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At least 307 records · Page 17Linked to original sources
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↗
PubMed1983

[New chromatography. Technics for the isolation and separation of natural products].

Besides high-performance liquid chromatography (HPLC) which is now a well-established and currently used technique, several emerging methods for the isolation and separation of natural products are receiving considerable attention. Centrifugal thin-layer chromatography is a very rapid technique, but limited in resolution. Of special interest are the recently developed support-free liquid-liquid chromatography methods such as droplet counter-current chromatography (DCCC) and rotation locular counter-current chromatography (RLCC). This latter method was applied to the separation of the enantiomers of (+/-)-norephedrine.

Chromatography↗
PubMed1989

Fixation with even small quantities of glutaraldehyde affects red blood cell surface properties in a cell- and species-dependent manner. Studies by cell partitioning.

Partitioning in charge-sensitive dextran-poly(ethylene glycol) aqueous phase systems reveals that fixation with even small concentrations of glutaraldehyde (e.g., 0.1% w/v) changes the surface properties of cells. While fixation with larger concentrations of glutaraldehyde (i.e., 1.85%) increases erythrocyte partition ratios, the effect of lower glutaraldehyde concentrations on the partition ratios appears to be species-specific. The differential effect of glutaraldehyde on rat reticulocytes and erythrocytes indicates that fixation is also cell-dependent. These data, together with the previous report that glutaraldehyde fixation does not change the characteristic relative partition ratios of rat mature erythrocytes of different cell ages, suggest that the nature and extent of glutaraldehyde alteration of cell surfaces must, in each case, be empirically evaluated.

Aldehydes↗
PubMed1989

Analysis by partitioning in aqueous two-phase systems of the loss of transferrin-binding capacity during maturation of rat reticulocytes.

A decrease in the number of binding sites for 125I-transferrin, without an apparent modification of the association constant, has been observed during the maturation of reticulocytes into erythrocytes. As an experimental model, different red cell populations from phenylhydrazinic anaemic rates (95% to 12% reticulocyte-rich) have been used. The fractionation by multiple partition in two-phase systems of these red cell populations has been applied here to show the relationship between number of transferrin receptors and rate of reticulocyte maturation.

Anemia↗