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Biomedical subjects

G Raymond

Publications and source records attributed to G Raymond.

At least 19 recordsLinked to original sources
PubMed1992

A third type of calcium current in cultured human skeletal muscle cells.

A third type of calcium current could be recorded on a non-negligible number of human skeletal muscle cells (normal and Duchenne dystrophic (DMD)) in primary culture. This transient current exhibited a maximum at 0 mV, a time-to-peak around 30 ms, an inactivation time constant around 70 ms and was insensitive to nifedipine. On these basis, it differentiates from T- and L-type previously described and looks like the neuronal N-type. However, this third type of current was not sensitive to omega-Cgtx, a specific N-type blocker. The occurrence and the possible role of this current are briefly discussed.

Calcium Channel Blockers↗
PubMed1992

Involvement of a pertussis toxin-sensitive G-protein in excitation-contraction coupling of intact and cut-end voltage-clamped skeletal muscle fibres.

In voltage-clamped frog muscle fibres 10 ng/ml PTX induced a decrease (approximately 35%) of tension when applied externally. Internal application in cut-end fibres significantly depressed tension after 20 min. This effect increased with time to reach 65% after 60 min. PTX shifted the voltage-dependent inactivation curve of tension by 30 mV towards hyperpolarizations and this was counteracted by raising external calcium concentration. The toxin induced a parallel decrease in tension and voltage-sensitive charge movement (49 +/- 9% and 52 +/- 6% respectively; n = 6). This was not counteracted by prior impregnation with forskolin. Internally applied GTP gamma S (500 microM) induced a simultaneous increase in tension (57 +/- 5%) and charge amount displaced (40 +/- 7%). By contrast, GDP beta S decreased tension and charge movement by 35 +/- 5% and 36 +/- 6% respectively.

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↗
PubMed1992

The L type calcium current in single hypertrophied cardiomyocytes isolated from the right ventricle of ferret heart.

OBJECTIVE: The aim was to study L type calcium current alterations in relation to the action potential lengthening induced by hypertrophy in isolated cardiomyocytes from the right ventricle of ferret. METHODS: Chronic pulmonary artery constriction was established in adult male ferrets under anaesthesia. Sham operated animals were used as controls. Four to six weeks later the heart was excised and treated with a mixed collagenase-elastase solution to isolate the right ventricular myocytes. The calcium current was investigated in control and hypertrophied cells with the whole cell configuration of the patch clamp technique. The validity of the model was tested by analysis of the structural and passive electrical characteristics of the cells, which were enzymatically isolated from right ventricles previously overloaded (4 to 6 weeks) by clipping the pulmonary artery. RESULTS: Isolated cells from right ventricles submitted to a chronic pressure overload had well preserved cellular integrity suggesting the absence of myocardial failure. This compensated form of hypertrophy was characterised by a dilated transverse tubular system, which could explain the increased membrane capacity. Such cells developed a prolonged action potential with a less pronounced fast repolarisation phase inducing a higher plateau phase. When studied in physiological Tyrode solution the density and kinetics of the L type calcium current were not apparently modified, but a significant decrease in density was unmasked when sodium and potassium currents were suppressed by external and internal substitution of sodium and potassium by tetraethyl ammonium. CONCLUSIONS: The decrease in L type calcium current cannot be involved in the lengthening of action potential observed on hypertrophied myocytes, but it could account for the depressed contractile activity. A noticeable decrease of the transient outward current is suggested to explain the action potential alterations.

Action Potentials↗
PubMed1992

Neonatal transport in Texas.

The critically ill newborn requires specialized care, which is generally provided in neonatal intensive care units (NICUs). We surveyed all identifiable NICUs in the state of Texas to study deficiencies in the current system. Despite the existence of many neonatal transport teams, little or nothing has been done to coordinate similar efforts at different programs or to organize programs into sharing the responsibility of transport among the less served areas of Texas. The lack of adequate reimbursement may be a limiting factor in the organization and regionalization of neonatal transport. We urge further efforts toward coordination and regionalization of transport with an examination of reimbursement policies to allow teams to share equally the responsibility of neonatal transport in Texas.

Catchment Area, Health↗
PubMed1991

Possible involvement of a chloride conductance in the transient outward current of whole-cell voltage-clamped ferret ventricular myocytes.

The transient outward current was studied, using the whole-cell patch-clamp technique, in isolated ventricular cells from the ferret heart. In the presence of 4-aminopyridine and cadmium chloride which respectively blocked the Ca-insensitive and the Ca-dependent outward currents, a residual transient outward current was observed in about 30% of the cells tested. This current was suppressed in external hypochloride solution, completely inhibited by SITS (3 mM) and reversed at the equilibrium potential for chloride ions. This suggests the presence of a chloride permeability which could contribute to the repolarization phase of the cardiac action potential.

Action Potentials↗
PubMed1991

The correlation between the increase in slow outward current and in contraction induced by caffeine, ryanodine, and rapid cooling in voltage-clamped frog muscle fibers.

The effects of caffeine, ryanodine, and rapid cooling were tested on the depolarization-induced contraction and the apamin-insensitive slow outward current (Iso) of voltage-clamped (double mannitol gap) single frog muscle fibers. Subthreshold caffeine concentrations (0.5-2 mM) induced a monotonic increase in contractile and Iso amplitude. Whatever the concentration, the increase in contraction was roughly twice the one in current. Similar results were obtained upon rapid cooling (20-4 degrees C) in the presence of 0.5 mM caffeine. In the absence of external Na+ (choline-substituted) 10(-5) M ryanodine induced a delayed increase (approximately 30 min) in contraction and in current, shortly before the development of a drastic and irreversible contracture. Here again, the increase in contraction was twice that in current. In the presence of 5 mM tetraethylammonium (TEA) and (or) 25 nM charybdotoxin, 2 mM caffeine still induced a strong facilitating effect on contraction but the parallel increase in current was strongly reduced. The linear relationship between the increase in current and contractile amplitude has a slope approximately 0.5 (whatever the drug used to increase contractility); it is approximately 0.1 in the presence of TEA and (or) charybdotoxin. In conclusion, provided the changes in contractile amplitude are caused by parallel changes in depolarization-induced sarcoplasmic reticulum Ca2+ release, about 50% of the apamin-insensitive Iso is controlled by internal Ca2+ release. The main part of this current corresponds to the TEA- and charybdotoxin-sensitive component of Iso.

Animals↗
PubMed1991

Muscular strength and bone density with weight training in middle-aged women.

Previous research has demonstrated positive correlations between bone mass and both physical activity and muscular strength. There is a paucity of information describing the specific type of exercise which most benefits the human skeleton. The effects of a 1 yr weight training program on 18 middle-aged women participating in an endurance dance program (E + W) compared with 17 other women in the endurance dance program only (E) and with 19 sedentary controls (C) were studied by measuring muscular strength and bone mineral density (BMD). Eighteen women in the E + W group demonstrated increases in all strength measurements, whereas the E and C groups either had smaller increases or had declined. A significant group x test interaction term, indicating that groups responded differently over time, was observed for nondominant isokinetic elbow flexion measured through the range of motion at a constant velocity of 60 degrees.s-1 (P less than 0.05), nondominant isokinetic elbow extension at 180 degrees.s-1 (P less than 0.01), and nondominant isokinetic elbow flexion at 180 degrees.s-1 (P less than 0.05). BMD did not change significantly except that a significant group x test interaction term appeared for the radius ultradistal site (P less than 0.01). BMD of the humerus and femoral Ward's triangle increased nonsignificantly in both E and E + W over the year. This weight training program increased muscular strength but did not increase measured bone mass.

Adult↗
PubMed1990

The blockade of excitation/contraction coupling by nifedipine in patch-clamped rat skeletal muscle cells in culture.

The effects of the dihydropyridine derivative, nifedipine, well known as a blocker of calcium channels, were tested on cultured rat myoballs. Membrane currents and contractions were simultaneously recorded by means of the patch-clamp technique and a photoelectric transducing method. High concentrations of nifedipine (5 microM) inhibited the contractile responses and inward calcium current (ICa) elicited by long depolarizations. In the absence of ICa (1.5 mM cadmium in the bath), nifedipine inhibited both the ICa-independent contractile component and the outward current, supposed to depend on the intracellular calcium released during contraction. At low concentrations (0.5 microM) the blocking effects of nifedipine could be strongly enhanced by shifting the membrane potential towards less negative values (-60 mV) for 50 s prior to the test pulse. A blocking effect of nifedipine, at a usually ineffective concentration (0.1 microM), could also be observed when long-lasting (3 min) prepulses to 0 mV were applied from a reference membrane potential of -60 mV. This effect could be relieved by long-lasting cell hyperpolarizations (-90 mV). The blocking effects of nifedipine unrelated to ICa could be interpreted as an action on a molecule (voltage sensor) in the T-tubule membrane involved in the excitation/contraction coupling process and as a preferential binding of the dihydropyridine derivative on the inactivated form of this molecule, favored by the weak negative potentials or long-lasting depolarizations. The results provide data in favor of the existence of strong similarities between the calcium channels and voltage sensors since their operation was inhibited in a voltage-dependent manner by nifedipine.

Animals↗
PubMed1990

The depressing effect of tetracaine and ryanodine on the slow outward current correlated with that of contraction in voltage-clamped frog muscle fibres.

The effects of tetracaine (10-50 microM) and ryanodine (0.1-10 microM) were tested on the slow outward K+ current (Iso) and the mechanical tension of isolated frog muscle fibres in a voltage-clamp device (double mannitol-gap) connected to a mechanoelectric transducer. In the concentration range tested, both drugs induced a simultaneous inhibition of tension and current. In all cases the effect on tension was twice that on current. The tetracaine-induced current and tension blocks were fully reversible and dose-dependent. In contrast the ryanodine effects on current and tension were not reversible and did not exhibit a dose dependence except for the delay before the onset of the response, which was shortened when the concentration was raised. Linear regression analysis of the time-dependent and dose-dependent effects of both drugs indicated a strong correlation between the decreases in tension and current. It is concluded that the slow outward current is partly under the control of the Ca2+ release from sarcoplasmic reticulum during contraction.

Alkaloids↗
PubMed1990

Phenytoin preferentially inhibits L-type calcium currents in whole-cell patch-clamped cardiac and skeletal muscle cells.

The effect of the anticonvulsant diphenylhydantoin (phenytoin) was tested on the inward calcium currents of whole-cell patch-clamped cells from rat and human muscles and from frog atrium. A concentration of 10 microM phenytoin was required to obtain a threshold inhibitory effect and, even with high concentrations (100 microM), the inhibition was not complete. In skeletal muscle (rat and human cells in culture), phenytoin (30 microM) exerted a more potent effect on the high-threshold calcium current (ICa,L inhibition: 53 +/- 6% mean +/- SDn-1) rather than on the low-threshold one (ICa,T inhibition: 16 +/- 10%). Similar results were obtained on dissociated frog atrial cells. These data are to be contrasted with those previously reported on neuronal cells, where specific inhibition of ICa,T was reported. Thus, the action of phenytoin appears to be different in muscle and nerve so that phenytoin does not appear to be a specific inhibitor of ICa,T.

Animals↗
PubMed1990

Calcium currents in normal and dystrophic human skeletal muscle cells in culture.

Human muscle cells obtained from biopsy specimens were grown in a primary culture system and electrophysiologically studied. Whole cell patch-clamp recordings revealed the presence of two types of calcium currents: (i) a low-threshold (-60 mV) one (ICa, T) with fast activation and inactivation kinetics (time-to-peak: 39 ms at -30 mV); and (ii) a high-threshold (-10 mV) one (ICa,L) with slower kinetics (time-to-peak: 550 ms at 20 mV). These two types of calcium currents could be also distinguished by their pharmacological characteristics since ICa,L was sensitive to the antagonist and agonist dihydropyridine derivatives contrary to ICa,T which was completely resistant to these compounds. These functional calcium channels existed both in normal and Duchenne dystrophic (DMD) human skeletal muscle cells in culture. We discuss a possible role of these two types of calcium channels in the myoplasmic calcium accumulation observed in the Duchenne muscular dystrophy.

Calcium↗
PubMed1990

An efficient isolation procedure of Ca-tolerant ventricular myocytes from ferret heart for applications in electrophysiological studies.

A simple procedure which provides a large yield of isolated ferret ventricular myocytes is described. The enzymatic dissociation was performed by perfusion of the whole heart with the "Langendorff method" at 37 degrees C, without an incubation period. Special attention was given to the period of perfusion with Ca-free or low-calcium containing solutions and to the proportion of both collagenase and elastase used. The viability and calcium tolerance of the isolated cells were tested by ultrastructural and electrophysiological studies. Photo-microscopy showed that 60 to 80% of the isolated cells had an elongated shape (18 microns in diameter, 150 microns in length) and did not beat spontaneously in normal Tyrode solution. The morphological and ultrastructural integrity of these cells was shown in SEM by their smooth surface with regularly spaced T-tubule openings and in TEM by the regular distribution of the transverse tubular system, mitochondrium and sarcomeres. Using the whole-cell patch-clamp technique, they had a resting membrane potential of -72 mV, two types ("Purkinje like" and "ventricular like") of action potentials could be elicited and they were correctly affected by well-known modulators of calcium channels. This technique was successfully applied to the rat heart and could be used for heart dissociation of small mammals. It can simultaneously provide isolated cells of different regions of the heart and can be easily and routinely used by any investigator.

Action Potentials↗
PubMed1990

Propranolol metabolism by isolated hepatocytes from normal and cirrhotic rat livers: the effect of albumin.

Several recent reports have shown that the hepatic uptake and subsequent elimination of some substrates is faster in the presence of albumin than in its absence, as if some of the substrate bound to albumin was also available for uptake. In the present study, we examined the effect of albumin on the clearance of propranolol by isolated rat hepatocyte suspensions. The clearance of total drug decreased progressively as albumin concentration increased. There was also a progressive decrease in the free fraction of propranolol and the net result was an increase in the clearance of unbound drug (+50% at 40 g/L albumin). This increase was not due to an oncotic pressure effect of albumin, nor to the presence of fatty acids bound to albumin. The clearance of propranolol by isolated hepatocytes from cirrhotic rats was decreased compared with controls (-50%), and albumin also increased propranolol free clearance, albeit to a lesser extent than in control animals. Our results indicate that albumin facilitates the elimination of propranolol by hepatocytes, possibly because of surface-mediated catalysis of the albumin-propranolol complexes.

Albumins↗