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B Constantin

Publications and source records attributed to B Constantin.

At least 37 records · Page 2Linked to original sources
PubMed1995

Myoblast fusion is not a prerequisite for the appearance of calcium current, calcium release, and contraction in rat skeletal muscle cells developing in culture.

During in vitro development of rat skeletal muscle cells, contraction and calcium currents progressively appear after fusion of myoblasts. To investigate whether muscle-specific functions are expressed in the absence of myoblast fusion, rat neonatal muscle cells were cultured in a differentiation medium under conditions that are well known to inhibit fusion: prolonged culture in a low-calcium medium or treatment with cytochalasin B. We have demonstrated that the fusion-arrested cells expressed differentiative properties in L-type calcium current, transient release of calcium ions from internal stores in response to caffeine and depolarizing agents, and contraction elicited by depolarization. Properties and potential-dependence of L-type calcium currents were similar to that in control fused cells, but T-type calcium currents were not observed, while both types coexist in myotubes. Properties of calcium transients and voltage dependence of contraction suggested that the excitation-contraction mechanisms were well established. However, comparing to well-developed myotubes at the same time of culture, the characteristics of calcium transients and contraction of fusion-arrested cells were closer to those of younger myotubes, which can be interpreted in terms of a delay in maturation of excitation-contraction coupling and contractile machinery. All these observations demonstrate that myoblast fusion is not necessary for triggering the establishment of calcium transport and release and contractile functions of rat muscle cells developing in culture. The appearance of muscle-specific functions is consistent with previous results demonstrating that the fusion-arrested cells express muscle-specific proteins and structures.

Acetylcholine↗
PubMed1995

Properties of calcium currents and contraction in cultured rat diaphragm muscle.

The characterization of calcium currents and contraction simultaneously measured in cultured rat diaphragm muscle cells was carried out in the present study. Whole-cell patch-clamp experiments were designed to further elucidate the mechanism of excitation-contraction (E-C) coupling in diaphragm which, though generally considered a skeletal-type muscle, has been reported to exhibit properties indicative of a cardiac-like E-C coupling mechanism. Normalized current/voltage (I/V) curves for two concentrations of external calcium (2.5 and 5 mM) were obtained from diaphragm myoballs. Both curves showed peaks corresponding to the activation of a T-type calcium current and a dihydropyridine-sensitive L-type calcium current. The normalized curve for the voltage dependence of the activation of contraction in diaphragm myoballs followed a typical Boltzmann-type relationship to the peak of contraction. Thereafter, the curve declined in a manner that was more pronounced in diaphragm compared to that measured in additional experiments using cultured rat limb muscle myoballs. This effect could be interpreted in terms of a more pronounced participation of the L-type current in E-C coupling in cultured diaphragm muscle. An increased likelihood of cultured diaphragm muscle to undergo depletion of sarcoplasmic reticular calcium stores during repetitive stimulation, or a heightened propensity for the voltage sensor for E-C coupling in diaphragm to enter the inactive state could also explain this effect. Maximal contractile activity was only slightly affected when the L-type current was blocked by externally applied cadmium (2 mM) or cobalt (3 mM), suggesting that a pronounced calcium-current-dependent component of contraction is unlikely in cultured diaphragm muscle. These results show that T- and L-type calcium channels are expressed in cultured rat diaphragm muscle cells and that, in contrast to cardiac muscle, the entry of calcium ions via L-type voltage-dependent calcium channels is not a prerequisite for contraction. Differences in the voltage sensitivity of contraction, observed at depolarized membrane potentials in cultured rat diaphragm and limb muscle cells, suggest that the voltage sensor for E-C coupling in diaphragm might more readily enter an inactivated configuration - possibly by a mechanism which is dependent on the concentration of external calcium.

Animals↗
PubMed1995

Cultured rat skeletal muscle cells treated with cytochalasin exhibit normal dystrophin expression and intracellular free calcium control.

Many studies performed to elucidate the molecular and cellular processes involved in muscular dystrophies have led to the working hypothesis of a key role for the cytoskeleton elements linking the extracellular matrix to myofibrils. It was recently suggested that cytochalasin B treatment of mouse soleus muscle promoted cell damage mediated by a cytosolic increase in free calcium concentration. Since intracellular calcium overload may be a primary event resulting from the alteration of cytoskeletal structure, this study was intended to evaluate whether or not the integrity of the F-actin microfilament network is necessary for calcium homeostasis. The developmental establishment of the normal cytoarchitecture was altered by treatment of myoblasts with the actin-disrupting agents cytochalasin B and D, and the effects were compared with those in myoblasts treated with colchicine. These drugs modified the morphogenesis in that they prevented the formation of elongated myotubes by myoblast fusion, but did not prevent the maturation of contractile myogenic cells. The subcellular organisation of actin filaments visualised by confocal fluorescence microscopy was modified by colchicine and cytochalasins, but appearance of contractile apparatus and mechanical activity were not precluded. Sarcolemmal addressing of dystrophin, the subsarcolemmal protein lacking in Duchenne muscular dystrophy, was not prevented by cytochalasin. The evaluation of the basal activity of cytosolic calcium measured with indo-1 suggested that the disruption of actin or microtubules did not prevent developing muscle cells to maintain a low basal calcium activity. We propose that the global integrity of the cytoskeleton network is not crucial for the maintenance of calcium homeostasis in muscle cells developing in vitro. These results are discussed with regard to current theories attempting to understand the functional consequences of an abnormal expression of the dystrophin-glycoprotein complex interacting with the extracellular matrix and the cytoskeleton.

Animals↗
PubMed1993

Activation of a slow outward current by the calcium released during contraction of cultured rat skeletal muscle cells.

A slow outward current, activated during depolarization, which induced contraction in whole-cell patch-clamped rat skeletal muscle cells in primary culture [10], was extensively characterized in the present study. This current, Io, was simultaneously recorded with the contraction as a slow outward current during the test pulse, and a slow outward bell-shaped tail after repolarization. Io never appeared below the threshold potential for contraction, and the tail amplitude displayed a similar evolution with peak contraction amplitude as a function of membrane potential. This feature is consistent with the fact that Io was suppressed when contraction was blocked by 5 microM nifedipine [10], and it suggests that Io was dependent on calcium released during contraction. This was confirmed by the fact that the presence of 10 mM EGTA in the patch pipette prevented the development of both contraction and Io, and that Io could be activated during caffeine-induced contractures without applying depolarizations. Io could be carried by K+ or Cs+ ions, but not by Na+. The pharmacology of Io was different from that of Ca(2+)-dependent BK and SK channels, since it was resistant to tetraethylammonium (135 mM), charybdotoxin (25 nM) and apamin (50 nM). Io was also insensitive to 4-aminopyridine (1 mM) but blocked by 5 mM Ba2+ without change to contraction. It was concluded that rat cultured myoballs exhibit a Cs+ permeation through an atypical K+ channel type, which is activated by the calcium released during contraction.

4-Aminopyridine↗
PubMed1993

Intracellular calcium transients induced by different kinds of stimulus during myogenesis of rat skeletal muscle cells studied by laser cytofluorimetry with Indo-1.

Resting intracellular calcium levels and intracellular calcium transients induced by three types of stimulus (acetylcholine, high potassium and caffeine) were recorded, during in vitro myogenesis, by means of a ratiometric fluorescence method using the calcium probe Indo-1 under laser illumination. Resting levels seemed to decrease with the age of cultured cells and the depolarization-induced transients, through 100 mM K+ or Ach application, were progressively faster and larger as the muscle cells developed. An additive mechanism, likely due to calcium entry into the cell through nicotinic acetylcholine receptors, could explain the differences observed in Ach-induced responses as compared with the 100 mM K(+)-induced ones. In myoballs (the older cells) the calcium transients exhibited progressively a biphasic shape. From data obtained in different conditions (tetrodotoxin, nifedipine, strontium and free Ca EGTA) and those indicating the appearance of caffeine-releasable intracellular calcium stores only at 2-3 days stage, and from the previously reported developmental appearance of calcium currents and contraction, it was proposed that, in young myotubes, the calcium transients were more dependent on extracellular calcium than in older cells. These developmental data are discussed in the light of a known model of the in situ biogenesis of the structures involved in excitation-contraction coupling (ECC) like transverse tubules and triads.

Acetylcholine↗
PubMed1993

Calcium current-dependent staircase in rat myotubes and myoballs developing in culture.

Calcium current and contraction were simultaneously recorded in whole-cell patch-clamped rat skeletal muscle cells grown in primary culture. Repetitive depolarizations at low frequency, which elicited calcium currents, led to a staircase response, characterized by the progressive increase of both twitch amplitude and activation rate. It was sometimes possible to elicit a staircase response in 2 or 3 day old postfusion myotubes which did not or weakly contract initially. The staircase response was dependent on calcium entry through calcium channels, since it was reversed when calcium current was depressed by means of inorganic calcium blockers or depolarization to large positive potential. The entry of calcium was also necessary to allow the development of a staircase response following caffeine-induced contractures which partly emptied the intracellular stores of calcium. These features are consistent with the idea that calcium currents allow the initial loading of intracellular calcium stores and, in later stages, serve to replenish and maintain them constant.

Animals↗
PubMed1993

Appearance and evolution of calcium currents and contraction during the early post-fusional stages of rat skeletal muscle cells developing in primary culture.

Primary cultures from enzymatically dissociated satellite cells of newborn rat skeletal muscles enabled developmental in vitro studies of mechanical and electrical properties during the first steps of myogenesis. The present work focused on the appearance, evolution and roles of two types of calcium currents (ICa,T and ICa,L) and of depolarization-induced contractile activity during the early stages of muscle cell development in primary culture. Prefusional mononucleated cells (myoblasts), young myotubes of 1 day (with less than 10 nuclei) or 2-3 days (more than 9 nuclei) and myoballs from 4-6, 7-9, 10-12 and 13-16 days cultures were patch-clamped (whole-cell configuration), and calcium currents and contraction simultaneously recorded. Sodium but not calcium currents could be recorded at the myoblast stage. In young myotubes (1 day), ICa,L was present with high incidence as compared to ICa,T, which was poorly expressed. Contractile responses appeared at the next stage (2-3 days) while the occurrence of ICa,T progressively increased. This developmental evolution of the calcium currents and contraction expression was accompanied by some changes in their characteristics: the ICa,T/ICa,L amplitudes ratio progressively increased and the time-to-peak of contraction progressively decreased with the age of myoballs. Physiological functions for calcium currents in developing muscle are suggested and discussed: ICa,T, which is transiently expressed, could be involved in the pacemaker-like activity while ICa,L could serve as an early contraction triggering mechanism and/or initially to fill and then to maintain the intracellular calcium stores.

Animals↗
PubMed1992

Progressive predominance of 'skeletal' versus 'cardiac' types of excitation-contraction coupling during in vitro skeletal myogenesis.

Simultaneous recordings, in the presence or absence of cadmium, of current and contraction of skeletal muscle cells in primary culture (myoballs) showed that the relative part of contraction depending on calcium current progressively decreases with the age of cells whereas the cadmium-insensitive component becomes predominant. The coexistence of "cardiac" and "skeletal" excitation-contraction coupling mechanisms in developing muscle and its developmental regulation are consistent with recent molecular data showing the expression, in newborn animals, of an abbreviated isoform of the alpha 1 subunit of the DHP-receptor of muscle cells.

Animals↗
PubMed1980

[Cardio-vascular therapeutics study criteria of viability of a patient with cerebral death (author's transl)].

The authors revied cardio-vascular physiologics criteria in order to valid a patient with cerebral death for a non mutilant therapeutic study conform to ethical standards as set out in the Declaration of Helsinki. Various tests are discussed. it is necessary to ensure homeostasis and to know if adrenergic receptors are active. The principal problem is the vascular effects of cerebral death on local circulations. It is concluded that it is difficult to use a patient with irreversible coma as a biological model.

Animals↗
PubMed1976

[Clinical and anatomopathologic effect of Bisolvon in respiratory resuscitation].

N cyclohexyl-N-methyl-2 amino -3.5 dibromobenzyl, amine hydrochloride or Bisolvon is an alkaloid derived from vasicine whose fluidizing effects on bronchial secretions are well-known. This study which consisted in a randomization involved 40 patients that were being submitted to a respiratory reanimation, half of whom received Bisolvon intravenously. The patients were improved by the treatment with Bisolvon as can be seen from the following: - fewer bronchial aspirations; - less fluid secretions; - a decrease in alveolar cells; - an increase in bronchial cells; - a reduced increase in total mucus. These results evidence an original action ascribable to Bisolvon on the bronchial cell.

Bromhexine↗