Search PubMed⌕ Search

Biomedical subjects

R K Jain

Publications and source records attributed to R K Jain.

At least 19 recordsLinked to original sources
PubMed1996

Tumor angiogenesis and interstitial hypertension.

Due to the high permeability of tumor vessels to fluids and plasma proteins, the microvascular pressure (MVP) is the principal driving force for interstitial hypertension in solid tumors; as a result, hydrostatic pressures between the microvascular and interstitial space are close to equilibrium. Based on these observations, we hypothesized that the tumor interstitial fluid pressure (IFP) should increase following the onset of angiogenesis. To this end, the relationship between IFP and tumor neovascularization was determined in the human colon adenocarcinoma (LS174T) and the murine carcinoma (MCaIV) implanted in a transparent dorsal skin fold chamber in severe combined immunodeficient mice. Three stages in the development of the tumor neovasculature were characterized by intravital microscopy. Stage I tumors were avascular, stage II was characterized by vascular sprouts and loops, and in stage III, the tumor vasculature was completely developed and blood flow was obvious. The IFP was measured with micropipettes and a servo-null system. For both tumor types, the IFP in stage I tumors was close to 0 mm Hg, and IFP increased significantly from one stage to the next. To further confirm that interstitial hypertension was associated with the development of the tumor vasculature, IFP was measured in LS174T spheroids. The mean pressure in spheroids was 0.2 +/- 0.3 mm Hg. In stage III tumors, the IFP was compared to the MVP. In MCaIV, the MVP was comparable to the IFP; however, in LS174T the MVP was significantly higher than the IFP. In conclusion, the results demonstrate that avascular tumors have atmospheric pressures and that tumor interstitial hypertension is associated with the development of the neovasculature.

Adenocarcinoma↗
PubMed1996

Fenvalerate (alpha-cyano-m-phenoxy-benzyl alpha-isopropyl-p-chlorophenyl acetate) residues in and on okra fruits.

Okra crop was sprayed with sumicidin 20E (Fenvalerate 20% EC) at the rate of 300 ml/ha (C1), 375 ml/ha (C2) and 500 ml/ha (C3). Residues in fruit samples were determined by gas chromatography (Hewlett Packard 5890 A) at different time intervals to establish the safe waiting period for Fenvalerate. The initial deposits of Fenvalerate on okra fruits for C1, C2 and C3 were 1.4 ppm, 2.8 ppm and 4.5 ppm, respectively. Seven days after spraying, the initial deposits of C1, C2 and C3 decreased to 0.03 ppm, 0.05 ppm and 0.67 ppm, respectively. The residue values of Fenvalerate on okra fruits 7 days after spraying were below the tolerance limit (0.2 ppm; Anonymous, 1978; FAO, 1980) for C1 and C2, but above it in the case of C3. Ten days after spraying, the residue values of C1, C2 and C3 were below the tolerance limit.

Chromatography, Gas↗
PubMed1996

Physiologically based kinetic model of effector cell biodistribution in mammals: implications for adoptive immunotherapy.

The goal of the present investigation was to develop a physiologically based kinetic model to describe the biodistribution of immunologically active effector cells in normal and neoplastic tissues of mammals based on the current understanding of lymphocyte trafficking pathways and signals. The model was used to extrapolate biodistribution among different animal species and to identify differences among different effector populations and between intra-arterial and systemic injections. Most importantly, the model was used to discern critical parameters for improving the delivery of effector cells. In the model, the mammalian body was divided into 12 organ compartments, interconnected in anatomic fashion. Each compartment was characterized by blood flow rate, organ volume and lymphatic flow rate, and other physiological and immunological parameters. The resulting set of 45 differential equations was solved numerically. The model was used to simulate the following biodistribution data: (a) nonactivated T lymphocytes in rats; (b) interleukin 2-activated tumor-infiltrating lymphocytes in humans; (c) nonactivated natural killer (NK) cells in rats; and (d) interleukin 2-activated adherent NK cells in mice. Comparisons between simulations and data demonstrated the feasibility of the model and the scaling scheme. The similarities as well as differences in biodistribution of different lymphocyte populations were revealed as results of their trafficking properties. The importance of lymphocyte infiltration from surrounding normal tissues into tumor tissue was found to depend on lymphocyte migration rate, tumor size, and host organ. The study confirmed that treatment with effector cells has not been as impressive as originally promised, due, in part, to the biodistribution problems. The model simulations demonstrated that low effector concentrations in the systemic circulation greatly limited their delivery to tumor. This was due to high retention in normal tissues, especially in the lung. Reducing normal tissue retention through decreasing attachment rate or adhesion site density in the lung by 50% could increase the tumor uptake by approximately 40% for tumor-infiltrating lymphocytes and by approximately 60% for adherent NK cells. Our analysis suggested the following strategies to improve effector cell delivery to tumor: (a) bypassing the initial lung entrapment with administration to the arterial supply of tumor; (b) reducing normal tissue retention using effector cells with high deformability or blocking lymphocyte adhesion to normal vessels; and (c) enhancing tumor-specific capture and arrest by modifying the tumor microenvironment.

Animals↗
PubMed1996

Plasmid-encoded degradation of p-nitrophenol by Pseudomonas cepacia.

A Pseudomonas cepacia strain RKJ 200 capable of utilising p-nitrophenol (PNP+) as the sole source of carbon, nitrogen, and energy was isolated by selective enrichment. The degradation of PNP by this strain proceeds through an oxidative route as indicated by the accumulation of nitrite molecules in the culture medium. Initial studies indicate that the degradation of PNP occurs via hydroquinone as shown by thin layer chromatography and gas chromatography studies; hydroquinone is further degraded via the beta-ketoadipate pathway. A plasmid of approximately 50 kilobase pairs was found to be responsible for carrying genes for PNP degradation in this strain. This was based on the facts that the PNP- mutants lacked the plasmid and that the PNP+ phenotype could conjugally be transferred. In addition, the same plasmid also encoded resistance to inorganic zinc ions.

Biotransformation↗
PubMed1996

Characterization of the specificities of human blood group H gene-specified alpha 1,2-L-fucosyltransferase toward sulfated/sialylated/fucosylated acceptors: evidence for an inverse relationship between alpha 1,2-L-fucosylation of Gal and alpha 1,6-L-fucosylation of asparagine-linked GlcNAc.

The assembly of complex structures bearing the H determinant was examined by characterizing the specificities of a cloned blood group H gene-specified alpha 1,2-L-fucosyltransferase (FT) toward a variety of sulfated, sialylated, or fucosylated Gal beta 1,3/4GlcNAc beta- or Gal beta 1,3GalNAc alpha-based acceptor structures. (a) As compared to the basic type 2, Gal beta 1,4GlcNAc beta-(K(m) = 1.67 mM), the basic type 1 was 137% active (K(m) = 0.83 mM). (b) On C-6 sulfation of Gal, type 1 became 142.1% active and type 2 became 223.0% active (K(m) = 0.45 mM). (c) On C-6 sulfation of GlcNAc, type 2 showed 33.7% activity. (d) On C-3 or C-4 fucosylation of GlcNAc, both types 1 and 2 lost activity. (e) Type 1 showed 70.8% and 5.8% activity, respectively, on C-6 and C-4 O-methylation of GlcNAc. (f) Type 1 retained 18.8% activity on alpha 2,6-sialylation of GlcNAc. (g) Terminal type 1 or 2 of extended chain had lower activity. (h) With Gal in place of GlcNAc in type 1, the activity became 43.2%. (i) Compounds with terminal alpha 1,3-linked Gal were inactive. (j) Gal beta 1,3GalNAc alpha- (the T-hapten) was approximately 0.4-fold as active as Gal beta 1,4GlcNAc beta-. (k) C-6 sulfation of Gal on the T-hapten did not affect the acceptor activity. (l) C-6 sulfation of GalNAc decreased the activity to 70%, whereas on C-6 sulfation of both Gal and GalNAc the T-hapten lost the acceptor ability. (m) C-6 sialylation of GalNAc also led to inactivity. (n) beta 1,6 branching from GalNAc of the T-hapten by a GlcNAc residue or by units such as Gal beta 1, 4GlcNAc-, Gal beta 1,4(Fuc alpha 1,3)GlcNAc-, or 3-sulfoGal beta 1,4GlcNAc- resulted in 111.9%, 282.8%, 48.3%, and 75.3% activities, respectively. (o) The enhancement of enzyme affinity by a sulfo group on C-6 of Gal was demonstrated by an increase (approximately 5-fold) in the K(m) for Gal beta 1,4GlcNAc beta 1,6(Gal beta 1,3)GalNAc alpha-O-Bn in presence of 6-sulfoGal beta 1,- 4GlcNAc beta-O-Me (3.0 mM). (p) Among the two sites in Gal beta 1, 4GlcNAc beta 1,6(Gal beta 1,3) GalNAc alpha-O-Bn, the enzyme had a higher affinity ( > 3-fold) for the Gal linked to GlcNAc. (q) With respect to Gal beta 1,- 3GlcNAc beta-O-Bn (3.0 mM), fetuin triantennary asialo glycopeptide (2.4 mM), bovine IgG diantennary glycopeptide (2.8 mM), asialo Cowper's gland mucin (0.06 mM), and the acrylamide copolymers (0.125 mM each) containing Gal beta 1,3GlcNAc beta-, Gal beta 1,3(6-sulfo)GlcNAc beta-, Gal beta 1,3GalNAc alpha-, Gal beta 1,3Gal beta-, or Gal alpha 1,3Gal beta- units were 153.6%, 43.0%, 6.2%, 52.5%, 94.9%, 14.7%, 23.6%, and 15.6% active, respectively. (r) Fucosylation by alpha 1,2-L-FT of the galactosyl residue which occurs on the antennary structure of the bovine IgG glycopeptide was adversely affected by the presence of an alpha 1,6-L-fucosyl residue located on the distant glucosaminyl residue that is directly attached to the asparagine of the protein backbone. This became evident from the 4-fold activity of alpha 1,2-L-FT toward bovine IgG glycopeptide after approximately 5% removal of alpha 1,6-linked Fuo.

ABO Blood-Group System↗
PubMed1996

Specificity analysis of three clonal and five non-clonal alpha 1,3-L-fucosyltransferases with sulfated, sialylated, or fucosylated synthetic carbohydrates as acceptors in relation to the assembly of 3'-sialyl-6'-sulfo Lewis x (the L-selectin ligand) and related complex structures.

Unique specificities of the cloned alpha 1,3-L-fucosyltransferases (FTs), FT III (Lewis type), FT IV (myeloid type), and FT V (plasma type), and the alpha 1,3-FTs of Colo 205 (colon carcinoma), HL 60 (myeloid), B142 (lymphoid), EKVX (lung carcinoma), and calf mesenteric lymph nodes (CMLN) were discerned with sulfated, sialylated, and/or fucosylated Gal beta 1,3/4GlcNAc beta-based acceptor moieties. (a) FT V was 1.0-, 20.8-, and 4.6-fold active in forming Lewis x, Lewis y, and 3'-alpha-galactosyl Lewis x, respectively. (b) FT III and FT V formed approximately 4-fold 3'-sulfo Lewis x, as compared to 3'-sialyl Lewis x. (c) FT IV showed great efficiency in forming 3'-sulfo Lewis x (249%) and Lewis x (345%) in mucin-type branched chains. (d) FT III, FT IV, and FT V formed 19%, 62%, and 47% 6-sulfo Lewis x as compared to Lewis x. (e) 6'-Sulfo Lewis x and 3'-sialyl-6'-sulfo Lewis x (GLYCAM ligand) were not synthesized from their immediate precursors by FT III, FT IV, or FT V. (f) FT III, FT IV, and FT V were 311%, 9%, and 188% active, respectively, with 2'-fucosyl lactose but were not active with 2'- fucosyl-6'-sulfo lactose. (g) FT III and FT V were 7.0- and 0.5-fold active in forming Lewis a as compared to Lewis x, whereas, FT IV was inactive. (h) FT III was -2.0-fold more active in forming 3'-alpha-galactosyl Lewis a than Lewis b. (i) FT III synthesized 6-sialyl Lewis a (40% efficiency as compared to Lewis a) from 6-sialyl type 1. (j) FT III did not act on 6'-sulfo or 6'-sialyl type 1 but was 106% and 22% active with 3'-sulfo and 6-sulfo type 1, respectively. (k) The Colo 205 FT activities with type 1 compounds almost paralleled that of FT III except for the low activity (9%) with Gal beta 1,3(NeuAc alpha 2, 6)GlcNAc beta-O-Bn, but with type 2 considerable differences between Colo 205 FT and FT III were noticed. (l) The alpha 1,3-FTs of CMLN, HL60, B142, and EKVX were 1.2-1.7 times active with Fuc alpha 1,2Gal beta 1,4GlcNAc beta- O-pNP and Gal alpha 1,3Gal beta 1,4 GlcNAc beta-O-Bn with respect to Gal beta 1,4GlcNAc beta-O-Al. (m) Both CMLN and HL60 FTs were 2-fold active with 3-sulfoGal beta 1,4GlcNAc in a mucin-type branch structure such as 3-sulfoGal beta 1,4GlcNAc beta 1,6(Gal beta 1,3)GalNAc alpha-O-Bn. (n) The 3'-sulfoLacNAc/acrylamide copolymer, either as an acceptor or as a competitive inhibitor, had the potential to distinguish myeloid type alpha 1,3-FT from the plasma type.

Animals↗
PubMed1996

Plasmid-mediated degradation of o-phthalate and salicylate by a Moraxella sp.

A Moraxella sp. strain VG45 capable of utilizing o-phthalate and salicylate as a sole source of carbon and energy was isolated. The degradation of o-phthalate occurs via phthalate 4,5-dioxygenase, 4,5-dihydro-4,5-dihydroxyphthalate dehydrogenase, 4,5-dihydroxyphthalate decarboxylase and protocatechuate 4,5-dioxygenase. Salicylate is degraded via salicylate 5-hydroxylase, gentisate 1,2-dioxygenase and then by a glutathione-independent maleylpyruvate hydrolase. Further, a plasmid of app. 60 kilobase pairs (kb) is involved in the degradation of the o-phthalate and salicylate and the enzymes of these two pathways are independently regulated in strain VG45.

Biodegradation, Environmental↗
PubMed1996

Effect of radiation on interstitial fluid pressure and oxygenation in a human tumor xenograft.

Elevated interstitial fluid pressure (IFP) is a pathophysiological characteristic of most human and experimental tumors and may be responsible, in part, for the poor distribution of blood-borne therapeutic agents and low blood flow rate in tumors. Recent data in cervical carcinomas in patients suggest that fractionated radiation can lower tumor IFP and increase oxygen partial pressure (pO (2)) in some patients. The goals of this study were to find the minimum dose of radiation required to modulate IFP and pO(2) and to determine the time course of IFP changes due to radiation in a preclinical model. Xenografts of the LS174T human colon adenocarcinoma were grown in the right flank of nude (BALB/c) mice. IFP and pO(2) were measured before and 24 h after graded doses of irradiation. The mean +/- SD initial IFP in untreated tumors was 12.9 +/- 0.5 mm Hg (n=109), and the range was 3.0 to 40.3 mm Hg. The mean +/- SD and median initial pO(2) were 20.2 +/- 2.4 and 11.9 mm Hg, respectively (n=37). IFP and pO(2) were independent of tumor size. Fractionated radiation lowered IFP by 2.5 mm Hg when the total dose was 10 or 15 Gy (P<0.05), but IFP did not change in the controls or the 5-Gy radiation group (P>0.05). Irradiation increased the proportion of tumors at higher oxygen tensions when compared to control tumors. The IFP and tumor volumes were followed for up to 10 days after a single dose of 10, 20, or 30 Gy of irradiation. IFP decreased for all treatment groups. The decrease was most significant for the group receiving 30 Gy. On day five following irradiation, the IFP had decreased by 35%. The changes in IFP and pO(2) occurred before any macroscopic changes in tumor volume could be observed. The radiation-induced decrease in IFP could be, in part, responsible for the increased uptake of monoclonal antibodies following single or fractionated radiation that has been reported in the literature.

Adenocarcinoma↗
PubMed1996

Chemical synthesis of a hexasaccharide comprising the Lewisx determinant linked beta-(1-->6) to a linear trimannosyl core and the precursor pentasaccharide lacking fucose.

Phenyl 2,3,4-tri-O-acetyl-6-O-chloroacetyl-1-thio-alpha,beta-mannopyranoside (5) was condensed with benzyl O-(2,3,4-tri-O-benzyl-beta-D-mannopyranosyl)-(1-->6)-2,3,4-tri-O-benzyl- alpha-D- mannopyranoside (12) in the presence of NIS-triflic acid to give, after removal of the chloroacetyl group, the key intermediate, benzyl O-(2,3,4-tri-O-acetyl-alpha-D-mannopyranosyl)-(1-->6)-O-(2,3,4-tri-O-ben zyl- beta-D-mannopyranosyl)-(1-->6)-2,3,4-tri-O-benzyl-alpha-D-mannopyranosid e (14). A similar condensation of 6 and 7 with acceptor 14, followed by the removal of protecting groups, afforded 16 and 18, respectively. These compounds are expected to be useful in specificity studies of an antibody raised against a related, synthetic antigen that we are currently investigating.

Antigens, CD↗
PubMed1996

Synthesis of precursors for the dimeric 3-O-SO3Na Lewis X and Lewis A structures.

Stereoselective syntheses of 3-O-SO3Na-beta-Gal-(1-->4)-beta-GlcNAc- (1-->3)-beta-Gal-(1-->4)-GlcNAc-beta-OBn (15) and 3-O-SO3Na-beta-Gal-(1-->3)-beta-GlcNAc-(1-->3)-beta-Gal-(1-->3)- beta-GlcNAc-(1-->3)-beta-Gal-(1-->4)-Glc-beta-OBn (25) were accomplished through the use of two novel glycosyl donors, namely, ethyl O-(2,6-di-O-acetyl-3,4-O-isopropylidene-beta-D- galactopyranosyl)-(1-->4)-3-O-acetyl-2-deoxy-2-phthalimido-1-thio-6-O- trimethylacetyl-beta-D-glucopyranoside (8). and ethyl O-(2,6-di-O-acetyl-3,4-O-isopropylidene-beta-D-galactopyranosyl)- (1-->3)-4-O-acetyl-2-deoxy-2-phthalimido-1-thio-6-O-trimethylace tyl-beta-D-glucopyranoside (18).

CA-19-9 Antigen↗
PubMed1996

Oxygenation in tumors by modified hemoglobins.

The effect of systemic injection of modified hemoglobin (Hb) prepared from bovine, human, or mouse Hb on tumor oxygenation was investigated. Hb was modified by (1) diisothiocyanatobenzenesulfonate (DIBS) to yield cross-linking within a tetramer; (2) glycolaldehyde (Glyal) to yield cross-linking between and within tetramers; (3) carboxymethylation (Cm) to change oxygen affinity; or (4) poly(ethylene glycol) (PEG) to yield attachment between tetramers. HGL9 (human glioma) in nude mice and FSaII (mice fibrosarcoma) in C3H mice were used as tumor models. Dose and time dependency were detected in the oxygenation effect by bovine-PEG-Hb. Internal cross-linkage prolonged the half-life in the circulation, and thus showed a significant effect. Compared to bovine-CmHb, bovine-DIBS-Hb and bovine-DIBS-CmHb were more effective. Decreasing the oxygen affinity by Cm significantly enhanced tumor oxygenation. Human-DIBS-CmHb was more effective than human-DIBS-Hb. These effects were caused by oxygen carrying capacity of modified Hbs as well as hemodynamic factors, and the injection seemed to reduce both perfusion-limited (acute) and diffusion-limited (chronic) hypoxia.

Animals↗
PubMed1996

Intussusceptive microvascular growth in a human colon adenocarcinoma xenograft: a novel mechanism of tumor angiogenesis.

Intussusceptive microvascular growth refers to vascular network formation by insertion of interstitial tissue columns, called tissue pillars or posts, into the vascular lumen and subsequent growth of these columns, resulting in partitioning of the vessel lumen. While intussusception has been reported in normal developing organs, its existence in solid tumors has not been previously documented. By observing the growth of the human colon adenocarcinoma (LS174T) in vivo for a period of 6 weeks, we demonstrate that intussusception is an important mechanism of tumor angiogenesis. At the leading edge of the tumor, vascular growth was found to occur by both intussusception and endothelial sprouting. In the stabilized regions, intussusception led to network remodeling and occlusion of vascular segments. The formation of some tissue pillars appears to depend on intravascular blood-flow patterns or changes in intravascular shear stress. The rapid vascular remodeling by intussusception could possibly contribute to intermittent blood flow in tumors.

Adenocarcinoma↗
PubMed1996

Effect of transvascular fluid exchange on pressure-flow relationship in tumors: a proposed mechanism for tumor blood flow heterogeneity.

Tumor blood flow (TBF) is characterized by spatial and temporal heterogeneities. Despite the crucial role of TBF in tumor growth, metastasis, and therapy, the mechanisms underlying these heterogeneities are not fully understood. Tumor vessels are, in general, more leaky than normal vessels and this may enhance the efficiency of fluid exchange between the vascular and the interstitial space. The coupling between transvascular fluid exchange and hemodynamics in tumors has not been explored previously. To investigate the role of transvascular fluid exchange on afferent and efferent blood flow, we modeled the tumor vasculature as an equivalent single vessel which is permeable and deformable and embedded in a fluid medium with uniform pressure. Simulations were carried out to examine the effects of vessel leakiness, vessel compliance, and interstitial fluid pressure on (a) pressure-flow relationship, (b) arterial-venous pressure relationship, and (c) pressure profile along the vessel. Experiments suggested by model simulations required an independent control of arterial and venous pressure and tumor blood flow. To this end, we perfused tissue-isolated tumors ex vivo and obtained data on perfusate flow rate vs arterial and venous pressures. The simulations predicted the following trends as a result of an enhanced fluid filtration across the vessel wall: (a) for a fixed arterial-venous pressure difference, efferent flow decreases with increasing venous pressure, (b) changes in venous pressure are not completely transmitted to the arterial side, and (c) the pressure profile along the vessel becomes less steep. The experimental results confirmed these trends and indicated that vascular and interstitial flow are coupled in isolated tumors. The implications of this coupling for the spatial and temporal heterogeneity in TBF are discussed.

Adenocarcinoma↗
PubMed1996

Leukocyte-endothelial adhesion and angiogenesis in tumors.

Leukocyte-endothelial adhesion and angiogenesis, until recently considered as separate processes, have been shown to be linked by two recent findings: soluble cellular adhesion molecules (CAMs) involved in leukocyte-endothelial interactions are angiogenic and well known angiogenic molecules secreted by cancer or immune. cells can modulate the endothelial CAMs. This molecular link may partially explain why the overall leukocyte-endothelial interaction is often low and heterogeneous in angiogenic tumor vessels and why activated lymphocytes adhere nonuniformly to tumor vessels when injected into the tumor's blood supply.

Animals↗
PubMed1996

Role of erythrocytes in leukocyte-endothelial interactions: mathematical model and experimental validation.

The binding of circulating cells to the vascular wall is a central process in inflammation, metastasis, and therapeutic cell delivery. Previous in vitro studies have identified the adhesion molecules on various circulating cells and the endothelium that govern the process under static conditions. Other studies have attempted to simulate in vivo conditions by subjecting adherent cells to shear stress as they interact with the endothelial cells in vitro. These experiments are generally performed with the cells suspended in Newtonian solutions. However, in vivo conditions are more complex because of the non-Newtonian flow of blood, which is a suspension consisting of 20-40% erythrocytes by volume. The forces imparted by the erythrocytes in the flow can contribute to the process of cell adhesion. A number of experimental and theoretical studies have suggested that the rheology of blood can influence the binding of circulating leukocytes by increasing the normal and axial forces on leukocytes or the frequency of their collision with the vessel wall, but there have been no systematic investigations of these phenomena to date. The present study quantifies the contribution of red blood cells (RBCs) in cell capture and adhesion to endothelial monolayers using a combination of mathematical modeling and in vitro studies. Mathematical modeling of the flow experiments suggested a physical mechanism involving RBC-induced leukocyte dispersion and/or increased normal adhesive contact. Flow chamber studies performed with and without RBCs in the suspending medium showed increases in wall collision and binding frequencies, and a decrease in rolling velocity in the presence of erythrocytes. Increased fluid viscosity alone did not influence the binding frequency, and the differences could not be attributed to large near-wall excesses of the lymphocytes. The results indicate that RBCs aid in the transport and initial engagement of lymphocytes to the vascular wall, modifying the existing paradigm for immune cell surveillance of the vascular endothelium by adding the erythrocyte as an essential contributor to this process.

Biophysical Phenomena↗
PubMed1996

Hindered diffusion in agarose gels: test of effective medium model.

The diffusivities of uncharged macromolecules in gels (D) are typically lower than in free solution (D infinity), because of a combination of hydrodynamic and steric factors. To examine these factors, we measured D and D infinity for dilute solutions of several fluorescein-labeled macromolecules, using an image-based fluorescence recovery after photobleaching technique. Test macromolecules with Stokes-Einstein radii (rs) of 2.1-6.2 nm, including three globular proteins (bovine serum albumin, ovalbumin, lactalbumin) and four narrow fractions of Ficoll, were studied in agarose gels with agarose volume fractions (phi) of 0.038-0.073. The gels were characterized by measuring the hydraulic permeability of supported agarose membranes, allowing calculation of the Darcy permeability (kappa) for each gel sample. It was found that kappa, which is a measure of the intrinsic hydraulic conductance of the gel, decreased by an order of magnitude as phi was increased over the range indicated. The diffusivity ratio D/D infinity, which varied from 0.20 to 0.63, decreased with increases in rs or phi. Thus as expected, diffusional hindrances were the most severe for large macromolecules and/or relatively concentrated gels. According to a recently proposed theory for hindered diffusion through fibrous media, the diffusivity ratio is given by the product of a hydrodynamic factor (F) and a steric factor (S). The functional form is D/D infinity = F(rs/k1/2) S(f), where f = [(rs+rf)/rf]2 phi and rf is the fiber radius. Values of D/D infinity calculated from this effective medium theory, without use of adjustable parameters, were in much better agreement with the measured values than were predictions based on other approaches. The strengths and limitations of the effective medium theory for predicting diffusivities in gels are discussed.

Animals↗