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Biomedical subjects

S Muchnik

Publications and source records attributed to S Muchnik.

At least 55 records · Page 3Linked to original sources
PubMed1985

Frequency-dependent effect of verapamil on rat soleus muscle.

In the presence of verapamil (0.1 mM) rat soleus muscle fibers failed to generate action potentials with overshoots. In fibers with their Vm set to a local level of -90 mV, verapamil produces a gradual reduction in the amplitude of the repetitive action potentials; this effect is more pronounced at high rates of stimulation (100 Hz). Our results suggest a local anesthetic action of this drug that could contribute with its calcium channel blocking effect to the diminished mechanical tension observed in the presence of the drug.

Action Potentials↗
PubMed1985

Influence of trophic substances in the regulation of resting membrane potential and ionic concentration in skeletal muscle.

We studied the ionic and water content and the resting membrane potential of rat extensor digitorum longus EDL muscles at different times after unilateral nerve crush. Intracellular potassium concentration decreased progressively during the 1st week after nerve crush whereas intracellular sodium concentration increased significantly. At about day 10, when functional reinnervation (presence of end-plate potentials and miniature end-plate potentials) was detected, the above changes tended to return to control values. In addition, there was a significant difference between muscles with long and short nerve stumps. These results suggest a neurogenic dependency of muscle hydroelectrolytic composition. The decrease in resting membrane potential was greatest after 6.5 days of denervation when changes in the internal ionic concentration were maximum; however, these ionic changes contributed little to the decrease. The recovery of the resting membrane potential commenced at least 48 h before the first signs of functional reinnervation (10th day). This finding suggested an important contribution of some neurotrophic material in early stages of the reinnervation when nerve-muscle contacts were already established. Later, the contribution of mechanical activity to the restoration of the RMP became apparent (20th day); fibrillation potentials had disappeared by that time.

Animals↗
PubMed1978

Reversible effect of dantrolene sodium on twitch tension of rat skeletal muscle.

The effect of dantrolene sodium on twitch tension in skeletal muscle of the rat was studied in short- and long-term experiments. The twitch tension is reduced to 50% of the control values within 20 to 30 minutes of drug administration. The recovery phase is considerably slower than the effect observed on the addition of dantrolene sodium, having a half time of 10 hours. Twenty-four hours after the drug injection, the twitch tension in the treated muscles is indistinguishable from that in the controls. It is shown that the reduction in the magnitude of the twitch produced by dantrolene sodium is slowly and completely reversible.

Animals↗
PubMed1978

Tetrodotoxin blocks mechanical response in mammalian muscle in the presence of tetrodotoxin-resistant action potentials.

The effect of tetrodotoxin (TTX) (10(-5)-10(-6)M) on the mechanical activity and on the action potential of innervated and denervated muscle of the rat was studied. The twitch tension was reduced to 10 % of the control values within 20 min of TTX 10(-6) introduction. This effect was reversible. The mean twitch tension in the presence of 10(-6)M TTX expressed as a percentage of control was 9.3 +/- 2.4 (SEM) for innervated muscle and 10.9 +/- 2.5 for denervated muscle. The dose-effect twitch relation for denervated muscles was not significantly different from that observed in control innervated muscles in the 10(-3)-10(-6) TTX range. Action potentials of innervated muscles could not be elicited in 10(-6)M TTX. In the presence of this (TTX) fibers of chronically denervated muscles consistently responded to stimulation with action potentials which were slower and smaller but still with overshoot, contrasting with fibrillation potentials that had been described to be blocked by TTX.

Action Potentials↗
PubMed1976

Characteristics of reinnervation of skeletal muscle in the rat.

Both extra and intracellular fibrillation activity recorded in vivo was studied during nerve-muscle reinnervation, in control rats and in rats treated with actinomycin D. The study was performed at different times after nerve crushing. End-plate potentials (EPP's) and muscle action potentials were always present on the eleventh day after denervation. Fibrillation activity recorded extracellularly began to decrease on the twelfth day. Intracellular fibrillation activity was found in single muscle cells simultaneously with evoked EPP's muscle action potentials. In early stages of reinnervation two EPP's were recorded in a single muscle cell, thus indicating double innervation. When presynaptic action of actinomycin D was tested no changes were found in miniature end-plate potential frequency. Muscles from rats submitted to early treatment with actinomycin D did not show any delay in the onset of reinnervation. In muscles from rats submitted to late treatment, extrasynaptic sensitivity to acetylcholine was ascertained regardless of the presence of functional reinnervation. Chronic stimulation of denervated muscles, while suppressing fibrillation activity, did not interfere with reinnervation. The results reported suggest that reinnervation can take place independently of fibrillation activity as well as of extrasynaptic receptors.

Animals↗