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R Motais

Publications and source records attributed to R Motais.

64 records · Page 4Linked to original sources
PubMed1975

Transmembrane exchange of chloride with bicarbonate ion in mammalian red blood cells: evidence for a sulphonamide-sensitive "carrier".

1. It is well known that red blood cells suspended in isotonic NH4Cl solution swell because penetration of NH3 induces a transmembrane exchange between Cl-o and OH-i(or HCO3-i). The rate of swelling thus depends on the speed of the transmembrane exchanges and on the amount of anions available for exchange. 2. It has been demonstrated in experiments carried out in a CO2-free medium that OH-ions are poorly permeating whereas the permeability for HCO3-is very high. Thus the rate of swelling is largely dependent on the intracellular HCO3-concentration. In this context the well-known inhibitory effect of sulphonamides upon swelling can be interpreted, and always has been until now, as being due to the inhibitory action of the drug on the intracellular carbonic anhydrase. However, this inhibitory effect could also result from a direct action of the drug on the transmembrane exchange; it would explain why under conditions of total carbonic anhydrase inhibition we have shown that the inhibition of swelling is far from maximal. 3. A direct experimental evidence of such an effect of carbonic anhydrase inhibitors on the transmembrane exchange of Cl-with HCO3- was obtained with benzolamide (Cl 11,366), Cl 13,580 and ethoxzolamide. Surprisingly enough, however, acetazolamide (Diamox) does not affect the transmembrane exchange process. 4. The inhibitory effect of sulphonamides on HCO3-transport process is discussed in terms of an interaction of the drug with a transport system common to HCO3- and organic anions.

Acetazolamide↗
PubMed1973

Sodium movements in high-sodium beef red cells: properties of a ouabain-insensitive exchange diffusion.

1. The relative importance of the Na efflux components in beef red cells has been evaluated. The component which is insensitive to ouabain, which does not require external K but depends on the presence of external Na, accounts for about 90% of the total Na efflux.2. The experiments reported in this paper are consistent with the presence of an ouabain-insensitive Na(+)-Na(+) exchange process accounting for this ouabain-insensitive external Na dependent efflux.3. A strictly parallel behaviour of influx and efflux is observed when the pH is altered. The exchange diffusion process is inhibited over 90% by a decrease in pH from range pH 8.0-5.5.4. Both Na efflux and influx are markedly increased by raising the temperature from 27 to 37 degrees C.5. Energy depleted cells and fresh cells behave similarly in respect to Na movements. In depleted resealed ghosts, a large Na-dependent efflux occurs. No chemical energy and no special nucleotide is required for the Na(+)-Na(+) exchanges.6. When the external or internal Na concentrations are changed, a parallel behaviour of influx and efflux is observed.7. The relation between the magnitude of the exchange diffusion flux and the external or internal Na concentration fits quite well the Michaelis-Menten equation suggesting that only one Na(+) reacts with the transport mechanism. The affinity for Na is lower however at the outer surface than at the inner border of the membrane.8. The relation between this exchange process, the ouabain-insensitive Na-Na exchanges found in human red cell, and Ussing's model of exchange diffusion is discussed.

Animals↗
PubMed1973

Characteristics of a sulphydryl group essential for sodium exchange diffusion in beef erythrocytes.

1. In the beef red blood cell, the component of the Na efflux which is insensitive to ouabain but depends on the presence of external Na, is not affected by furosemide but is reduced by several agents: ethacrynic acid, dinitrofluorobenzene, p-chloromercuribenzene (PCMB), N-ethylmaleimide and p-chloromercuribenzene sulphonate (PCMBS). Some of these agents increased a parallel passive permeability which could mask the reduction of efflux.2. N-ethylmaleimide and PCMBS, which in our experimental conditions (initial concentration 5 x 10(-4)M and 5 x 10(-6)M respectively, haematocrit 7.7%) do not increase the leak, inhibit Na influx and efflux markedly and equally. This provides further evidence of the existence of a typical ouabain-insensitive Na exchange diffusion in beef red blood cell.3. Inhibition of the exchange diffusion mechanism by N-ethylmaleimide or PCMBS is not total and their inhibitory effects are slightly additive. Various arguments suggest that their effects on exchange diffusion can be attributed to a reaction with sulphydryl groups.4. These sulphydryl groups are rapidly titrable by a poorly penetrating agent such as PCMBS, and the inhibitory effect is rapidly reversible. Thus, it is assumed that the sulphydryl groups containing proteins are superficially located on the outer border of the membrane.5. After inhibition, there is no change in half saturation constant for the complexing reaction for transfer, suggesting that the inhibited sites are no longer functioning but that the uninhibited sites are in every way normal.6. N-ethylmaleimide and PCMBS act similarly in sheep red blood cells.7. PCMBS does not affect sodium movement in human erythrocytes, but N-ethylmaleimide inhibits markedly the ouabain-insensitive Na efflux.

Animals↗
PubMed1966

Exchange diffusion effect and euryhalinity in teleosts.

The sea water (SW)-adapted euryhaline Platichthys flesus, and the marine Serranus exchange about 50% of their internal sodium with the external sodium per hour. This rate of exchange decreases with decreasing salinity of the adaptation medium. When the flounder is transferred from SW to FW an instantaneous 90% reduction of the Na and Cl outflux is observed. About 30 min later a second, progressive, reduction occurs. The outflux reductions appear to result from two types of regulatory mechanisms reducing gill permeability and preventing excessive salt loss. The first reduction corresponds to independent "Na- and Cl-free effects" as shown by transfers to artificial media containing either Na or Cl with an impermeant co-ion. The pattern of simultaneous rapid variations of Na influx and outflux for a range of salinity changes in flounder adapted to SW, 1/2 SW, or 1/4 SW has been studied. The data are compatible with the hypothesis of an exchange diffusion mechanism characterized by a coupling of both unidirectional fluxes. The affinity of the exchange diffusion carrier for sodium has been measured (Km approximately equal to 400 mM). The delayed reduction would result from a progressive diminution of the quantity of carrier available but without modification of its affinity for sodium. When the stenohaline marine perch is transferred from SW to FW, a 40% reduction of the outflux is observed. But it is not the result of an exchange diffusion effect as it is related to the external osmolarity change and not to the NaCl concentration change. Furthermore no delayed reduction is observed after transfer into FW. This transfer is accompanied by a heavy loss of electrolytes resulting in a rapid decline of the plasma electrolyte level and death. A comparative survey of the relative importance of these regulatory mechanisms has been made.

Adaptation, Physiological↗