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Biomedical subjects

R Rüdel

Publications and source records attributed to R Rüdel.

At least 127 records · Page 7Linked to original sources
PubMed1980

Efficiency of light diffraction by cross-striated muscle fibers under stretch and during isometric contraction.

When light is diffracted by a single frog muscle fiber the intensities I kappa of the different orders kappa (kappa = 1,2,3) strongly depend on the angle between the axis of the incident beam and the fiber axis. Maximum intensity is not obtained with perpendicular incidence (omega = 0 degree) but at angles that can be calculated for each order number and sarcomere length using Bragg's formula. In analogy to techniques developed for x-ray structure analysis of mosaic crystals we have rotated the fiber around an axis perpendicular to the fiber axis and to the incident beam axis within an angular range delta omega = +/- 35 degrees and recorded the light intensities I kappa. Diffraction efficiencies defined as E kappa = integral of I kappa d omega were studied as a function of sarcomere length and during isometric contraction. The sarcomere length dependences of the efficiencies E kappa of the first three orders show characteristic trends. E1 increases with fiber stretch, E2 has a minimum at a sarcomere length near 2.8 micrometers, and E3 has a maximum near 2.5 micrometers. These trends as well as the observed efficiency ratios are in fairly good agreement with predictions by the intensity formula developed for x-ray structure analysis. During isometric contraction, the diffraction efficiencies of the fiber decrease, with the decreases becoming greater the higher the order number. These decreases might be caused by a longitudinal displacement of myofibrils of up to 0.4 micrometers. The efficiency of light diffraction strongly depends on the tonicity of the bathing fluid. Hypertonic (3/2 x normal) solution reduces E1 to less than half, hypotonic (2/3 x normal) solution increases E1 to almost twice the value obtained in normal Ringer's solution.

Animals↗
PubMed1979

Corticosteroids and neuromuscular transmission: electrophysiological investigation of the effects of prednisolone on normal and anticholinesterase-treated neuromuscular junction.

The effect of prednisolone on indirectly stimulated rat muscle twitch was investigated at normal and prostigmine-treated neuromuscular junctions. In vivo, predenisolone up to 150 mg/kg body weight did not affect twitch contraction in normal animals. In neostigmine-pretreated animals, however, doses between 12.5 and 90 mg/kg could entirely abolish the anticholinesterase-induced twitch augmentation. In vitro, prednisolone produced a depressant effect on the twitch of a normal phrenic nerve diaphragm preparation which could amount to 20%. When the preparation was pretreated with neostigmine the augmented twitch could be depressed by 10(-3) to 10(-6) mol/l prednisolone to levels below the untreated control. Part of this effect is owing to a suppression of the neostigmine-induced, stimulus-bound repetitive firing of the motor nerve terminals, but to explain the full effect a further inhibitory action on neuromuscular transmission must be assumed. The latter could be accounted for by a depolarizing interaction of prednisolone and neostigmine on the nerve terminals resulting in conduction block. An action of prednisolone on postsynaptic receptors could also be considered. Such effects of the glucocorticoid might contribute to the exacerbation of muscular weakness occasionally observed in patients with myasthenia gravis at the beginning of steroid therapy.

Animals↗
PubMed1979

Interpretation of light diffraction by cross-striated muscle as Bragg reflexion of light by the lattice of contractile proteins.

1. The diffraction spectrum obtained by illuminating a cross-striated muscle fibre with a narrow beam of monochromatic light generally shows asymmetry of light intensity between left and right spectral lines. 2. The asymmetry of light intensity in left and right spectral lines is reversed when the fibre is rotated by 180 degrees. This indicates that intensities of the spectral lines are determined more by Bragg reflexion than by simple diffraction as in a plane grating. Populations of myofibrils with differing tilt of lattice planes must exist in each illuminated fibre segment to account for simultaneous Bragg reflexion to the left- and right-hand sides. 3. The light intensity of spectral lines shows a complicated dependence on the angle at which the incident beam is directed against the fibre. This 'intensity distribution' seems to reflect the specific myofibrillar arrangement at the site of illumination. 4. The intensity distributions of the left and right first order lines show close correlation if the deflexion of the incident beam differs by twice the Bragg angle. 5. The deflexion angle of the incident beam at which maximum intensity in spectral lines is obtained depends on sarcomere length as predicted by Bragg's formula. 6. Intensities of the first and second order lines are little correlated when recorded at the same beam deflexion, but are well correlated when recorded at beam deflexions calculated from Bragg's formula. 7. When a diffraction line is scanned perpendicularly to the meridional plane, the light intensity shows fluctuations resembling those obtained by beam deflexion within the meridional plane.

Animals↗
PubMed1979

Effects of potassium depletion and insulin on resting and stimulated skeletal rat muscle.

The electrophysiological and metabolic responses to insulin of skeletal muscles from control and potassium-depleted rats were compared. Membrane potentials, action potentials, contraction parameters as well as oxygen uptake were measured in diaphragm strips or intact extremity muscles from the two groups, and similar measurements were made in vivo. The muscles were examined in solutions with normal potassium concentration [K]o , reduced [K]o, and in normal [K]o and in normal [K]o with ouabain, in each case before and after insulin, 400 mU/ml. In normal solution, the depleted muscle contractions were weaker and slower than control. The depleted muscles, already having low potassium conductance, are paralysed by the further reduction of potassium conductance after insulin. Hyperpolarising effects of insulin-induced Na/K pumping are offset in the depleted muscles with a high sodium conductance and low [K]o. Respiration is about normal at rest in depleted muscles, despite increased [Na]i, suggesting that the sodium is sequestered. After insulin, reduction of [K]o, or ouabain plus insulin, the depleted fibres take up more O2 than controls. In the presence of ouabain, this respiratory stimulation is believed to represent response to Ca++ influx. The K-depleted rat does not seem to be an entirely satisfactory model of the human disease hypokalaemic periodic paralysis.

Action Potentials↗
PubMed1979

Effects of tocainide on normal and myotonic mammalian skeletal muscle.

The effects of the lidocaine derivative 2-amino-2',6'-propionoxylidide hydrochloride (tocainide, W-36095) on the contraction force and on membrane resting and action potentials of rat diaphragm were tested in vitro. In a concentration of 5 x 10(-4) mol/l, tocainide reduced the amplitude of the twitch by about 25% within 15 min. This reduction was reversible on washout of the drug. Tocainide had little effect on the membrane resting potential, but considerably affected the action potential: rate of rise, maximum amplitude and rate of fall were reduced, the duration increased. The conduction velocity of the action potential was reduced by 20%. Experimental myotonia produced in excised diaphragms or in anesthetized whole animals by anthracene-9-carboxylic acid was completely abolished by low doses of tocainide.

Action Potentials↗
PubMed1978

A diffractometer using a lateral effect photodiode for the rapid determination of sarcomere length changes in cross-striated muscle.

A simple method is devised to record rapid sarcomere length changes of muscle fibres using a lateral effect diode. In the standard position the diffractometer records length changes between 1.65 and 3.8 micron, the output being linear 1 V/micron with a frequency response of -3 dB at 1.2 kHz. The absolute error is less than 0.05 micron between 1.65 and 2.80 micron and less than 0.1 micron between 2.81 and 3.30 micron. The resolution of length changes is less than 0.005 micron over the whole range. By varying the detector position the length range can be extended to either side, and spatial resolution can be improved at the expense of length range.

Histological Techniques↗
PubMed1978

Calcium transients in isolated amphibian skeletal muscle fibres: detection with aequorin.

1. Single twitch muscle fibres isolated from frogs and toads were microinjected with the Ca2+-sensitive bioluminescent protein aequorin. The fibres contracted normally and emitted flashes of light (aequorin responses) in response to stimulation for many hours thereafter. 2. No luminescence was detected from healthy fibres at rest. 3. The aequorin diffused from the site of injection at a rate consistent with a diffusion coefficient of 5 x 10(-8) cm2/sec. 4. During trains of isometric contractions there was a progressive reduction in both the amplitude and the rate of decline of the aequorin response, an observation consistent with the theory that Ca is redistributed from sites of release to sites of sequestration under such circumstances. 5. In isometric tetani light emission continued to rise long after the plateau of force had been achieved. This and the fact that the amplitude of the tetanic aequorin response increased steeply with increasing stimulus frequency suggest that in tetani the sarcoplasmic [Ca2+] may normally be above the level required to saturate the contractile apparatus. 6. Both in twitches and in tetani the amplitude of the aequorin response increased slightly and then decreased substantially as the fibre was stretched progressively beyond slack length. 7. In potassium contractures the luminescent and mechanical responses first became detectable at about the same [K+], but for equivalent force luminescence was less intense than in twitches. The aequorin response was biphasic in solutions of high [K+]. 8. Exposure of the fibre to Ca2+-free solutions had no influence on either the mechanical or the luminescent responses in twitches. In Ca2+-free solutions tetanic aequorin responses tended not to be maintained as well as normally, suggesting that intracellular Ca stores do become somewhat depleted. 9. In twitches the amplitude of the aequorin response probably reflects the amount of Ca2+ liberated into the cytoplasm rather than a [Ca2+] in equilibrium with the myofilaments. Changes in the rate of decay of the aequorin response may reflect changes in the rate of Ca sequestration by the sarcoplasmic reticulum. 10. In K+-contractures and during the plateaus of tetani the aequorin signal changes slowly enough so that it seems unlikely that substantial gradients of [Ca2+] exist at the sarcomere level. Under such circumstances the amplitude of the aequorin response probably does reflect the [Ca2+] in equilibrium with the myofilaments.

Aequorin↗
PubMed1975

Clinical and electrophysiological observations in patients with myotonic muscle disease and the therapeutic effect of N-propyl-ajmalin.

Six patients with congenital myotonia and 4 patients with myotonic dystrophy have been examined clinically before and after the administration of N-propyl-ajmalin, an alkaloid frequently used as a cardiac antiarrhythmic drug. All patients but one reported a good to moderate improvement of their myotonic muscle stiffness. This was verified by measuring the time the patients needed to ascend a flight of stairs and by recording the speed of opening the hand. The amplitude of the compound muscle action potential decreased during repetitive nerve stimulation in myotonic patients. This decrease was not influenced by N-propyl-ajmalin. It seems to be due to the increased after-depolarization observed in myotonic fibres which causes partial inactivation of the Na-carrying system. From one patient a muscle biopsy was taken and intracellular potentials were measured with a microelectrode. Almost all muscle cells investigated showed myotonic activity which was completely abolished by addition of 10(-5) g/ml N-propyl-ajmalin to the bathing fluid. The development and duration of "warm-up" is illustrated and a possible electrophysiological basis is discussed.

Action Potentials↗
PubMed1975

Calcium transients in amphibian muscle.

The calcium-sensitive bioluminescent protein aequorin has been microinjected into isolated amphibian twitch muscle fibers in order to detect the intracellular calcium transients associated with excitation-contraction coupling. While it is not yet possible to make quantitative estimates of the changes in calcium concentration involved, it is possible to detect substantial changes in intracellular calcium transients resulting from changes in temperature, stimulation frequency, fiberlength, and the osmotic strength of the bathing medium.

Aequorin↗