiffness fell to 30% of its isometric level, while equatorial signals fell to 60%. Since stiffness and equatorial signals are thought to detect attached crossbridges, either the average stiffness per attached bridge measured at 4kHz during shortening is less than at the plateau, or the relation between equatorial intensities and the proportion of attached crossbridges during isotonic shortening differs from that measured under isometric conditions. Active tension also affects the lattice spacing. The myosin lattice was compressed during the development of longitudinal force. This implies a radial component of crossbridge tension. The lattice compression was smaller in a compressed lattice and larger in an expanded lattice.

Studies on the 14.5 nm meridional X-ray diffraction reflection during length changes of intact frog muscle fibres.

The intensity of the 14.5 nm meridional reflection (M3) from activated skeletal muscle fibres was studied in both single fibres and fibre bundles during the imposition of length changes. During shortening at small load, the intensity of the reflection decreased within 2 ms to less than 20% of isometric intensity, then recovered partially during the remainder of the shortening. When shortening was terminated, recovery of intensity was delayed. Small shortening steps (0.5% fibre length) produced a fall in M3 intensity (IM3) delayed by ca. 250 microseconds compared to the fall in tension. For larger step releases (1% fibre length), the fall in IM3 was not delayed. The fall in IM3 could be almost completely reversed by a subsequent restretch applied within 1.5 ms. Beyond 10 ms after the initial release, the restretch caused a further fall in intensity. A rapid step stretch (0.5% fibre length) also caused a fall in IM3 without delay, which was partially reversed by a release applied within 10 ms. A second small release applied 3 ms (or less) after the first caused a second fall in M3 intensity, but without delay and with faster time course. Small amplitude sinusoidal length oscillations (0.15-0.2% sarcomere; 1 kHz) caused a sinusoidal change in M3 intensity, which was 180 degrees out of phase with the force oscillations, and lacked distortion during its release phase.

Effects of the number of actin-bound S1 and axial force on X-ray patterns of intact skeletal muscle.

Effects of the number of actin-bound S1 and of axial tension on x-ray patterns from tetanized, intact skeletal muscle fibers were investigated. The muscle relaxant, BDM, reduced tetanic M3 meridional x-ray reflection intensity (I(M3)), M3 spacing (d(M3)), and the equatorial I(11)/I(10) ratio in a manner consistent with a reduction in the fraction of S1 bound to actin rather than by generation of low-force S1-actin isomers. At complete force suppression, I(M3) was 78% of its relaxed value. BDM distorted dynamic I(M3) responses to sinusoidal length oscillations in a manner consistent with an increased cross-bridge contribution to total sarcomere compliance, rather than a changed S1 lever orientation in BDM. When the number of actin-bound S1 was varied by altering myofilament overlap, tetanic I(M3) at low overlap was similar to that in high [BDM] (79% of relaxed I(M3)). Tetanic d(M3) dependence on active tension in overlap experiments differed from that observed with BDM. At high BDM, tetanic d(M3) approached its relaxed value (14.34 nm), whereas tetanic d(M3) at low overlap was 14.50 nm, close to its value at full overlap (14.56 nm). This difference in tetanic d(M3) behavior was explicable by a nonlinear thick filament compliance which is extended by both active and passive tension.

Myosin lever disposition during length oscillations when power stroke tilting is reduced.

M3 reflection intensity (I(M3)) from tetanized, intact skeletal muscle fiber bundles was measured during sinusoidal length oscillations at 2.8 kHz, a frequency at which the myosin motor's power stroke is greatly reduced. I(M3) signals were approximately sinusoidal, but showed a "double peak" distortion previously observed only at lower oscillation frequencies. A tilting lever arm model simulated this distortion, where I(M3) was calculated from the molecular structure of myosin subfragment 1 (S1). Simulations showed an isometric lever arm disposition close to normal to the filament axis at isometric tension, similar to that found using lower oscillation frequencies, where the power stroke contributes more toward total S1 movement. Inclusion of a second detached S1 in each actin-bound myosin dimer increased simulated I(M3) signal amplitude and improved agreement with the experimental data. The best agreement was obtained when detached heads have a fixed orientation, insensitive to length changes, and similar to that of attached heads at tetanus plateau. This configuration also accounts for the variations in relative intensity of the two main peaks of the M3 reflection substructure after a length change. This evidence of an I(M3) signal distortion when power stroke tilting is suppressed, provided that a large enough amplitude of length oscillation is used, is consistent with the tilting lever arm model of the power stroke.

Crossbridge kinetics in single frog muscle fibres in presence of ethylene glycol.

Single fibres isolated from frog muscle were tetanically stimulated at 14 degrees C to produce isometric tetani at a sarcomere length of about 2.16 microm, using a striation follower device to measure the sarcomere length of a selected segment of fibre. Force-velocity data were obtained by applying ramp releases at pre-set velocity at the tetanus plateau. Sarcomere stiffness was measured at isometric plateau and during isotonic shortening by using sinusoidal length changes at 2 kHz frequency and about 1 nm per half sarcomere (hs) peak to peak amplitude. A correction method was used to compensate for the force truncation due to the quick recovery. After data collection, the bathing solution was substituted with Ringer plus ethylene glycol (EG) at 2 M (11.2% v/v). When the fibre was fully equilibrated with the new solution, the measurements were repeated. Ethylene glycol reduced the speed of the tetanus rise and tetanus relaxation without altering the isometric tension, and reduced the maximum shortening velocity by about 20%. During isotonic contraction tension and stiffness at each given shortening velocity were reduced by about the same amount, so that the stiffness/tension ratio remained almost unaltered. Force-velocity and stiffness data in both standard and EG Ringer were analysed in terms of a two state model (Huxley, 1957). The analysis showed that our results can be accounted for by assuming that EG at 2 M concentration reduces all the rate constants for crossbridges interaction by about the same amount.

Absence of mechanical evidence for attached weakly binding cross-bridges in frog relaxed muscle fibres.

1. Passive force responses to ramp stretches at various velocities were measured in intact and skinned single muscle fibres isolated from the lumbricalis muscle of the frog. Force was measured using a fast capacitance transducer and sarcomere length was measured using a laser light diffraction technique at a point very close to the fixed end so as to avoid effects of fibre inertia. Experiments were performed at 15 degrees C with sarcomere length between 2.13 and 3.27 microns under high (170 mM) and low (20 mM) ionic strength. 2. The analysis shows that the force response is the sum of at least three components: (i) elastic (force proportional to the amount of stretch), (ii) viscous (force proportional to rate of stretch), and (iii) viscoelastic (resembling the response of a pure viscous element in series with an elastic element). 3. The amplitude of all these components increased progressively with sarcomere length in the whole range measured. 4. A further component, attributable to the short-range elasticity (SREC), was present in the force response of the intact fibres. 5. The amplitude of the force response decreased substantially upon skinning at high ionic strength but increased again at low ionic strength. The SREC was completely abolished by skinning. 6. None of the components of the force response was found to have the properties expected from the previously postulated 'weakly binding bridges'.

Development of stiffness precedes cross-bridge attachment during the early tension rise in single frog muscle fibres.

1. Force responses to ramp stretches were recorded in single muscle fibres isolated from the lumbricalis muscle of the frog. Stretches were applied at rest and at progressively increasing times after a single stimulus. 2. The increase of fibre stiffness that precedes tension development has a 'static' component that accounts for the whole fibre stiffness increase during the latent period and at very low tension at the beginning of the twitch. 3. Static stiffness increase was not affected by 2,3-butanedione-2-monoxime, a drug that almost completely inhibited twitch tension. 4. Static stiffness increased approximately 5-fold as the sarcomere length was increased from 2.1 to 2.84 microns. 5. These results suggest that static fibre stiffness increase is not attributable to the formation of non-force-generating cross-bridges.

Plateau and descending limb of the sarcomere length-tension relation in short length-clamped segments of frog muscle fibres.

1. The relation between sarcomere length and tetanic tension was determined at 10-12 degrees C for 70-80 microns long segments of single fibres isolated from the tibialis anterior and semitendinosus muscles of the frog. Measurements of segment striation spacings were performed during fixed-end or length-clamp contractions by means of a laser light diffractometer. 2. At sarcomere lengths of around 2.10 microns tetanic tension rose promptly to a steady plateau, independent of the recording conditions. At greater sarcomere lengths under fixed-end conditions the tension rise occurred in two distinct stages: an initial rapid rise followed by a much slower creep. The tension creep was entirely abolished in length-clamp contractions. 3. The sarcomere length-tension diagram of length-clamped segments of tibialis anterior fibres exhibited a definite flat region between about 1.96 and 2.16 microns where tension varied by less than 1.5%. The highly linear descending limb reached zero tension at about 3.53 microns. The shift to the left by about 0.10 microns, with respect to the length-tension diagram of length-clamped segments of semitendinosus fibres, may be tentatively explained by assuming that thin filament lengths vary in different muscles. 4. The results are in agreement with those of a previous work by Gordon, Huxley & Julian (1966) and support the hypothesis (Huxley, 1957, 1980) that muscle tension is produced by simultaneous action of independent force generators, in proportion to the number of myosin bridges overlapped by actin filaments.

A model of force production that explains the lag between crossbridge attachment and force after electrical stimulation of striated muscle fibers.

Whereas the mechanical behavior of fully activated fibers can be explained by assuming that attached force-producing crossbridges exist in at least two configurations, one exerting more force than the other (Huxley A. F., and R. M. Simmons. 1971. Nature [Lond.]. 233:533-538), and the behavior of relaxed fibers can be explained by assuming a single population of weakly binding rapid-equilibrium crossbridges (Schoenberg, M. 1988. Biophys. J. 54:135-148), it has not been possible to explain the transition between rest and activation in these terms. The difficulty in explaining why, after electrical stimulation of resting intact frog skeletal muscle fibers at 1-5 degrees C, force development lags stiffness development by more than 15 ms has led a number of investigators to postulate additional crossbridge states. However, postulation of an additional crossbridge state will not explain the following three observations: (a) Although the lag between force and stiffness is very different after stimulation, during the redevelopment of force after an extended period of high velocity shortening, and during relaxation of a tetanus, nonetheless, the plots of force versus stiffness in each of these cases are approximately the same. (b) When the lag between stiffness and force during the rising phase of a twitch is changed nearly fourfold by changing temperature, again the plot of force versus stiffness remains essentially unchanged. (c) When a muscle fiber is subjected to a small quick length change, the rate constant for the isometric force recovery is faster when the length change is applied during the rising phase of a tenanus than when it is applied on the plateau. We have been able to explain all the above findings using a model for force production that is similar to the 1971 model of Huxley and Simmons, but which makes the additional assumption that the force-producing transition envisioned by them is a cooperative one, with the back rate constant of the force-producing transition decreasing as more crossbridges attach.

Effects of 2,3-butanedione monoxime on the crossbridge kinetics in frog single muscle fibres.

The effects of 2,3-butanedione monoxime (BDM) on contraction characteristics were studied at 5 degrees C in single intact fibres isolated from the tibialis anterior muscle of the frog. The force-velocity relation was determined using the controlled-velocity method in either whole fibres or short fibre segments in which sarcomere shortening was measured by a laser light diffraction method. It is shown that 3 mM BDM decreases the speed of rise and the amount of tetanus tension, reduces the maximum velocity of shortening and increases the curvature of the force-velocity relation, as well as the value for the stiffness to tension ratio. BDM also slowed down the redevelopment of tetanus tension after a period of unloaded shortening both in fixed-end and in length-clamp conditions. In normal and in BDM-treated fibres length-clamping increased the speed of the initial rise of tetanus tension but not that of the recovery after shortening. The observed force-velocity data points were fitted by the Huxley (1957) equation. It was found that BDM produces a conspicuous decrease of the rate constant for crossbridge attachment. This effect, and also a reduction of the force per crossbridge, are responsible for the depression of the contractile characteristics produced by BDM.

Are weakly binding bridges present in resting intact muscle fibers?

Several experimental results (Schoenberg, M. 1988. Biophys. J. 54:135-148) have shown that the force response of relaxed skinned muscle fibers to fast stretches arises from the presence of cross-bridges rapidly cycling between attached and detached states. These bridges were identified with the M.ATP<-->AM.ATP and M.ADP.Pi<-->AM.ADP.Pi states seen in solution and are commonly referred to as weakly binding bridges. In this paper we have investigated the possibility that weakly binding bridges are also present in resting intact muscle fibers. The force response to fast stretches can be accounted for by assuming the presence in the fiber of a viscous and a viscoelastic passive component arranged in parallel. None of these components has the properties previously attributed to weakly binding bridges. This shows that in intact resting fibers there is no mechanical evidence of attached cross-bridges, suggesting that, under physiological conditions, either the M.ATP or M.ADP.Pi states have a negligibly small affinity for actin or the AM.ATP and AM.ADP.Pi cross-bridge states are unable to bear tension and contribute to fiber stiffness.

Sarcomere tension-stiffness relation during the tetanus rise in single frog muscle fibres.

The sarcomere stiffness was measured in single muscle fibres during the development of tetanic tension using a method insensitive to fibre inertia and viscosity. The stiffness was calculated by measuring the ratio between tension and sarcomere length during a period of fast sarcomere elongation at constant velocity. Tension changes were corrected for force truncation by the quick recovery mechanism. The results show that the relation between force and stiffness deviates from the direct proportionality less than previously reported. If the deviation is due to the presence of a linear myofilament compliance in series with the cross-bridges, our data suggest that myofilament compliance accounts for about 30% of the sarcomere compliance. This value is significantly smaller than 50-70% determined by X-ray diffraction measurements. These two different findings, however, may be reconciled by assuming that the myofilament compliance is non-linear increasing appropriately at low tension.