Jean-Jacques Hajjar

Mechanism of cholesterol absorption by the hydatid cysts of Echinococcus granulosus (Cestoda)

Abstract 1. 1. The mechanism of cholesterol absorption by hydatid cysts of Echinococcus granulosus was studied in function of time of incubation, size of cysts, temperature of incubation, concentration of cholesterol substrate and presence of metabolic inhibitor. 2. 2. The results indicated that the uptake of cholesterol continuously increased with time of incubation, that small cysts absorbed cholesterol better than large ones, that the optimum temperature for uptake was 25°C and that uptake increased with increase in concentration of substrate. 3. 3. The addition of the metabolic inhibitor 2, 4-dinitrophenol did not affect the process of absorption thus eliminating the participation of the mechanisms of active transport or facilitated diffusion. 4. 4. It was suggested that mechanisms of simple diffusion and possibly exchange diffusion are operating in cholesterol absorption by hydatid cysts.

Determination of extracellular space in small intestine

Abstract 1. 1. The intestinal extracellular space differs with the different probing solutes that are utilized in its determination. 2. 2. Inulin seems to be the most suitable probing molecule utilized since its equilibrium uptake value remains constant with prolonged incubations. It distributes however in a smaller space than that occupied by mannitol or sorbitol. 3. 3. Inulin also differentiates the mucosal and submucosal spaces unlike mannitol or sorbitol. 4. 4. The extracellular space decreases with swelling and increases with shrinkage of the intestinal epithelium, the mucosal space being the compartment altered by these cell vol changes. 5. 5. A method for estimating the extracellular space in in vitro experiments is proposed.

Effect on Mn2+ on permeability properties of frog skin

SummaryMn2+ added to the inner bathing solution of frog skin caused a transient increase in potential difference (PD) and a decrease in total skin conductance and mannitol influx. Net Na flux and short-circuit current (Is. c.) were also reduced, the isotopic net flux being reduced more than Is. c. This observed discrepancy appears to be the result of Cl− retention in the outer medium since it was not observed when the skin was bathed in a sulfate-substituted chloridefree solution. The effect of Mn2+ on the inner side of the frog skin appears to be due to a reduced permeation of Na+ and Cl− through the outer barrier of the skin.Addition of Mn2+ to the outer solution bathing the frog skin caused an increase in PD and a smaller increase in Is. c. These changes were not associated with alterations in the fluxes of Na+ or mannitol and were observed only when chloride was present in the bathing solutions. The effect of Mn2+ on this side of the frog skin may therefore be due to a net retention of Cl− in the outer solution.

Ion transport in proximal and distal halves of turtle colon

Abstract 1. 1. The transmural electrical potential difference and short-circuit current measured in vitro were higher in the proximal half of the turtle colon than the distal half. 2. 2. Unidirectional fluxes of sodium measured in vitro were not different between the two halves of the colon. 3. 3. Net fluxes of Na, K, HCO3 and Cl measured by perfusion of isotonic saline into the two colons in vivo showed a higher rate of HCO3 secretion in the distal than proximal colon. Na and Cl absorption and K secretion rates were not significantly different.

The effect of vitamin B6 on alanine transport in turtle intestine

Abstract 1. 1. Pyridoxine and pyridoxal caused a decreased mucosal-to-serosal and increased serosal-to-mucosal alanine flux across the isolated intestine of the fresh-water turtle. 2. 2. The intestinal cell alanine accumulation is reduced by pyridoxine, and cell Na and K concentrations in the presence of pyridoxine were not different from those of controls. 3. 3. Alanine influx from the mucosal solution into the cell across the brushborder membrane was not influenced by vitamin B 6 . 4. 4. The findings suggest that pyridoxine and pyridoxal act mainly on the efflux processes of alanine across the cell barriers. The efflux across the mucosal barrier is increased and the efflux across the serosal barrier is decreased.

Lysine transport in turtle ventricle-I. Effect of ouabain and extracellular ions on lysine accumulation

Abstract 1. 1. Strips of turtle ventricle accumulate L -lysine to concentrations that exceed those of their bathing media by 1·5-2·0 times. 2. 2. This accumulative process is dependent on the Ca and K concentrations of the bathing medium but is not influenced by substituting choline or lithium for sodium. 3. 3. Ouabain in 10−4 M concentration inhibits lysine accumulation.This inhibition is also influenced by the electrolyte composition of the medium. It increases when calcium is raised from 1·3 to 5 mM, and decreases when 52·1 mM K is used instead of 2·1. 4. 4. A time relationship exists between the intracellular electrolyte shifts and the ouabain inhibition of amino acid uptake.

Alanine flux across rabbit peyer's patches

Abstract 1. 1. Transmural fluxes of l -alanine, l -lysine and d -galactose across rabbit Peyers patches were smaller than those across regular intestine. 2. 2. Cell accumulation of l -alanine in Peyers patches was comparable to that in intestinal mucosal cells and was partially dependent on Na concentration in the bathing medium. 3. 3. Unidirectional influx and efflux across the mucosal epithelial layer overlying the Peyers patches were not different than those across regular mucosal brush border.

Alanine influx across serosal border of Testudo graeca intestine

The influx of alanine across the serosal membrane of Testudo graeca intestinal cells with preserved epithelial orientation was examined. Our results suggest that: 1. The mechanism of alanine influx across the serosal membrane of turtle intesintal cells is a carrier-mediated process that has the characteristics of facilitated diffusion. 2. Alanine influx mechanism is independent of intra- and extra-cellular changes in Na+ and K+ concentrations, and is not altered by reversal of Na+ and K+ gradients across the serosal membrane. 3. In Na+-free media the mechanism of transport of alanine at the mucosal membrane has the same pattern of competitive inhibition by amino acids as the serosal.

Lysine transport in turtle ventricle—II. Effect of extracellular ions and ouabain on lysine fluxes

Abstract 1. 1. Unidirectional influx measurements of L -lysine into turtle ventricle strips revealed evidence of the occurrence of two Na-independent transport processes, one subject to saturation at low concentrations, and one not saturable by increasing, higher elevations of medium lysine. 2. 2. Ouabain at 10 −4 M concentration did not affect either of the influx processes, but enhanced the efflux of lysine from the cell to the medium. 3. 3. Ornithine competitively inhibited lysine influx into the myocardial strips, but arginine was not effective. 4. 4. Analysis of the data leads to the conclusion that the ouabain induced lysine extrusion from heart cells is possibly related to K extrusion.

A proposed test for the pore hypothesis

Abstract A theoretical analysis is presented for the calculation of tritiated water (3HHO) permeability coefficient in red blood cells during osmotic water flow. This method can also be used to calculate the permeability coefficients of small hydrophilic solutes under similar experimental conditions. With the aid of this analysis it becomes feasible experimentally to test the pore model hypothesis for the red blood cell membrane. Previously determined experimental values were substituted for parameters in the final equation to show how this hypothesis can be tested.