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Biomedical subjects

N Radicheva

Publications and source records attributed to N Radicheva.

35 records · Page 2Linked to original sources
PubMed1986

Intracellular and extracellular action potentials in frog muscle fibre upon blocking the potassium conductivity.

The dependence between intra- and extracellular action potentials of single muscle fibre of Rana ridibunda when 4-aminopyridine is applied for blocking the potassium conductivity of the membrane was investigated. The changes in the intracellular action potential reflect the degree of the blocker's effect. The initial part of this potential remains practically unchanged. A considerable prolongation of the repolarization phase is observed until a plateau-type potential is established. The extracellular action potentials recorded close to the fibre do not manifest substantial changes. Conclusions are reached about the importance of K-currents for the shape of the extracellular action potential shape.

4-Aminopyridine↗
PubMed1986

Effect of the blocked inactivation of sodium channels on intracellular and extracellular action potentials from isolated frog muscle fibres.

The intra- and extracellular action potentials of isolated frog muscle fibres, treated with ATX II for blocking sodium inactivation, are investigated. In concentrations of 0.1 to 0.5 X 10(-6) M, ATX II leads to a considerable change of the repolarization phase of the intracellular potential, with a tendency toward achieving a plateau-type potential. In addition to the intracellular action potentials, extracellular action potentials were also recorded from the same fibres. Immediately next to the fibre membrane and at a small radial distance the extracellular potentials did not manifest essential differences compared with recordings under normal physiological conditions. Conclusions are reached about the influence of the blocked Na-inactivation on the intra- and extracellular action potentials of muscle fibres.

Action Potentials↗
PubMed1986

Effect of short interstimulus intervals on the intra- and extracellular action potentials of isolated frog muscle fibres.

The changes in the time and space derivatives of the intracellular action potentials of isolated frog muscle fibers immersed in hypertonic sucrose-Ringer's solution were studied using paired stimulation with different interstimulus intervals. The peak-to-peak amplitude and the amplitudes of the separate phases of delta V/delta t and delta 2V/delta t2 decreased at intervals shorter than 10.25 ms as the duration of the phases lengthened. The velocity of spreading decreased at intervals below 7-10 ms and increased at longer intervals up to 40-100 ms. The peak-to-peak amplitude and the amplitudes of the separate phases of delta V/delta x and delta 2V/delta x2 decreased at intervals below 40-100 ms. The length of the separate phases of the space derivatives was almost constant. The extracellular action potentials near the membrane were similar to delta 2V/delta x2. When changing the interstimulus intervals the amplitude of the potentials recorded at different radial distances changed almost proportionally. In normal Ringer's solution the extracellular action potentials at different radial distances also changed almost proportionally depending on the intervals. They decreased at the shortest intervals and increased above the level measured at single stimuli for intervals longer than 7-10 ms, but shorter than 40-100 ms.

Action Potentials↗
PubMed1986

Extracellular potential field of excited isolated frog muscle fibres immersed in a volume conductor.

The extracellular potential field of isolated frog muscle fibres immersed in a volume conductor was studied at radial distances up to 3 mm during excitation. The shape of the field distant from both the point of the origin of the excitation and the end of the fibre as well as changes in the field when depolarization wave approached the fibre end were described. Different amplitude decrease rates in individual phases of the extracellular potential and the peak-to-peak amplitude at different temperatures were found. Extracellular potentials at long radial distances were recorded using an averaging technique. The shape of the extracellular potentials at long radial distances over the fibre and beyond its end were very similar to the shape of extraterritorial potentials of a single motor unit.

Animals↗
PubMed1986

Motor unit potentials at high muscle activity recorded by selective electrodes.

The selectivity of different kinds of electrodes for recording of single motor unit potentials was theoretically evaluated. A new type of selective "branched", superficial and subcutaneous wire electrodes was described. The discharge of single alpha motoneurons during movements against elastic resistance was investigated studying motor unit potentials in m. biceps brachii and m.interosseus dorsalis l. Depending on the velocity of the movement, the following pattern of discharge was found: 1) At slow velocity the frequency of discharge increased and new motor units were recruited. 2) At higher velocity the frequency of discharge was constant. The muscle force increased only when new motor units were recruited. 3) At very quick ballistic movements the frequency of discharge decreased during the movement.

Adult↗
PubMed1985

Relations between the shapes of different muscle potentials. Experimental and model investigations.

Intracellular muscle action potentials, the corresponding to them extracellular action potentials recorded at short and long radial distances, extraterritorial motor unit potentials, evoked muscle potentials (M-, H- and T-potentials) and averaged potentials of the summated electromyogram were studied experimentally and compared with the calculated potentials. The similarity in the shape of the different muscle potentials and some second-rate differences were explained taking into account the point of recording, the different degree of desynchronization of the summated potentials and some other factors.

Action Potentials↗
PubMed1978

Discharge frequency of the motor units in human muscles under different stationary isometric tension, investigated by a new method.

A new method has been worked out for selective recording of the impulses of individual MU under high muscular efforts. It is suggested to use the EMG derivatives (the differentiated EMG-DEMG and the double differentiated EMG-DDEMG and possibly the higher derivatives). It was demonstrated that at different stationary isometric tensions the dependence between the discharge frequency and the tension may be linear or non-linear, with a bigger growth at the small efforts and a smaller growth at the big efforts. The inverse non-linearity--sharp rise of the frequency at the high efforts--was not established. Conformation was found for the possibility of distinguishing between two types of MU according to the type of this dependence.

Action Potentials↗
PubMed1977

Motor units activity of dog postural muscles in standing position.

Discharges of separate motor units (MU) of dog muscles are studied in standing position and under conditions of passive stretch and shortening of the muscles. In standing position the average discharge frequency in the fore leg extensors is found to be of the order of 25-30 imp/s. A doublet pattern of firing and recruitment and derecruitment of single MUs over different periods of time is observed. The transient processes of the instantaneous discharge frequency of single MUs are observed upon passive stretch and shortening of the muscles. Different types of transient processes are described, both during recruitment and derecruitment in standing-position, and during the passive changes in muscle length. A dependence is found of the transient processes in the velocity of the passive changes in length and the probably physiological mechanisms of these phenomena are discussed.

Animals↗
PubMed1977

Firing of motor units upon flexion reflex in dogs.

A study is made of the changes in the transient processes of the instantaneous frequency of the discharges of preactive motor units (MU) in dog m. gastrocnemius and m. semitendinosus under conditions of flexion reflex caused by electrical stimulation. Surface electrodes are used to record the activity of the single MUs. Five types of transient processes are described mainly depending on the intensity of stimulation. A stimulus with weaker intensity leads to an increase in the instantaneous frequency of the discharges 60 ms after its application, followed by a decrease and later by a new increase. Inhibition phenomena are observed in cases of higher intensity. The interpretation of these data takes into consideration the mechanisms of recurrent inhibition and the role of some of the afferent inputs of the flexion reflex.

Animals↗
PubMedDate not supplied

Further studies on Nivalin P-induced changes in muscle fiber membrane processes.

Nivalin P, composed of Nivalin (galanthamine hydrobromide) and Pymadin (4-aminopyridine hydrochloride), was applied extracellularly to isolated skeletal muscle fibers during prolonged activity (fatiguing) to better understand the effects of the drug on membrane ionic processes. Changes in intracellular action potential (ICAP) and twitch (Tw) parameters were monitored from treated and untreated fibers during uninterrupted activity (endurance time, ET) produced by repetitive stimulation every 200 msec for 3 min. Nivalin P-induced a shortening of the ET, drastic changes in repolarization of the ICAP corresponding to changes in negative afterpotential and falling area and an initial increase of the Tw amplitude and duration. These results suggest that Nivalin P: (i) inhibits the Na+, K(+)-pump due to nonspecific reduction of Na+ influx, stimulates the Na(+)-Ca2+ exchanger and inhibits K+ conductance; (ii) increases Ca2+ release and delays Ca2+ uptake under sufficient depolarization. It was concluded that fatigue develops faster in the presence of Nivalin P.

4-Aminopyridine↗
PubMedDate not supplied

[Relation between inter- and intracellular action potentials of frog isolates muscle fiber at various temperatures].

Extra- and intracellular action potentials (AP) of isolated muscle fibres plunged into volume conductor were studied at different temperatures. Changes of the first and second AP derivatives and their temperature dependence were described. The changes are explained by temperature effect on the density of input and output ion currents. Changes of the shape of extracellular potential with temperature increase were described. They were concerned with the changes of the first and second AP derivatives and are due to the peculiar distribution of the potential field in the volume conductor around an excitable fibre of the finite length.

Action Potentials↗