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H Godart

Publications and source records attributed to H Godart.

5 recordsLinked to original sources
PubMed1999

Regulatory volume response of erythrocytes exposed to a gradual and slow decrease in medium osmolality.

A sudden decrease in external medium osmolality (90 mosmol/kg) causes an immediate swelling of trout erythrocytes, followed by a regulatory volume decrease (RVD) due to activation of both a KCl cotransporter and a taurine transport pathway. Here, we determined how trout red cells respond when they are exposed to a gradual and slow decrease in medium osmolality (80 mosmol/kg at a rate of 0.7 mosmol/kg per min). Erythrocytes were unable to regulate their volume efficiently when swollen gradually and it increased continuously throughout the experimental period (120 min). As long as volume was increased slowly by 15-25%, regulatory pathways remained essentially inactivated, erythrocytes losing no significant amount of intracellular osmotically active solutes. Above this swelling threshold, a response was triggered but the quantity of solutes lost via the regulatory pathways was still not sufficient to counterbalance the continuous entry of water due to the slow and gradual decrease in medium tonicity.

Animals↗
PubMed1997

Do HbSS erythrocytes lose KCl in physiological conditions?

KCl cotransporter activity in sickle (HbSS) red blood cells (RBCs) was measured in cells suspended in 'simple' physiological saline, saline augmented with inorganic salts, and autologous plasma. Our results showed that the transporter was only functioning at 20% of the level of cells in saline when cells were resuspended in autologous plasma. Kinetic analysis of the data showed that plasma decreased both Vmax and Km for K+ of the transporter. The plasma factor(s) responsible was heat-stable and dialysable (i.e. size < 10 kD). Adding magnesium, calcium, inorganic phosphate or bicarbonate to 'simple' saline to mimic the effect of plasma revealed that Mg2+ and Ca2+ had no significant effect at physiological concentrations. Pi was not effective at 1.1 mM, but did inhibit significantly (42+/-2%) at 5.6 mM. HCO3- had a major inhibitory effect on K+ influx when added to saline, and was identified as the principal candidate for the plasma effect. We suggest bicarbonate may play a significant role in modifying KCl cotransport, and hence HbSS cell volume in vivo. It acts by altering the set point of the transporter via the signalling systems involved in its regulation.

Adolescent↗
PubMed1996

KCl cotransport activation in human erythrocytes by high hydrostatic pressure.

1. Pressure induced a 4- to 5-fold stimulation of the residual (i.e. oubain-bumetanide insensitive) 86Rb+ influx across the human red cell membrane. This enhancement showed a broad pHo dependence with a maximum stimulation around pHo 7. 2. At atmospheric pressure, the protein kinase inhibitors staurosporine and chelerythrine stimulated a normally silent component of 86Rb+ influx in a dose-dependent manner with a half-maximum stimulatory concentration at about 550 nM and 140 microM, respectively. The component stimulated by staurosporine was entirely Cl- dependent, but part of the chelerythrine effect was Cl- independent. 3. Staurosporine (3 microM), chelerythrine (200 microM) and N-ethylmaleimide (1 mM) stimulated further the increased residual 86Rb+ influx in cells at high pressure. 4. The serine/threonine protein phosphatase inhibitors okadaic acid, cantharidin and calyculin A inhibited the stimulatory pressure effect in a dose-dependent manner with half-maximum inhibitory concentrations of 70 nM, 2.5 microM and 3.3 nM, respectively. In contrast, deltamethrin, a specific protein phosphatase type 2B inhibitor, did not affect the stimulation by pressure, up to a concentration of 10 microM. 5. Decreasing the internal ionized magnesium concentration ([Mg2+]i) with A23187 and EDTA stimulated the increased residual 86Rb+ influx in cells at high pressure. On the other hand, increasing the [Mg2+]i nearly abolished the stimulatory pressure effect. 6. Decreasing the [Mg2+]i produced a marked change in the pHo dependence curve, with a linear increase of the 86Rb+ influx at higher pHo values. 7. We demonstrate that high pressure stimulates the normally silent component of 86Rb+ influx by modifying the phosphorylation/dephosphorylation ratio of the KCl cotransporter.

Cell Membrane↗
PubMed1994

Modulation of K(+)-Cl- cotransport in equine red blood cells.

Potassium transport was measured in equine red blood cells, using 86Rb+ influx as a convenient assay. A significant component of volume- and pH-sensitive K(+)-Cl- cotransport to the overall K+ flux was observed in all blood samples studied, although fluxes were variable between animals, and within individuals when measured at intervals over a period of weeks. The aryloxyacetic acid [(dihydroindenyl)oxy]alkanoic acid (DIOA), at a final concentration of 100 microM, inhibited most (> 95%) of the Cl(-)-dependent K+ flux, and DIOA sensitivity was therefore used to define the activity of the K(+)-Cl- cotransport. K(+)-Cl- cotransport was also sensitive to protein phosphatase inhibition with calyculin A or okadaic acid, with inhibition constants of 9 +/- 1 nM for calyculin and about 100 nM for okadaic acid. Peak fluxes were observed at an external pH of 6.7-7.0, with inhibition at higher and lower values. Volume-sensitive K+ fluxes assayed in autologous plasma, controlled for osmolaity, pH and potassium concentration, were significantly lower (28 +/- 8% of control values, n = 6) than those measured in saline. This inhibition was mimicked by the culture medium RPMI, but disappeared following dialysis of the plasma. Phosphate (5.6 mM) inhibited volume-sensitive K+ fluxes by 48 +/- 2%, n = 3; no significant effect was observed by increasing external magnesium concentrations to 0.5 or 2 mM. Thus, inhibition by RPMI, but not that by plasma, may be due to phosphate. Finally, volume- and pH-sensitive K+ fluxes were sensitive to oxygen tension and were abolished reversibly by equilibrating solutions with nitrogen, as opposed to air. Use of solutions equilibrated with different values of Po2 may account for some of the variability in equine red blood cell KCl fluxes. The importance of these observations to equine red blood cell homeostasis and haemodynamics is discussed.

Animals↗