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PubMed1973

Energetics of shortening muscles in twitches and tetanic contractions. II. Force-determined shortening heat.

The extra heat liberation accompanying muscular shortening, the force-determined shortening heat, is defined as the difference between the heat produced when shortening occurs and that produced in an isometric contraction developing the same amount of force and performing the same amount of internal work. Based on this definition, the initial energy production in twitches and tetanic contractions (E) is given by E = A + f (P, t) + alpha(F)x + W, where A is the activation heat, f(P, t), the tension-related heat (a heat production associated with the development and maintenance of tension), alpha(F)x, the force-determined shortening heat, and W, the external work. It is demonstrated that this equation accurately accounts for the time-course of heat evolution and the total initial energy production in both twitches and tetani at 0 degrees C. The force-determined shortening heat is liberated, during shortening, in direct proportion to (a) the distance shortened, and (b) the force against which shortening occurs. The normalized value of the force-determined shortening heat coefficient, alpha(F)/P(o), is the same in both the twitch and the tetanus. Finally, this formulation of the muscle's energy production also accounts for the total energy production in afterload isotonic twitches at 20 degrees C, where a Fenn effect is not demonstrable.

Animals↗
PubMed1999

Contractile properties of muscles used in sound production and locomotion in two species of gray tree frog.

The sound-producing muscles of frogs and toads are interesting because they have been selected to produce high-power outputs at high frequencies. The two North American species of gray tree frog, Hyla chrysoscelis and Hyla versicolor, are a diploid-tetraploid species pair. They are morphologically identical, but differ in the structure of their advertisement calls. H. chrysoscelis produces very loud pulsed calls by contracting its calling muscles at approximately 40 Hz at 20 degrees C, whereas, H. versicolor operates the homologous muscles at approximately 20 Hz at this temperature. This study examined the matching of the intrinsic contractile properties of the calling muscles to their frequency of use. I measured the isotonic and isometric contractile properties of two calling muscles, the laryngeal dilator, which presumably has a role in modulating call structure, and the external oblique, which is one of the muscles that provides the mechanical power for calling. I also examined the properties of the sartorius as a representative locomotor muscle. The calling muscles differ greatly in twitch kinetics between the two species. The calling muscles of H. chrysoscelis reach peak tension in a twitch after approximately 15 ms, compared with 25 ms for the same muscles in H. versicolor. The muscles also differ significantly in isotonic properties in the direction predicted from their calling frequencies. However, the maximum shortening velocities of the calling muscles of H. versicolor are only slightly lower than those of the comparable muscles of H. chrysoscelis. The calling muscles have similar maximum shortening velocities to the sartorius, but have much flatter force-velocity curves, which may be an adaptation to their role in cyclical power output. I conclude that twitch properties have been modified more by selection than have intrinsic shortening velocities. This difference corresponds to the differing roles of shortening velocity and twitch kinetics in determining power output at differing frequencies.

Animals↗
PubMed1974

Membrane currents and activation of contraction in rat ventricular fibres.

1. A double sucrose gap technique has been combined with an optical method of measuring the movement of the preparation and applied to rat ventricular trabeculae.2. Experiments performed in normal McEwen and in depleted sodium solutions with and without tetrodotoxin, manganese or predepolarization suggest that the fast inward current is not as important as the slow inward current in determining the contractile strength. Furthermore, there is a marked similarity between potential dependence of the slow inward current and the contraction, particularly in sodium-depleted fluids.3. The appearance of a staircase response associated with a series of depolarizations, in normal McEwen, may mean that there is an intervention of a further, possibly intracellular, stage between inward current and contraction, as suggested by earlier experiments on frog as well as on mammalian heart.

Animals↗
PubMed1976

Increase in resting tension of tracheal muscle due to rigor during metabolic inhibition.

Resting tension of canine tracheal smooth muscle increased when glucose and oxygen were withdrawn from the bathing medium. Similar treatment of muscle stimulated with carbachol caused first a relaxation and then a secondary increase in tension. The increase in tension due t0 metabolic inhibition, unlike normal tracheal contractions, was insensitive to calcium depletion, was not associated with an active state, and was accompanied by marked reduction of tissue adenosine triphosphate, creatine phosphate, and glycogen content. Because muscle stiffness was also increased we concluded that hypoxic glucose-free contracture is due to rigor and not to an increased tissue calcium level as has been previously suggested. Rigor shortening during lightly loaded isotonic conditions is better maintained than rigor tension during isometric conditions. Our results also indicate that rigor tension is reduced irreversibly on imposition of a load and, therefore, the load-extension relationship during rigor in smooth muscle should be studied by making only small load changes.

Adenosine Triphosphate↗
PubMed1999

Vanadate and the absence of myofibroblasts in wound contraction.

HYPOTHESIS: Fibroblasts, not myofibroblasts, are responsible for wound contraction. Only myofibroblasts express a smooth muscle actin for which vanadate blocks its expression. Wound contraction in vanadate-treated rats will proceed normally in the absence of myofibroblasts. DESIGN: Laboratory study using rats. METHODS: Wound healing in rats receiving vanadate parenterally, an inhibitor of tyrosine phosphate phosphatases, was investigated. For 21 days, treated rats received drinking water containing vanadate, 0.2 mg/mL, in isotonic sodium chloride solution, and the control rats received isotonic sodium chloride solution alone. On day 7, 4 square, full-excision wounds were made dorsally and measured, then 2 polyvinyl alcohol sponges were placed ventrally in subcutaneous pockets. RESULTS: After 2 weeks, the wound area in the rats receiving vanadate measured 7.1 +/- 1.8 U (mean+/-SD), and the wound area in the control rats measured 7.2 +/- 2.2 U. The control rats' granulation tissue (GT) had myofibroblasts, or alpha-smooth muscle (alpha-SM) actin-positive fibroblasts, whereas the vanadate-treated group's fibroblasts were devoid of alpha-SM actin. By Western blot analysis, GT homogenates in the vanadate-treated group contained less alpha-SM actin. By electron microscopy, control rats' GT showed classic myofibroblast populations, and the collagen fiber bundles were randomly organized. In contrast, the wounds in the vanadate-treated group showed unencumbered fibroblast populations and neatly ordered, parallel collagen fiber bundles. By polarized light microscopy, the GT of the vanadate-treated group displayed orderly collagen fiber bundles. CONCLUSIONS: The differentiation of fibroblasts into myofibroblasts requires the dephosphorylation of selected tyrosine phosphate residues. In the absence of myofibroblasts, the rate of rat wound contraction is normal, and collagen fiber bundles have a more orderly arrangement. Myofibroblasts are not required for wound contraction.

Animals↗
PubMed2002

Appearance of peristaltic reflex in isolated guinea pig ileum in response to boluses of air, water, oil, and cellulose.

Distension of an isolated preparation of guinea pig ileum triggers the peristaltic reflex, a characteristic movement of the intestinal walls which generates luminal pressures and clearance of luminal contents. To determine how the reflex responds to properties of luminal contents, we compared the responses triggered by boluses of air, oil, and cellulose to boluses of Krebs' solution. We found that oil and cellulose increased pressures and contraction length and decreased outflow. Cellulose, but not oil, slowed the velocity with which the contraction propagated and increased the delay with which the end point (upstream edge) of the contraction started to propagate after the lead point (downstream edge). Air tended to produce short contraction segments and high velocity. We conclude that bolus properties such as viscosity determine the response that isolated intestinal segments generate to distension. Response patterns are reflected in contraction length, propagation velocity, and other visual parameters that define wall movements.

Air↗
PubMed2004

Oxytocin stimulates colonic motor activity in healthy women.

The effects of oxytocin in the gastrointestinal tract are unclear. The aim of this study was to examine the effect of infusion of oxytocin on colonic motility and sensitivity in healthy women. Fourteen healthy women were investigated twice. A 6-channel perfusion catheter, with three recording points (2 cm apart) proximally and three recording points distally to a barostat balloon, was inserted to the splenic flexure. An intestinal feeding tube was placed in the mid-duodenum. A 90-min duodenal lipid infusion of 3 kcal min(-1) was administered. Thirty minutes after the start of the lipid infusion, the subject randomly received either 20 or 40 mU min(-1) of oxytocin, or isotonic saline as intravenous infusions for 90 min. Meanwhile, the colonic motility was recorded. During the last 30 min of oxytocin and saline infusion, the visceral sensitivity to balloon distensions was examined. During lipid infusion the number of antegrade contractions per hour was 0.7 +/- 0.3 after saline and 3.9 +/- 1.4 after oxytocin (P = 0.03), indicating more pronounced lumen-occlusive contractile activity after oxytocin administration. Some of these consisted of high-amplitude (> 103 mmHg in amplitude) antegrade contractions. Lipid infusion evoked a decrease of the balloon volume, reflecting increased colonic tone, but there was no difference between saline and oxytocin. Sensory thresholds did not differ significantly between saline and oxytocin. Infusion of oxytocin stimulates antegrade peristaltic contractions in stimulated colon in healthy women. The effects of oxytocin on colonic motor activity deserve to be further explored, especially in patients with colonic peristaltic dysfunction.

Adult↗
PubMed1988

Regulation of shortening velocity by cross-bridge phosphorylation in smooth muscle.

We have proposed a model that incorporates a dephosphorylated "latch bridge" to explain the mechanics and energetics of smooth muscle. Cross-bridge phosphorylation is proposed as a prerequisite for cross-bridge attachment and rapid cycling. Features of the model are 1) myosin light chain kinase and phosphatase can act on both free and attached cross bridges, 2) dephosphorylation of an attached phosphorylated cross bridge produces a noncycling "latch bridge," and 3) latch bridges have a slow detachment rate. This model quantitatively predicts the latch state: stress maintenance with reduced phosphorylation, cross-bridge cycling rates, and ATP consumption. In this study, we adapted A. F. Huxley's formulation of crossbridge cycling (A. F. Huxley, Progr. Biophys. Mol. Biol. 7: 255-318, 1957) to the latch-bridge model to predict the relationship between isotonic shortening velocity and phosphorylation. The model successfully predicted the linear dependence of maximum shortening velocity at zero external load (V0) on phosphorylation, as well as the family of stress-velocity curves determined at different times during a contraction when phosphorylation values varied. The model implies that it is unnecessary to invoke an internal load or multiple regulatory mechanisms to explain regulation of V0 in smooth muscle.

Algorithms↗
PubMed1998

Functional and molecular identification of a novel chloride conductance in canine colonic smooth muscle.

Swelling-activated or volume-sensitive Cl- currents are found in numerous cell types and play a variety of roles in their function; however, molecular characterization of the channels is generally lacking. Recently, the molecular entity responsible for swelling-activated Cl- current in cardiac myocytes has been identified as ClC-3. The goal of our study was to determine whether such a channel exists in smooth muscle cells of the canine colon using both molecular biological and electrophysiological techniques and, if present, to characterize its functional and molecular properties. We hypothesized that ClC-3 is present in colonic smooth muscle and is regulated in a manner similar to the molecular entity cloned from heart. Indeed, the ClC-3 gene was expressed in colonic myocytes, as demonstrated by reverse transcriptase polymerase chain reaction performed on isolated cells. The current activated by decreasing extracellular osmolarity from 300 to 250 mosM was outwardly rectifying and dependent on the Cl- gradient. Current magnitude increased and reversed at more negative potentials when Cl- was replaced by I- or Br-. Tamoxifen ([Z]-1-[p-dimethylaminoethoxy-phenyl]-1,2-diphenyl-1-butene; 10 microM) and DIDS (100 microM) inhibited the current, whereas 25 microM niflumic acid, 10 microM nicardipine, and Ca2+ removal had no effect. Current was inhibited by 1 mM extracellular ATP in a voltage-dependent manner. Cl- current was also regulated by protein kinase C, as phorbol 12,13-dibutyrate (300 nM) decreased Cl- current magnitude, while chelerythrine chloride (30 microM) activated it under isotonic conditions. Our findings indicate that a current activated by hypotonic solution is present in colonic myocytes and is likely mediated by ClC-3. Furthermore, we suggest that the ClC-3 may be an important mechanism controlling depolarization and contraction of colonic smooth muscle under conditions that impose physical stress on the cells.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1976

Dependence of the heat production of active muscle on the length of muscle.

The dependence of the heat production of muscle on length was examined in isometric (with stretch) and isotonic (free of stretch) tetanuses of 2 s. The isometric heat production was significantly greater than the isotonic one at any length of muscle. The isometric heat coefficient (Flo/Q, where F is the active tension development of muscle measured in ponds, lo is the resting length measured in cm, Q is the heat production during the contraction at a given length measured in mcal) was not constant but dependent on the length of muscle, and had an extreme value near the resting length (lo). A close positive correlation was found between the active tension development and the heat production of the muscle.

Animals↗
PubMed1985

Guidelines for rehabilitation of sports injuries.

Rehabilitation involves a functional progression through a systematic program of physical reconditioning involving the re-establishment of intact articulations and muscles, pain-free joints and muscles, joint flexibility, muscular strength, muscular endurance, muscular speed, integrated and coordinated movement (skill patterns), and cardiovascular endurance. Specific demands must be imposed upon the body to bring about redevelopment of each phase. A proper diagnosis prior to beginning, and constant monitoring of the patient's progress during, rehabilitation are necessary so that the demands of the therapeutic regimen can be adjusted according to the patient's progress. The DAPRE technique objectifies isotonic and loaded isometric strength development and therefore stimulates greater strength gains during rehabilitation than other techniques do.

Athletic Injuries↗
PubMed1985

Histochemical and physiological characteristics of the rat diaphragm.

The histochemical and contractile characteristics of the adult rat diaphragm were determined. Based on enzyme histochemistry, the rat diaphragm contained 40% type I, 27% type IIa, and 34% type IIb fibers. There were significantly more type I fibers in the ventral costal (VEN) compared with the crural (CRU) region of the muscle and a slightly higher percentage of type I's on the thoracic relative to the abdominal surface. The contractile properties and the effect of temperature (Q10) were similar in the VEN and CRU regions. Increasing temperature produced higher isometric peak tetanic tension, whereas twitch tension, contraction, and one-half relaxation time all decreased. The maximal shortening velocity increased linearly from 22 and 30 degrees C, then plateaued before decreasing between 35 and 37 degrees C. The VEN and CRU force-velocity curves became less concave as temperature increased from 22 to 35 degrees C. Furthermore, the force-frequency relation of both regions was shifted to the right as temperature increased. The isometric and isotonic contractile properties and fiber type distribution are similar in the VEN and CRU regions of the diaphragm. The rat diaphragm is clearly heterogeneous in fiber type distribution and functionally lies intermediate between slow- and fast-twitch limb skeletal muscles.

Animals↗
PubMed1978

[Effects of hypertonic solutions on the excitation-contraction coupling of the skeletal muscle fibre of the crab. II. Ultrastructural aspects (author's transl)].

Experiments were performed to investigate the modifications of electrical activity and the loss of contraction by examination of the ultrastructure. These alterations were obtained with a control physiological solution (artificial sea water, ASW) which was made hypertonic by adding sucrose, glycerol, choline chloride or urea. 1. Under these conditions, the ultrastructural results show that: a) all those substances induce a modification of the coupling junction (either diad or triad). This modification can explain the inhibition of the mechanical phenomenon; b) sucrose (Figs. 6C and 6D) and glycerol (Figs. 4A and 4B) induce alterations of the surface membrane and of the tubular system (less important with glycerol). They can explain the decrease of the resting potential and the abolishment or the modification of the action potential; c) in contrast, choline chloride (Figs. 7A to 7E) and urea (Figs. 9A to 9F) only modify the organisation of the coupling junction. The action potential is maintained. 2. A short exposure of the fibre in an isotonic sucrose solution (Figs. 5A to 5D) deeply modifies the tubular system, particularly, in cutting it off from the sarcolemma. 3. Choline chloride and urea produce similar changes in the ultrastructure but as urea is not ionized, it can be added to the ASW to investigate the electrical phenomenon which cannot be modified by contraction.

Animals↗
PubMed2001

Numerical analysis of Ca2+ depletion in the transverse tubular system of mammalian muscle.

Calcium currents were recorded in contracting and actively shortening mammalian muscle fibers. In order to characterize the influence of extracellular calcium concentration changes in the small unstirred lumina of the transverse tubular system (TTS) on the time course of the slow L-type calcium current (I(Ca)), we have combined experimental measurements of I(Ca) with quantitative numerical simulations of Ca2+ depletion. I(Ca) was recorded both in calcium-buffered and unbuffered external solutions using the two-microelectrode voltage clamp technique (2-MVC) on short murine toe muscle fibers. A simulation program based on a distributed TTS model was used to calculate the effect of ion depletion in the TTS. The experimental data obtained in a solution where ion depletion is suppressed by a high amount of a calcium buffering agent were used as input data for the simulation. The simulation output was then compared with experimental data from the same fiber obtained in unbuffered solution. Taking this approach, we could quantitatively show that the calculated Ca2+ depletion in the transverse tubular system of contracting mammalian muscle fibers significantly affects the time-dependent decline of Ca2+ currents. From our findings, we conclude that ion depletion in the tubular system may be one of the major effects for the I(Ca) decline measured in isotonic physiological solution under voltage clamp conditions.

Animals↗
PubMed2003

Age comparison of H-reflex modulation with the Jendrássik maneuver and postural complexity.

OBJECTIVE: The purpose of this study was to examine modulation of the soleus Hoffmann (H)-reflex in response to the Jendrássik maneuver (JM) in standing positions in young and elderly subjects. METHODS: Seventeen elderly (mean age=72.0 years) and 23 young (mean age=23.2 years) apparently healthy subjects were examined in two separate experiments. The first experiment was conducted to compare the prone and standing position. The second experiment was conducted in the standing position with isotonic glideboard back support. The isotonic glideboard back support was inclined 30 degrees. In the standing position with back support, the knee and ankle joints were set at 0 degrees of flexion. All subjects were tested with two foot-positions: (1) with no soleus contraction on the platform (simple task) and (2) with an active calf muscle group contraction (complex task). To compare the amplitude of the H-reflex in each experiment between the control trials (relaxed) and JM trials (squeezing tennis balls), the stimulus intensity of 1.1 x motor threshold of the M-response was used for each subject in all body positions. RESULTS: To ensure experimental control, subjects did not show a difference in the amplitude of the trial M-response between the control and JM trials on any of the body positions. Also, no difference was found in the mean amplitude of the M-response between two different positions in either of the two experiments. Trial M-responses were all between 13 and 17% of M-max in the quiet standing position for the young subjects, and 17 and 21% for the elderly subjects. Results demonstrated that the JM facilitated the H-reflex in both young and elderly subjects. However, differential ability to modulate motoneuron excitability evoked by H-reflex pathways was found between the two groups. Young subjects demonstrated a significant difference in the amplitude of the H-reflex between control and JM trials in each standing position (P<0.05). The elderly subjects, in contrast, demonstrated no significant difference in the amplitude of the H-reflex between control and JM trials during normal standing. When examining standing with back support, the young subjects demonstrated a significant difference in the amplitude of the H-reflex between control and JM trials during both the simple and complex tasks (P<0.05). The elderly subjects, in contrast, demonstrated a significant difference only in the simple postural task (P<0.05). CONCLUSIONS: These results provide evidence of differential human spinal reflex modulation between young and elderly subjects. Further, these results may point towards the role of presynaptic inhibition in mediating these differences, and may lead to a more complete understanding of the different postural control strategies between young and elderly subjects.

Adult↗