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Biomedical subjects

G Roy

Publications and source records attributed to G Roy.

At least 145 records · Page 8Linked to original sources
PubMed1976

Spin labels as probes for tetraphenylboron ion interaction with liposomes.

The effects of tetraphenylboron (TFB) on the molecular organization of lipids within phosphatidylcholine (PC) liposomes were investigated using the spin-labeled method. Perturbations at the surface of the lipid were probed using stearamide and cholestane spin labels; perturbations in the hydrophobic-portion were probed with spin-labeled amphiphilic fatty esters.

Binding Sites↗
PubMed1975

Properties of the conductance induced in lecithin bilayer membranes by alamethicin.

Current-voltage relations have been measured across lecithin bilayers doped with alamethicin molecules. The results show that there are two aspects of the induced conductances, a voltage-dependent and a voltage-independent conductance. Both have been characterized as a function of alamethicin and KCl concentration. The two aspects of the conductances do not show the same changes with those two variables. The voltage-independent conductance is affected very little by changes in KCl concentration, and its dependance on alamethicin concentration reveals that it is produced by two or three alamethicin molecules. The voltage-dependent conductance is shifted by the changes in KCl concentration only when the concentrations are greater than or equal to 100 mM; below 100 mM KCl the slope of the log conductance-voltage curve is also reduced. The effect of changing alamethicin concentration reveals that nine or ten molecules are involved for KCl concentrations larger than 100 mM; if the KCl concentration is less than 100 mM, the effect of changing the alamethicin concentration is reduced. Time-dependent measurements have also been performed; only one time constant was found and it is strongly voltage-dependent. Also a very slow voltage-dependent absorption process is found. These results can be explained if it is assumed that pores are formed of a mixture of charged and uncharged alamethicin molecules when a voltage is applied and that uncharged alamethicin can also form pores without applying a voltage, once the absorption process has been started by previously applied voltages. The voltage dependence of the time constant seems to indicate that the voltage-dependent pore formation is produced by aggregates of charged alamethicin rather than independent molecules.

Alamethicin↗
PubMed1975

Induction kinetics of delayed light emission in spinach chloroplasts.

Induction curves of the delayed light emission in spinach chloroplasts were studied by measuring the decay kinetics after each flash of light. This study differs from previous measurements of the induction curves where only the intensities at one set time after each flash of light were recorded. From the decay kinetics after each flash of light, the induction curves of the delayed light emission measured 2 ms after a flash of light were separated into two components: one component due to the last flash only and one component due to all previous flashes before the last one. On comparing the delayed light induction curves of the two components with the fluorescence induction curves in chloroplasts treated with 3-(3,4-dichlorophenyl)-1,1-dimethylurea and in chloroplasts treated with hydroxylamine and 3-(3,4-dichlorophenyl)-1,1-dimethylurea, the component due to the last flash only is found to be dependent on the concentration of open reaction centers and the component due to all previous flashes except the last is dependent on the concentration of closed reaction centers. This implies that the yield of the fast decaying component of the delayed light emission is dependent on the concentration of open reaction centers and the yield of the slow decaying component is dependent on the concentration of closed reaction centers.

Chloroplasts↗
PubMed1972

Kinetic properties of the sodium current in striated muscle fibres on the basis of the Hodgkin-Huxley theory.

1. The kinetic properties of the sodium current in skeletal muscle fibre, obtained from records in a double sucrose-gap apparatus, have been analysed in terms of the Hodgkin-Huxley formulation by means of a curve fitting computer program.2. The net sodium currents were obtained by subtracting records in Ringer and Ringer tetrodotoxin; the currents are inward for depolarizations V from +25 to +128 mV (V(Na)). The I(Na)-V characteristic shows a small inward rectification for V > + 128 mV.3. The characteristics of both sodium conductance and permeability are described.4. The activation and inactivation parameters, m and h, are calculated and compared with those experimentally established in a previous work (Ildefonse & Rougier, 1972) and with the results of Adrian, Chandler & Hodgkin (1970).5. The currents calculated with these parameter values fit rather well with the experimental ones, the permeability approach being slightly better.6. The main difference between the experimental and calculated curves is the slower inactivation of the calculated current at V = +55 mV; this difference is envisaged as a possible consequence of some activity in the tubular system of the muscle fibre.

Animals↗
PubMedDate not supplied

Serological response to tetanus toxoid: a field study in Pondicherry, India.

To study the serological response to various doses of tetanus toxoid given to pregnant women, 320 samples of blood obtained from 173 pregnant women were analysed using the indirect haemagglutination technique. Two doses of toxoid were necessary to achieve protective titres in women who were previously unimmunized. The antibody levels appeared to persist for up to 4 years. During a subsequent pregnancy, a single booster dose of toxoid was sufficient to raise the titres adequately for protection. These findings are in accordance with the immunization programme followed for prophylaxis against tetanus among pregnant women.

Antibody Formation↗
PubMedDate not supplied

Ca2+ oscillations induced by histamine H1 receptor stimulation in HeLa cells: Fura-2 and patch clamp analysis.

The response of HeLa cells to histamine H1 receptor stimulation is characterized by periodic increases in cytosolic free Ca2+ concentration. The mechanisms underlying this oscillatory behaviour are not well understood. Fura-2 and patch clamp experiments carried out on HeLa cells have previously shown: (a) that Ca2+ oscillations are not initially dependent on the presence of external Ca2+, that external Ca2+ is required to maintain the oscillatory activity; (b) that a depolarization of the cell membrane leads to an inhibition of Ca2+ oscillations during the external Ca2+ dependent phase of the process; and (c) that Ca2+ oscillations can be abolished during this latter phase by the exogenous addition of Ca2+ channel blocking agents, such as Co2+ or La3+. The contribution of the inositol phosphate pathway to Ca2+ oscillations was more recently investigated in whole cell experiments performed with patch pipettes containing IP3 or the non-hydrolysable GTP analogue GTP-gamma S. Clear periodic current fluctuations were recorded using both patch pipette solutions. Assuming that the intracellular IP3 level remained constant under these conditions, these findings provide direct evidence that the Ca2+ oscillations in HeLa cells do not arise from a periodic production of IP3. The effect of the internal and external cell pH on the oscillatory process was also investigated in Fura-2 and patch clamp experiments. It was found that an increase in intracellular pH from 7.4 to 7.7 during the external Ca2+ dependent phase of the histamine stimulation abolishes the appearance of Ca2+ spikes whereas, a cellular acidification to pH 7.2 maintains or stimulates the Ca2+ oscillatory activity. The former effect was observed in the absence of Ca2+ in the bathing medium, indicating that the inhibitory action of alkaline pH was not related to a reduced Ca2+ entry. An increase in extracellular pH from 7.3 to 9.0 in contrast elicited an intracellular Ca2+ accumulation which resulted in most cases in an inhibition of the oscillatory process. This effect was dependent on external Ca2+ and was observed in alkaline internal pH conditions (pH 7.7). These observations suggest: (a) that the net Ca2+ influx in HeLa cells is strongly dependent on the cell internal and external pH; and (b) that the magnitude of this Ca2+ influx controls to a large extent the oscillation frequency. Finally, an inhibition of the histamine induced Ca2+ oscillatory activity was observed following the addition of the Ca(2+)-induced Ca(2+)-release (CICR) inhibitor adenine to the external medium.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium↗