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G A Nasledov

Publications and source records attributed to G A Nasledov.

At least 19 recordsLinked to original sources
PubMed1999

Development of muscle-specific features in cultured frog embryonic skeletal myocytes.

To study the development of muscle-specific features during myogenesis, we analysed the ultrastructure and voltage-dependent currents of frog embryonic skeletal myocytes maintained in culture for 10 days. The cells were maintained under culture conditions that prevented cell division, fusion and cell contacts with neuroblasts. The cell surface was estimated morphometrically and from cell capacity and the values obtained were used to calculate ion current densities. It was shown that the expression of all main types of voltage dependent ionic currents occurs during the first 3-5 days. Na+ maximum specific conductance at days 1-2 was low but by day 7 it showed a 20-fold increase. The magnitude of Na+ current densities increased 16-fold from day 1 (3.6 microA/cm) to the day 7 (58.1 microA/cm). The maximum specific K+ conductance increased almost 3-fold during the first 5 days. In contrast to the other types of currents, I(K) undergoes qualitative changes. Sodium action potentials, whose amplitude and time course depend on gNa/gK ratio, appeared from day 4 in culture, when myofibrils and the T-system also developed. The amplitude of DHP-sensitive slow I(Ca) increased in parallel with the development of the T-membrane. I(Ca,S) density per unit of T-membrane area reached an equilibrium of ca., 17 microA/cm2 on the day 4 and then remained stable until the end of the period of observation. These studies demonstrate that muscle-specific characteristics including morphology and excitatory properties begin to develop on the third day and resemble those of adult muscle cells by the sixth day in culture.

Actin Cytoskeleton↗
PubMed1999

[Inward rectifier potassium current in the frog embryonic skeletal myocytes].

Pharmacological and kinetic properties of the inward rectifier potassium current Iir the frog embryonic skeletal myocytes were found to be identical to those of adult frog skeletal muscle fibres. The data obtained suggest that the Iir plays the main role in maintaining the myocytes resting membrane potential (RMP) when chloride conductance is insignificant. Changes of the integral conductance Gir and the RMP values correlated with the T-system development. The inward rectifier K+ channels, from the early stages of the muscle seem to be located in the T-tubule membranes.

Animals↗
PubMed1998

[Structural differentiation of dissociated skeletal embryonal myocytes of frog under conditions of cell culture].

The development of membrane structures, providing E-C coupling, and the contractile apparatus organization were investigated in frog skeletal myocytes cultured for 1 to 10 days in conditions preventing both myocyte division and fusion. Ruthenium red was used to determine the membranous structures being in contact with the extracellular environment. The marked membrane structures (vesicles and short tubules) appeared to be near the cell membrane on the first days of culturing. The increase in the ratio of the surface area of all internal membranous structures, marked by Ruthenium red, to the external membrane area with aging was proven by morphometric calculations, that means a progressive development. Contractile filaments were found near the cell membrane on the first days of development. Bundles of filaments with initial signs of sarcomere organization were observed on the 3rd-4th days, and myofibrils with highly organized sarcomeres occupied the main part of the sarcoplasm on the 6th day of culturing. The triads appeared also on the sixth day, being regularly inserted into the sarcomere structure. Degenerative signs in the myocytes (sarcomere disorganization and T-tubule swelling) were observed on the 8-10th days, but the area occupied by contractile elements was increased. These results show that the myocyte fusion into myotubules is not a necessary condition for either sarcomere formation, or the formation of all membranous structures providing the E-C coupling.

Animals↗
PubMed1997

[The formation of electrical excitability in cultured frog embryonic myocytes].

Quantitative changes of sodium and potassium ionic currents were studied in the frog embryonic skeletal myocytes cultures under conditions preventing cell fusion and division. During 7 days of culturing the mean values of the sodium and potassium currents densities were 7- and 1.8-fold increased, resp. In currents clamp records the APs were observed only after 5 days of culturing, and in cells with proportion of sodium and potassium conductances above the critical level.

Animals↗
PubMed1996

The effects of calcium channel modulators on contractions of tonic frog muscle fibres.

Effects of adrenaline (ADR) and the dihydropyridine Ca channel agonist CGP-IOS were studied on twitch and tetanic contractions of isolated tonic muscle fibres or small muscle fibre bundles containing tonic fibres of the frog Rana temporaria. Tetanization caused a gradual increase of tension between 10 and 70 Hz. CGP-IOS produced an increase in twitch amplitude. After CGP-IOS administration (2 x 10(-6) - 10(-5) mmol/l), the twitch amplitude increased and the high frequency tetanus developed more rapidly. However, during the phase of high tension level a breakdown of tetanic tension appeared and this occurred earlier at higher stimulation frequencies. After the end of tetanization the contraction curve did not return to the initial level, so that the remaining contraction (contracture) lasted 2 to 5 min. Sometimes just after replacement of CGP-IOS by Ringer, a large enhancement of tetanus amplitude was observed followed by long lasting contractures. ADR (10(-5) mmol/l) increased the tetanic tension without changing the shape of tetanus but did not affect twitch amplitude. Adrenergic modulation of tension requires extracellular Ca2+. Combined administration of ADR and CGP-IOS had an integrative effect, so that independent action of each of them can be assumed. It is to suggest that direct and indirect Ca channel modulators, DHP derivatives and ADR, have different targets. The sites responsible for adrenergic modulation of the contraction may be Ca channels not identical to DHP-sensitive channels, i.e. Ca-releasing channels in SR or the DHP-insensitive Ca channels in muscle membrane.

Animals↗
PubMed1995

Beta-adrenergic regulation of voltage-dependent calcium currents in cultured skeletal myocytes of the frog Rana temporaria.

Effects of beta-agonists isoproterenol (Isp) and adrenaline (Adr) and beta-adrenoblocker obsidan (Obs) on the voltage-dependent calcium currents in cultured embryonic skeletal myocytes were studied at various stages of development ranging from day 2 to 10, using the whole-cell patch-clamp technique at 19-21 degrees C. Adr (or Isp) in concentrations 0.1-10 mumol/l increases the amplitude of both the slow dihydropyridine(DHP)-sensitive calcium current (ICa) and the fast-activated DHP-insensitive ICa. From day 2 to 6 after myoblast plating, Adr and Isp did not change the amplitude of ICa at all or slightly increased it. Obvious strong positive effects (an approximately twofold amplitude increase) on the calcium channels have been observed in 7-10-day-old myocytes only. beta-adrenoblocker obsidan known to abolish the positive beta-agonist effect, had a positive effect on membrane calcium currents. It may have been a result of the immaturity of the beta-adrenergic regulatory system of the myocytes. It is concluded that the beta-adrenergic regulatory complex can stimulate the activity of the fast and the slow voltage-dependent calcium channels of the frog skeletal myocytes, and that there is a distinct developmental stage at which a functioning beta-adrenergic regulatory complex appears in the membrane of skeletal myocytes.

Adrenergic beta-Agonists↗
PubMed1995

Pharmacological analysis of voltage-dependent potassium currents in cultured skeletal myocytes of the frog Rana temporaria.

Previously, the existence of nine types of outward potassium current (IK) was shown. The whole family of IK may be divided into two groups: fast transient currents (f) with time to peak less than 70 ms (at test potential near 0 mV), and slow (s) components (Lukyanenko et al. 1993). The latter were completely blocked by 4-aminopyridine (4-AP) and the former were more sensitive to TEA than slow IK. In the present study we analyzed the effects of calcium blockers on different types of IK using the whole-cell patch-clamp technique. One to seven-day-old myocytes without slow calcium current and without contact with nerve cells were examined. Extracellullar application of 40-80 mumol/l dihydropyridine (DHP) antagonist nifedipine did not change maximal conductance of K-channels, but induced a parallel shift by 5-10 mV of chord conductance curve along the voltage axis in the direction of more negative potentials. Quinidine in concentrations 30-200 mumol/l caused a reversible block of the fast and the slow IK (C0.5 = 75 mumol/l), and enhanced the current decay (2-3-fold at 150 mumol/l). Verapamil (VP) in concentrations 100-700 mumol/l reduced IK with dose-dependent effect (C0.5 = 200 mumol/l) and changed its kinetic properties. VP 100 mumol/l caused a complete irreversible block of the slow IK. VP reduced the time inactivation constant of fast IK with a dose-dependent effect (8-10-fold at 300 mumol/l), and this effect was stronger during depolarizing pulses. The latter points to the possibility that the fast K-channels preferentially bind VP in open state. An analysis of the effects suggests that K-channels of the frog myocytes could be divided into 2 groups: 1) K-channels which irreversibly blocked by VP and 4-AP (slow), and 2) those reversibly inhibited by VP and 4-AP (fast potassium channels).

4-Aminopyridine↗
PubMed1994

Thermal dependence of force-velocity relation of lamprey live striated muscle fibres.

The thermal dependence of the force-velocity relation (P - V) in thin (20-40 fibres) live twitch muscle bundles from suction apparatus of lamprey by force-clamp method was investigated. The P - V relation was hyperbolic and Hill's constants were as follows: a/P0 was 0.13 +/- 0.01 and 0.08 +/- 0.01 (mean +/- S.E.M.), b was 0.46 +/- 0.02 and 0.65 +/- 0.03 at 8 degrees C and 18 degrees C, respectively. The maximal isometric tension (P0) was about 100 mN/mm2 at 8 degrees C, 18 degrees C, and 22 degrees C. After the temperature was switched from 8 degrees C to 18 degrees C, the dependence of P0 on incubation time was observed. The maximal power output determined from P - V relation using Hill's equation was 0.062 +/- 0.002 and 0.056 +/- 0.001 at 8 degrees C and 18 degrees C, respectively. The maximal velocities of shortening (V0) were 3.9 +/- 0.1 L0/s and 7.2 +/- 0.2 L0/s at 8 degrees C and 18 degrees C, respectively. Q10 for V0 in this range of temperatures was 1.86. a/P0 and power output were about 2 times lower than those reported in literature for other animals. In general, the thermal dependence of the parameters studied was similar to those reported for fish muscles and skinned lamprey muscles, P0 being relatively independent, V0 highly dependent, and a/P0 inversely dependent on temperature.

Animals↗
PubMed1994

Voltage dependent fast calcium current in cultured skeletal myocytes of the frog Rana temporaria.

Voltage dependent calcium currents in cultured frog embryonic skeletal myocytes at stages of development ranging from 2 to 9 days were studied using the whole-cell patch clamp technique at 19-21 degrees C. Membrane currents were recorded in the presence of 2 mmol/l Ca2+ (outside), and 60 mmol/l CsCl and 50 mmol/l TEACl (inside). In the absence of sodium current two components of inward current were observed in response to depolarization already during the early stages of myogenesis: the well-known slow dihydropyridine (DHP)-sensitive calcium current (ICa,s), and a fast-activated current. Both components persisted in the presence of 2 mumol/l tetrodotoxin. The fast-activated component was enhanced upon addition of 6 mmol/l Ca2+ or Ba2+ to the external recording solution and was decreased when the standard external solution was replaced by Ca2+ free solution. Thus, the fast component of the inward current was also carried by Ca2+ (ICa,f). Unlike ICa,s, it was not blocked with 30-150 mumol/l DHP nifedipine. During 7 s depolarization ICa,f was detected at approximately -50 mV, 20 mV more negative than the membrane potentials at which ICa,s appeared. At various test potentials t0.5 for activation of ICa,f was 8-20 ms, and the current declined during depolarization with tau in of 500-800 ms. These results indicate the existence of two types of voltage-dependent Ca2+ channels in early stages of development of frog myocytes, both known in mature frog skeletal muscle fibres.

4-Aminopyridine↗
PubMed1993

Voltage dependent ionic currents in frog cultured skeletal myocytes.

The voltage dependent ionic currents in cultured embryonic skeletal myocytes at stages of development ranging from 1 to 6 day were studied using the whole-cell patch clamp technique. Sodium (INa) and calcium (ICa) inward and potassium (IK) outward currents were observed at all stages. INa did not differ from that described in adult frog striated muscle fibres. Slow ICa was mediated by current through dihydropyridine sensitive Ca channels and it did not differ in its kinetics from corresponding slow ICa in frog adult twitch muscle fibres. In about 10% of cells examined for ICa, this current was significantly slower and similar to ICa described in frog tonic muscle fibres. In some cases two slow calcium currents with distinguishable kinetics were recorded in the same myocytes. Fast dihydropyridine-insensitive noninactivating ICa could also be observed. At least 6 types of IK were registered, with approximate time-to-peak (at test pulse of -10 mV) 5, 12, 20, 30, 50 ms (fast IK) and more than 7 s (slow IK). Three of them (5, 20 and 30 ms) predominated in 3-day cultures and disappeared in 6-day-old cultures. IK in myocytes did not correspond fully in the kinetics to IK reported in adult frog skeletal muscles. Channels associated with transient fast and noninactivating slow IK were shown to be highly sensitive to low temperature (+5 degrees C).

Animals↗
PubMed1992

[Efferent potential-dependent ionic currents developing in frog myoblast culture].

Variety of outward voltage-dependent currents in cultured frog myoblasts were registered by means of whole cell voltage clamp. Six types of potassium currents (Ik) which reach the peak value (-10 mV) in 5, 12, 20, 30, 50 ms (fast) and do not reach the maximum in 7 s (slow) were established. High sensitivity to low temperature (+5 degrees) was shown for channels of very fast and of slow non-inactivated Ik. The assumption is made that some of Ik--5, 20 and 30 ms to peak are especially characteristic of myoblasts fusion stage.

Animals↗