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At least 325 records · Page 18Linked to original sources
PubMed1993

Counterflow in isotachophoresis: computer simulation and experimental studies.

A computer model has been developed to predict the effects of co- and counter-current flows on electrophoretic transport. Model predictions are compared with experimental data obtained with the large-scale recycling isotachophoresis apparatus, recently developed in our laboratory. There were no significant changes in the steady state properties or the transient development of the Kohlrausch-adjusted profiles with and without flow. The application of counterflow in free flow isotachophoresis in early stages, before a steady state is achieved, can result in selective wash-out of slower sample components. Thus, the magnitude of counterflow can be used as a variable in optimizing separations. The characteristic features of the model render it also suitable for the simulation of electroosmotic flow in capillary electrophoresis in open tubes, where plug-type flow prevails.

Anions↗
PubMed1987

Implementation of a semiclosed large scale counterflow centrifugal elutriation system.

A semiclosed counterflow centrifugal elutriation system that minimizes the risks of contamination and cell loss is presented. A detailed description of the configuration of the system and its sterilization and assembly is provided along with examples of its application to large-scale separation of leukapheresis buffy coat and cadaveric bone marrow. We are currently using this system to deplete lymphocytes from human bone marrow prior to use in allogeneic bone marrow transplantation. The implementation of a semiclosed system increases the safety, ease of operation, and reproducibility of a technique that has the potential for a wide range of clinical applications.

Cell Separation↗
PubMed1993

O2 gradients and countercurrent exchange in the cat vitreous humor near retinal arterioles and venules.

Recessed cathode O2 microelectrodes were used to measure spatially detailed oxygen tension (PO2) gradients in the vitreous humor near the cat retina. Measurement sites (n = 41 in 8 cats) included single arterioles and venules and parallel vessel pairs. Mean vitreous PO2 was 37.9 +/- 1.5 (SE) Torr. Close to the retinal surface (approximately 200 microns), PO2 was found to be both higher and lower than the vitreous PO2, depending on the proximity of the microelectrode tip to retinal vessels. Both positive (inward) and negative (outward) O2 fluxes (JO2) were measured, consistent with the anatomy and expected boundary conditions in the eye. The PO2 at the closest approach above arterioles was 55.2 +/- 2.3 Torr, significantly higher than in the vitreous (P < 0.0001). All arterioles had outward JO2 with an overall mean of -2.58.10(-6) ml O2/sec/cm2. Some of the venules were also losing O2, but at much lower rates than arterioles. Several venules were gaining O2. Countercurrent transport (A-V shunting) was also seen between vessel pairs. Our experimental results allow theoretical predictions to be made for the axial drop in blood PO2 along an arteriole as a function of blood flow.

Animals↗
PubMed1995

Enzyme-enzyme interaction in the chloroplast: glyceraldehyde-3-phosphate dehydrogenase, triose phosphate isomerase and aldolase.

Apparent physical interaction between pea chloroplast (Pisum sativum L.) glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.13) and aldolase (EC 4.1.2.13) is seen in phase-partitioning, fluorescent-anisotropy and isoelectric-focusing experiments. Similarly, results obtained in phase-partitioning and isoelectric-focusing experiments indicate physical interaction between aldolase and triose-phosphate isomerase (EC 5.3.1.1). Kinetic experiments suggest that both aldolase-bound glyceraldehyde-3-phosphate can act as substrate for glyceraldehyde-3-phosphate dehydrogenase. These results are consistent with the notion that there is interaction between these three enzymes both during photosynthetic CO2 fixation and during glycolysis in the chloroplast.

Amino Acid Sequence↗
PubMed1985

The role of the cell cycle in differentiation of the cellular slime mould Dictyostelium discoideum.

During development and differentiation of the cellular slime mould Dictyostelium discoideum there appears to be a relationship between the cell cycle and cell fate: amoebae halted in G2 phase during early development differentiate into spores whereas stalk cells are formed from amoebae halted in G1 phase. It is proposed that this is because a major effect of the cell cycle is to generate heterogeneity in the cell surface properties of the developing amoebae.

Cell Cycle↗
PubMed1979

The effects of pressure on the water permeability of the descending limb of Henle's loops of rabbits.

Descending limbs of Henle's loops from rabbits were perfused in vitro. Using techniques where the collecting pipets permitted cannulation of the tubule, we were able to maintain reasonable flow rates at lower perfusion reservoir heights than are required with a conventional "Sylgard seal" pipet. The bath was either isosmotic to the perfusate, or was made 300 mOsm hyperosmotic using urea. Net water reabsorption did not occur in tubules perfused at low pressure (average reservoir height = 26 cm H2O) even when the bath was hyperosmotic: delta Jv = -0.06 +/- 0.18 nl/min (n = 7). Observed increases in sodium concentration and osmolality of collected fluid, when the bath was made hyperosmotic, were 16 +/- 8 mM (n - 7) and 254 +/- 38 mOsm (n = 7), respectively. Presumably the large increase in osmolality of the collected fluid was due to entrance of urea. When the "Sylgard seal" collecting end was utilized higher perfusion reservoir heights had to be used to maintain flow (mean height 66 cm H2O). These tubules were highly permeable to water as reported by others for this tubule segment. In the presence of a hyperosmotic bath water extrusion resulted in a dramatic increase in the osmolality of the collected fluid (312 +/- 5 mOsm; 7 tubules) which was almost completely accounted for by an increase in sodium concentration (153 +/- 8 mmole/l; 6 tubules). The 14C urea permeability (measured lumen to bath) of descending limbs in a 300 mOsm bath was 0.64 x 10(-7) cm2 . s-1 +/- 0.23 x 10(-7) (11 tubules). When the bath was made hyperosmotic using urea or raffinose the 14C urea permeability increased significantly.

Animals↗