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Biomedical subjects

R Rüdel

Publications and source records attributed to R Rüdel.

153 records · Page 9Linked to original sources
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Clinical study of paramyotonia congenita with and without myotonia in a warm environment.

Fourteen patients with paramyotonia congenita were examined clinically. Patients of 3 families had no myotonia in a warm environment while in a cold environment they developed paradoxical myotonia (myotonia aggravated by repeated muscle contraction). Patients of a 4th family had myotonia associated with after-activity in a warm environment which was not paradoxical. This myotonia was aggravated by cooling. In a warm environment the resting muscles of all patients showed no spontaneous electromyographic activity except for occasional myotonic runs. On cooling, spontaneous fibrillations developed. This was most intense at 32 degrees C-28 degrees C (muscle temperature). On deeper cooling it ceased. In contrast, 5 patients with myotonia congenita did not show such activity during cooling. In all paramyotonic patients cooling (30 degrees C-25 degrees C) produced muscle paralysis, which outlasted rewarming by several hours. At 32 degrees C-30 degrees C muscle relaxation was slowed. Recording of electromyographic activity and isometric contractions of the long finger flexors during cooling revealed that the slowing of muscle relaxation in paramyotonia is not as closely linked to after-activity as is the slowing of muscle relaxation in myotonia congenita.

Adolescent↗
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Membrane defects in paramyotonia congenita with and without myotonia in a warm environment.

Three patients with paramyotonia congenita and 3 control persons were biopsied for an in vitro investigation of the sarcolemmal membrane parameters and of the contractile properties of paramyotonic muscle. At 37 degrees C, paramyotonic muscle fibers had normal resting potentials, but on cooling to 27 degrees C they depolarized. Depolarization to -60 mV caused spontaneous activity, and further depolarization to -40 mV caused inexcitability. Depolarization could be prevented by the application of tetrodotoxin, a finding suggesting a defect in the Na channels. Analysis of the membrane current densities using voltage clamps with 3 microelectrodes revealed that in paramyotonic patients at 37 degrees C all component conductances were normal, except for a decreased Cl conductance in the patient who had myotonia in a warm environment. At 27 degrees C, the Na and Cl conductances were abnormally high. The K conductance was always normal. The results explain the clinical symptoms of weakness and paralysis. Potassium- and caffeine-contracture experiments gave normal results. The clinical symptom of paramyotonic stiffness, therefore, has not been explained by these studies.

Action Potentials↗
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Membrane currents in human intercostal muscle at varied extracellular potassium.

Hyperpolarizing and depolarizing square steps were imposed on the membrane potential of excised human intercostal muscle fibers by means of a 3-microelectrode voltage clamp. The steady-state amplitudes of the membrane currents inducing such steps were investigated as a function of the membrane potential, while the muscle was bathed in solutions varying in potassium content (Ke = 1, 3.5, 7, 20, and 60 mM). At all potassium concentrations, the membrane acted as a rectifier, both in the inward- and outward-going directions. Inward currents were much reduced when Ke was lowered from 3.5 to 1 mM, and were increased when Ke was raised beyond 3.5 mM. The delayed outward current was reduced when Ke was increased from 3.5 mM to 7 mM and higher potassium concentration. The results were qualitatively similar to those reported for rat skeletal muscle.

Cell Membrane↗
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Excitatory sodium currents of NH15-CA2 neuroblastoma x glioma hybrid cells are differently affected by interleukin-2 and interleukin-1beta.

The neuroblastoma x glioma hybrid cell line NH15-CA2 was used to test the effects of two interleukins on neuronal Na+ channels. The cells were cultured in the presence of dibutyryl cAMP and retinoic acid, which yielded a high expression of Na+ channels so that the cells were excitable. Na+ currents were triggered and recorded in the whole-cell recording mode. Comparison of the effects of tetrodotoxin and mu-conotoxin established that the expressed Na+ channels were of the neuronal type. Bath-applied recombinant human interleukin-2 (rIL-2) had a reversible inhibitory effect on the Na+ currents, although to a lesser extent than on muscular Na+ currents (more than 1000 U/ml required for 50% block in NH15-CA2 cells vs 500 U/ml in myoballs). The current/voltage relationship was not affected by the presence of rIL-2, but the steady-state inactivation curve was shifted by -7.7 +/- 4.8 mV (mean +/- SD, n=18). Recombinant human interleukin-1beta (rIL-1beta), applied at 1000 U/ml, showed an inhibitory effect on the Na+ currents in about one-third of the cells tested. The mechanism of inhibition was different from that of rIL-2, as rIL-1beta seemed to cause a block without affecting voltage dependence or kinetics of the channels.

Animals↗
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Sodium-potassium movement and the regulation of cardiac muscle activity.

The changes in intracellular sodium activity and contractility produced by short-lasting application of a fast-acting cardiac glycoside were measured in guinea-pig ventricular muscle. It was found that under certain conditions the change in twitch tension paralleled the change in sodium activity. It is suggested that the electrogenic sodium pump may be involved in the regulation of both the mechanical and the electrical activity of cardiac muscle.

Animals↗