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PubMed1991

Effects of the calcium channel agonist, Bay K 8644, on the mechanical output of skeletal muscle fibers.

1. The effects of the calcium agonist, Bay K 8644, on the mechanical output of skeletal muscle were studied in frog semitendinosus fiber bundles and in whole sartorius muscles. 2. Low concentrations of Bay K 8644 (less than or equal to 1 microM) had no significant influence on isometric twitches. Concentrations between 5-20 microM increased peak tension by 28.6 +/- 2.9% while higher concentrations (greater than or equal to 50 microM) initially increased then depressed twitches by 70 +/- 3.5%. 3. 10 microM Bay K 8644 also increased peak tension developed during low frequency stimulation (i.e. less than or equal to 40 Hz), slightly depressed high frequency contractions (i.e. greater than or equal to 80 Hz) but did not reduce maximal tetanic tension which occurred at about 60 Hz. 4. Potentiation of twitches and low frequency tetani and depression of high frequency tetani by Bay K 8644 were partially antagonized by nifedipine (10 microM), low extracellular calcium and D-600 (5 microM). These conditions did not, however, block the depressant actions of greater than or equal to 50 microM Bay K 8644. 5. In skinned fibers, 10 microM Bay K 8644 had no effect on resting or maximal Ca2+ activated tension. Also, 10 microM Bay K 8644 had no effect on caffeine contractures when added to the previous Ca2+ loading solution. 6. These results suggest that Bay K 8644 has both positive and negative inotropic actions on isolated skeletal muscle, which are dependent on drug concentration and muscle activation pattern.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1991

Dihydropyridine effects on skeletal muscle fatigue.

1. The purpose of this investigation was to determine if alterations in extracellular calcium (Ca2+) influx by the dihydropyridine derivatives Bay K 8644 and nifedipine affected skeletal muscle fatigue. 2. Tetanic contractions (80 Hz, 100 msec) of frog sartorius muscles were evoked every sec for 3 min. Muscles were fatigued in normal Ringer's solution (NR), in NR containing 1 microM nifedipine of 10 microM Bay K 8644 or in low Ca2+ Ringer's. 3. In each case, the experimental conditions increased the rate and magnitude of fatigue. Rate constants of fatigue obtained during Bay K 8644, nifedipine and low Ca2+ conditions (-.0122 +/- .0016, -.0397 +/- 0022 and 0.0169 +/- .0064 sec-1, respectively) were significantly greater than NR (-.0104 +/- .0006 sec-1, p less than .05). In addition, tetanic forces developed at the end of the stimulation period under the experimental conditions (3.90 +/- 0.81, 1.21 +/- 1.40 and 2.04 +/- 1.10% of initial) were significantly less than NR (7.18 +/- 1.27%, p less than .05). 4. Caffeine contracture forces (10 mM) evoked immediately after stimulation were not significantly different between conditions. 5. These results suggest that alterations in sarcolemmal Ca2+ exchange has some influence on the fatigue process.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1989

Ultrastructural variations in frog muscles subjected to sciatectomy.

Fine structural variations in two different types of muscles of frog (Rana cyanophlictis) subjected to sciatectomy were studied electronmicroscopically. Gastrocnemius muscle showed marked myofibrillar disarray and degeneration due to sciatectomy, while sartorius muscle was relatively less affected. The extent of sciatectomy induced fine structural variation was in proportion to the degree of denervation atrophy (as reflected by loss of wet muscle weight) in these muscles. Differences in the degree of degenerative changes in atrophying muscles may be attributed to variations in fiber type composition and stretch effects imposed during swimming movements.

Animals↗

PubMed1981

Extrajunctional spread of acetylcholine depolarization on frog skeletal muscle membrane.

1. The extrajunctional spread of end-plate depolarization induced by acetyl) choline (ACh) applied in the bathing solution was studied on frog (Rana esculenta-skeletal muscle fibers. 2. The characteristics of this spread were determined on sartorius muscles mounted in a chamber where the end-plate free pelvic part was separated by a rubber membrane from the end-plate containing tibial one. There was no change in membrane potential if ACh was applied selectively on the pelvic part, even at a concentration of 10 mmol/l. However, on applying 1 mmol/l ACh on the tibial part, depolarization spreading over to the pelvic part was observed. 3. The peak values of ACh depolarization were not modified by tetrodotoxin (TTX) at a concentration of 32 nmol/l, whereas it was decreased by 35% in the presence of 3.1 mumol/l TTX. 4. ACh depolarization measured on the extrajunctional membrane in the presence of TTX is the result of the electronic spread of end-plate depolarization. The length constant of this spread was about the same as the length constant determined by square pulse analysis. 5. When the generation and propagation of action potentials accompanying ACh depolarization were not blocked either by TTX or Na-free Ringer solution, the depolarization values observed on the pelvic part were slightly higher than what could have been expected on the basis of electrotonic behaviour. 6. The above results imply the absence of ACh receptors from the extrajunctional membrane of twitch fibres. Deviations from the electrotonic spread are due to the action potentials accompanying ACh depolarization.

Acetylcholine↗

PubMedDate not supplied

[Repair of a severed nerve with denatured muscle graft--preliminary results of a new surgical technic].

In Neurosurgical Clinic of Military Medical Academy prospective study about the use of denatured muscle graft in nerve repair is in progress, based on numerous experimental and sporadic clinical literature data. The first, experimental part of the investigation is directed to operative technique details and also to find out the manner and duration of muscle denaturation which provide ideal conditions for regenerating axons sprouting. It is concluded that greater pectoral muscle have to be muscle graft donor for nerve defects shorter than 6 cm, and sartorius muscle for those longer than 6 cm. Denaturation for 30 seconds in liquid nitrogen and after that in distilled water for 3 minutes results in micromorphological status in muscle graft which is optimal for axonal regeneration. In the second, clinical part of the work reparations of missile neurotmesis of radial nerve with denatured muscle grafts are performed. Preliminary results 9 months after operation are quite comparable with results after sural nerve graft reparation.

Adult↗

PubMed1996

The effects of cetiedil and its congeners on levcromakalim-stimulated 86Rb efflux from smooth and skeletal muscle.

The effects of cetiedil on levcromakalim-stimulated 86Rb efflux from rat aorta, rat anococcygeus and frog sartorius muscle have been investigated. In experiments on rat aorta, cetiedil inhibited the tracer efflux stimulated by 10 microM levcromakalim with an IC50 of 1.3 +/- 0.4 microM. In the rat anococcygeus and frog sartorius 10 microM cetiedil caused 67 +/- 11% and 84 +/- 4% inhibition of the responses to 10 microM and 50 microM levcromakalim respectively. The effect of two analogues of cetiedil, UCL 1285 (cetiedil methiodide) and UCL 1495 (triphenyl acetic acid-2-N[5-ethyl-2-methylpiperidinoethyl] ester) were also tested on rat aorta. UCL 1285 caused inhibition of the response to 10 microM levcromakalim with an IC50 of approximately 6 microM. In contrast, UCL 1495 (10 microM) had no significant effect. It is concluded that cetiedil is an effective blocker of the action of levcromakalim in smooth and skeletal muscle but does not distinguish between tissues. The relative activities of cetiedil, UCL 1285 and UCL 1495 are discussed in relation to their activity at other cetiedil-sensitive K+ channels.

Animals↗

PubMed1986

The effect of length range on heat rate and power during shortening near in situ length in frog muscle.

Heat rate and tension were measured during the steady state of isovelocity shortening in frog sartorius muscles at two speeds (7.5 and 2.0 mm s-1) through two ranges of the length-tension curve: 1.11 to 1.01 L0 and 1.01 to 0.91 L0. Both heat rate and mechanical power were higher at short length than at long length. The ratio of mechanical power to total energy rate was smaller at short length. The difference in heat rates in the two length ranges was greatest during shortening at 7.5 mm s-1 and least during isometric contractions. Calculations were made for two extreme interpretations of the results, based on the assumption that 30% of the isometric maintenance heat rate at optimum length is produced by processes related to activation: that all the difference in heat rate results from effects of length on activation processes and that all the difference results from effects on contractile processes. The rate of heat production by activation processes would have to be 1.5 times higher at short than at long length in an isometric contraction, 1.7 times higher during shortening at 2mm s-1 and 2.0 times higher at 7.5 mm s-1 to explain the differences in heat rate. The rate of contractile processes would have to be only 1.2 times higher at short than at long length. The results favour the interpretation that the contractile process itself is sensitive to sarcomere length near the plateau of the length-tension curve.(ABSTRACT TRUNCATED AT 250 WORDS)

Actomyosin↗

PubMed2003

Hypotonic stimulation of the Na+ active transport in frog skeletal muscle: role of the cytoskeleton.

Hypotonicity produces a marked activation of the Na+ pump in frog sartorius muscle. The increase in net Na+ efflux under hypotonic conditions occurs despite the reductions in [Na+]i that are due to fibre swelling and Na+ loss. The pump density (ouabain binding) increases not only upon reduction of the medium osmotic pressure (pi) from its normal value (pi = 1) to one-half (pi = 0.5), but also in muscles that are returned to pi = 1 after equilibration in pi = 2 medium. The equilibration in pi = 2 medium does not affect pump density. Ouabain-binding increments cannot be ascribed to a rise in the Na+-K+ exchange rate of a fixed number of pumps: they also occurred in the continued presence of a saturating concentration of ouabain (50 microM). Under those conditions, the pi = 1 pi = 0.5 transfer produced a 43 % increase in pump sites, while the pi = 2 pi = 1 transfer induced a rise of 46 %. Actinomycin D did not alter the stimulation of Na+ extrusion elicited by hypotonicity, suggesting that de novo synthesis of pumps was not involved in the increase of the apparent number of pump sites. Disruption of microtubules by colchicine (100 microM) and intermediate filaments by acrylamide (4 mM) did not alter the hypotonic effect. Likewise, genistein (100 microM), a specific inhibitor of tyrosine kinase, did not affect significantly the hypotonic response. Microfilament-disrupting agents like cytochalasin B (5 microM) and latrunculin B (10 microM) reduced the increase in Na+ efflux induced by pi = 1 pi = 0.5 transfer by about 35 % and 72 %, respectively. Latrunculin B reduced the increases in pump density generated by pi = 1 pi = 0.5 and pi = 2 pi = 1 transfers by about 79 % and 91 %, respectively. The results suggest that the membrane stretch due to hypotonic fibre volume increase would promote a microfilament-mediated insertion of submembranous spare Na+ pumps in the sarcolemma and, consequently, the rise in active Na+ transport.

Actins↗

PubMed1987

Effects of phlorizin and phloretin on passive and dynamic electrical properties in muscle membrane.

The effects of phlorizin and phloretin on the cable properties were investigated in frog sartorius muscle by conventional cable analysis. Actions of phloretin on voltage-dependent ionic conductances were also studied by analysis of the phase plane trajectories. Both drugs evoked a significant decrease in specific membrane resistance (Rm) in chloride-containing Ringer's solution. The linear membrane capacitance increased by about 30%. On the contrary, in the presence of the non-penetrating anion, glutamate, a slight increase in Rm was induced by phlorizin. It is suggested that these drugs may increase the chloride conductance in the muscle membrane. Under the effect of phloretin the resting membrane potential remained unchanged but the amplitude of the action potential was lowered and the rate of repolarization was significantly reduced. The rate of depolarization during the "foot" of the action potential and the conduction velocity calculated from the rate constant of depolarization decreased. The maximum Na conductance was not altered by phloretin but K conductance was reduced. The time constant (tau K) reflecting the kinetic properties of K conductance was increased about seven-fold. It is suggested that great importance may be attributed to the dipole properties of these drugs in the actions presented above.

Action Potentials↗

PubMed1981

ALlometric growth of histochemical types of muscle fibers in ducks.

Radial growth (fiber cross sectional area) was measured at the midlength of sartorius muscles in Pekin and Muscovy breeds of domestic ducks. Pekins exhibited faster early growth (up to 7 weeks after hatching) while Muscovies exhibited greater divergence between sexes (after 7 weeks). In both sexes of both breeds, radial growth of strong-ATPase fibers failed to keep pace with that of weak-ATPase fibers; allometric growth ratio, k = 0.64 in Muscovy males, k = 0.65 in Muscovy females, k = 0.61 in Pekin males and k = 0.61 in Pekin females (P less than 0.005). At 7 weeks, strong-ATPase fibers showed a greater range in their potential for aerobic metabolism, as judged by cytophotometry of their reactions for succinate dehydrogenase (SDH). Thus, in strong-ATPase fibers, cross sectional area was inversely related to SDH reaction in both Pekin and Muscovy breeds (r = -0.76 and r = -0.43, respectively). Further evidence was found for developmental changes in muscle structure caused by changes in relative fiber length, as proposed by MacCallum in 1898.

Adenosine Triphosphatases↗

PubMed1994

Negative developed tension in rapidly shortening whole frog muscles.

High speed isovelocity shortening using a servo-controlled lever was performed on isolated whole frog sartorius muscles at long lengths to ensure substantial passive tension. The tension records of unstimulated control experiments were subtracted from the tension records of fully-tetanized experiments on the same muscles to yield the developed tension exerted by the contractile proteins alone. There are several main results: (1) the positive developed tension had the same relation with shortening speed observed by other researchers in single fibres with no passive tension present; (2) negative developed tension was always measured at velocities of shortening above Vmax, where Vmax (typically 1.5 muscle-lengths s-1 at 2 degrees C) is defined as the velocity of shortening observed to yield zero developed tension; (3) negative developed tension was roughly asymptotic to -0.05 T(o), where T(o) is the developed isometric tetanic tension for the muscle length at which the developed tension was measured during steady shortening; (4) negative developed tension diminished in magnitude at velocities of shortening above approximately 2.5 Vmax; (5) a 10 degrees C increase in temperature from 2 degrees C to 12 degrees C had no significant effect on the shape of the normalized force-velocity curve (%T(o) versus %Vmax), but did increase Vmax by a factor of 2.6 in agreement with the results of previous studies measuring Vmax in the absence of passive tension; (6) addition of curare in the saline bath did not affect the results.

Animals↗

PubMed1976

Effects of cytochalasin B on the electrical activity of frog muscle fibers.

Cytochalasin B (50 mug/ml) markedly prolonged the falling phase of the action potential in frog sartorius muscle fibers without any effect on the rising phase and the amplitude of the action potential, nor on the resting potential. The maximum rate of fall of the action potential was reduced from 173 to 133 V/sec. The early depolarizing after-potential was increased in amplitude and lasted for as long as 1 sec. These changes in the falling phase of the action potential appear to be due to a slowing of sodium inactivation. Potassium conductance increase was not appreciably affected. The muscle treated with cytochalasin B responded to nerve stimulation with repetitive discharges which originated in presynaptic nerve elements.

Action Potentials↗

PubMed1993

Notexin-induced muscle injury in the dog.

Notexin, a myotoxic phospholipase, was used to induce focal necrosis in the sartorius muscles of normal mixed-breed adult dogs and in 12-week-old beagles. Notexin injury caused pathologic changes similar to those of Duchenne muscular dystrophy (DMD) and its canine homologue, golden retriever muscular dystrophy (GRMD). All three conditions are characterized by increased serum creatine kinase (CK) levels, sarcolemmal defects, delta lesions, hyaline degeneration of myofibers, calcium-positive myofibers, and minimal effects on neurovascular structures. Four and 24 h after exposure to notexin, serum CK levels were elevated, and many myofibers were necrotic. In addition, by 24 h the necrotic areas were heavily invaded by mononuclear cells, and calcium-positive myofibers were prominent. Capillaries appeared intact even in areas of marked myonecrosis. Massive cellular infiltrate and myotube formation was evident at 3 days post injury. By 7 days, most affected fascicles were occupied by small immature myofibers. Regeneration was largely complete at 21 days. Our results suggest that notexin-induced muscle injury in dogs will be useful in the evaluation of potential therapies for DMD such as myoblast transplantation.

Animals↗

PubMed1986

Blockage of resting potassium conductance in frog muscle fibers by a toxin isolated from the sponge Haliclona viridis.

A fraction able to irreversibly depolarize sartorius muscle fibers was isolated from the marine sponge. The resting potential is decreased from -84 (-85, -83) mV (median and its 95% confidence interval) to -40 (-46, -30) mV. The fibers depolarized by the sponge toxin are restored to -54 (-57, -49) mV when external sodium is replaced by Tris or to -52 (-57, -47) mV when calcium is removed from the saline solution in the presence of 1 mM EDTA and 1 microM tetrodotoxin. Tetrodotoxin alone (1 micron) has no effect on the depolarization [-43 (-50, -37) mV] produced by the sponge and 5 mM manganese only repolarizes the fibers to -48 (-55, -40) mV. The depolarization is potentiated [-28 (-33, -23) mV] when chloride is replaced by glutamate in the external solution. The access resistance of the muscle fibers is not significantly changed from its control value of 2.74 (2.28, 3.30) M omega when toxin is added. By contrast 20 mM K+ superfused to the fibers changes membrane potential to -44 (-46, -42) mV and decreases access resistance to 1.99 (1.38, 2.87) M omega. The toxin is devoid of any effect on the endplate, since the depolarization of the postsynaptic membrane is identical to the extrajunctional area, and miniature endplate potentials of normal shape and high frequency are easy to record from toxin treated fibers. The action potential is not modified by the toxin. The toxin is a small polar compound insoluble in acetone and is likely to act on a receptor located on the outer phase of the membrane. The biological activity appears as a peak on elution with 1 M acetic acid on Bio Gel P2.

Animals↗

PubMed1991

Differential effects of temperature on contractile behavior in isolated frog skeletal muscle.

1. The thermal dependence of contractile behavior at different stimulation frequencies was investigated in isolated frog sartorius muscles. 2. Increasing incubation temperature (10-30 degrees C) produced decreases in Pt (43.7%) and P15 (70.3%), and an increase in Po (26.0%). 3. Thermal ratios (R10) calculated for Pt, P15 and Po indicated high thermal dependence at lower temperatures (10-20 degrees C; 0.60, 0.44 and 1.38, respectively) but relative thermal independence at higher temperatures (20-30 degrees C; 0.95, 0.75 and 0.95, respectively). 4. Contractile ratios (Pt/Po and P15/Po) decreased with increased temperature (10-30 degrees C; 56.3% and 76.0%, respectively). 5. Thermal ratios (R20) calculated for peak tension at different stimulation frequencies demonstrated high thermal dependence at the lower frequencies (10-30 pps, 0.46-0.48) and decreasing dependence at higher frequencies (40-50 pps, 0.69-0.82).

Animals↗

PubMed1987

X-ray diffraction evidence for the existence of 102.0- and 230.0-nm transverse periodicities in striated muscle.

Synchrotron radiation techniques have enabled us to record meridional x-ray diffraction patterns from frog sartorius muscle at resolutions ranging from approximately 2,800 to 38 nm (i.e., overlapping with the optical microscope and the region normally accessible with low angle diffraction cameras). These diffraction patterns represent the transform of the low resolution structure of muscle projected on the sarcomere axis and sampled by its repeat. Altering the sarcomere length results in the sampling of different parts of this transform, which induces changes in the positions and the integrated intensities of the diffraction maxima. This effect has been used to determine the transform of the mass projection on the muscle axis in a quasicontinuous fashion. The results reveal the existence of maxima arising from long-range periodicities in the structure. Determination of the zeroes in the transforms has been used to obtain phase information from which electron density maps have been calculated. The x-ray diffraction diagrams and the resulting electron density maps show the existence of a series of mass bands, disposed transversely to the sarcomere axis and distributed at regular intervals. A set of these transverse structures is associated with thin filaments, and their 102.0-nm repeat suggests a close structural relationship with their known molecular components. A second set, spaced by approximately 230.0 nm, is also present; from diffraction theory one has to conclude that this repeat simultaneously exists in thick and thin filament regions.

Animals↗

PubMed1960

The movement of thallium ions in muscle.

Measurements have been made of the fluxes of thallous ions (Tl(+)) across the membrane of frog sartorius muscle fibers. These show that at an external concentration of 74 microM the influx is about 270 x 10(-15) moles/cm.(2) sec., while the efflux from a muscle with an internal concentration equal to the above is 5 x 10(-15) moles/cm.(2) sec. The efflux is increased of the order of 300-fold during a muscle twitch, and Tl(+) reach a steady-state distribution between fiber water and Ringer solution that is very close to the corresponding ratio for K(+). High concentrations of Tl(+) depolarize the membrane about 58 mv. for a tenfold increase in external concentration. The results obtained are consistent with the view that the muscle fiber membrane cannot distinguish between the toxic heavy metal Tl(+) and K(+), provided that the concentrations of the former ion are kept low. High concentrations of Tl(+), if allowed to act for an appreciable period of time, lead to irreversible damage to muscle.

Animals↗

PubMed1964

THE RELATION BETWEEN THE LATE AFTER-POTENTIAL AND THE SIZE OF THE TRANSVERSE TUBULAR SYSTEM OF FROG MUSCLE.

This is an investigation of the effects on the late after-potential of immersing frog sartorius muscles in three kinds of modified Ringer's fluid; hypertonic, low chloride, and potassium-free. The late after-potential has been attributed to the depolarizing effect of an accumulation of potassium, during a preceding train of impulses, in the intermediary space of the model of a muscle fiber proposed by Adrian and Freygang. Both the hypertonic and low chloride solutions prolonged the late after-potential reversibly and the potassium-free solution shortened it. The effect of the low potassium solution fitted those data calculated from the model, but the effect of the hypertonic and low chloride solutions required an increase in size of the intermediary space of the model in order to fit the calculated data. An electron microscopic study of the muscles showed that the size of the transverse tubular system changed reversibly in the hypertonic and low chloride solutions in almost the amount necessary to fit the experimental data to the calculated data. This agreement between the change in size of the transverse tubular system and that of the intermediary space indicates that the intermediary space may be the transverse tubular system.

Animals↗