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Biomedical subjects

G Leblanc

Publications and source records attributed to G Leblanc.

At least 109 records · Page 6Linked to original sources
PubMed1976

Intracranial dysgerminomas.

We have reported three cases of intracranial dysgerminoma. The origin of these tumors has been controversial for a long time. It is now accepted that they develop from germ cells. The diagnosis is often difficult to confirm because of the varity of signs. If their origin is now accepted, the best way to deal with these lesions is still controversial. They can be macroscopically removed if they are in the pineal region. Such treatment is not possible for suprasellar tumors. Since these tumors can metastasize, radiation should be administered as soon as a pathological diagnosis is obtained. It is our belief that it should be administered to the whole spinal axis.

Adolescent↗
PubMed1975

Transient current changes and Na compartimentalization in frog skin epithelium.

Experimental conditions are described in which transient and positive current responses across isolated frog skin epithelia can be elicited by sudden addition of Na and Li ions (2--40 mM) in the outer bathing solutions. Subsequent return to outer Na (or Li) free conditions produce similar transient current changes but in the opposite direction. Analysis of the curve responses shows that the transient component of each curve is best described by a single, fast exponential term equation in case of Na addition to preparation unpoisonned with ouabain. In contrast, an equation including two exponential terms (a fast and a slow one) is required to fit the curve responses observed across ouabain treated epithelia or if Li is added outside. The transient responses were not significantly altered by substituying Cl for SO4(2)-anions. They were completely prevented by Amiloride (5-10(-5) M), increased by oxytocin (20 mU/ml) and markedly dependent upon the outer Na concentration. Interpreted in term of compartmental analysis, these observations suggest that a) the frog skin epithelium contains 2 separated but communicating compartments having different degrees of accessibility from outside; b) only that compartment filling at a fast rate (0.5 min) is involved in the transepithelial Na transport; c) the other one, filling at a rate of 4 to 7 min, is resplenished only under conditions where the basal pump system has a reduced activity. Tentative localization of these compartment is proposed.

Amiloride↗
PubMed1975

Na and K movements across the membranes of frog skin epithelia associated with transient current changes.

The ionic composition of the current crossing each membrane of the frog skin epithelia during a) the positive and transient current responses elicited by sudden addition of Na ions to the outer Na free medium b) the negative and transient current responses observed when Na loaded preparations are suddenly exposed to outer Na free solution was determined using isotopic techniques. It is shown that Na ions carry the current across the outer membrane while K ions are mainly involved in the transfert of charges across the inner membrane. The amount of Na accumulated by the epithelial cells during the responses is correlated to the area under the transient part of the current responses. Determinations of 24Na uptake at different time of these transient positive responses show that the unidirectional Na influx across the outer membrane decreases as a function of time. It is suggested that the intracellular Na concentration might control the Na uptake mechanism across the outer membrane. During the negative responses, the Na efflux into the outer medium is highly correlated, either in time course or magnitude, to the current response. Both Na efflux and negative current are sensitive to amiloride, suggesting that the mechanism of Na uptake by the frog skin also is able to promote Na movement out of the epithelial cells.

Amiloride↗
PubMed1971

The effects of ethacrynic acid and other sulphydryl reagents on sodium fluxes in frog muscle.

1. Ethacrynic acid (2 mM) increased the sodium efflux from freshly dissected frog sartorius muscles. This increase was not observed in muscles previously treated with strophanthidin.2. In strophanthidin-treated muscles, the addition of ethacrynic acid (2 mM) caused a reduction of sodium efflux. The value of efflux reached in these muscles is similar to that observed in muscles immersed in sodium-free solutions containing strophanthidin.3. Ethacrynic acid reduced sodium influx into strophanthidin-treated muscles. Potassium influx was not affected by this substance. These findings suggest that the inhibitor blocks an exchange of sodium for sodium.4. The increase in sodium efflux caused by ethacrynic acid did not result from depolarization nor from an increase in [Na](i).5. Ethacrynic acid caused only a reduction of sodium efflux in muscles previously loaded with sodium by prolonged immersion in potassium-free solutions at low temperatures.6. A derivative of ethacrynic acid that lacks the ability to combine with sulphydryl (SH) groups did not reduce sodium efflux from muscles treated with strophanthidin.7. Para-chloromercuribenzoic acid (PCMB) reduced sodium efflux from control and strophanthidin-treated muscles. This reduction seems to be restricted to the sodium dependent component of the efflux.8. The inhibition of the sodium-dependent component of sodium efflux caused by ethacrynic acid and PCMB appears to have a similar mechanism, namely, the combination with SH groups.

Animals↗
PubMedDate not supplied

Recent developments in the study of potassium transport in Mycoplasma mycoides subspecies capri.

The effects of modifications in the cholesterol and fatty acid contents of membranes on the transport of potassium have been studied in Mycoplasma mycoides subspecies capri. A decrease in the cholesterol content from 110 micrograms/mg of membrane protein to less than 10 micrograms/mg of membrane protein is associated with a decrease in the level of intracellular potassium from 40 micrograms of K/mg of protein to 23 micrograms of K/mg of cell protein. Replacement of oleate plus palmitate by elaidate alone in the growth medium has only limited effects on the intracellular K content. In metabolizing cells, 42K influxes were 0.42, 0.65, and 0.69 micrograms of K/mg of cell protein per min for cholesterol-rich cells supplemented with elaidate or with oleate plus palmitate and for cells adapted to low cholesterol and supplemented with elaidate, respectively. This increase in influx was associated with an increase in membrane fluidity as determined by fluorescence polarization experiments in which 1,6-diphenyl-1,3,5-hexatriene was used as a probe. For elaidate-supplemented cells, examination of the temperature dependence of 43K influx revealed the existence of a break or a discontinuity at temperatures corresponding to modifications in the physical state of the membrane. The lack of correspondence between the patterns of K+ influx and the Mg++-adenosine triphosphatase (ATPase) activity indicates that the sensitivity of this influx to the physical state of the membrane is not attributable to the Mg++-ATPase but likely reflects an effect of membrane lipids on the K+ carrier itself.

Adenosine Triphosphatases↗