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Biomedical subjects

K Burdzy

Publications and source records attributed to K Burdzy.

10 recordsLinked to original sources
PubMed2001

Mechanisms for facilitated target location and the optimal number of molecules in the diffusion search process.

We investigate the number N of molecules needed to perform independent diffusion in order to achieve bonding of a single molecule to a specific site in time t(0). For a certain range of values of t(0), an increase from N to kN molecules (k>1) results in the decrease of search time from t(0) to t(0)/k. In this regime, increasing the number of molecules is an effective way of speeding up the search process. However when N> or =N0 (optimal number of N) the reduction of time from t(0) to t(0)/k can be achieved only by an exponentially large increase in the number of molecules [from N to N exp(ck) for some c>0].

Binding Sites↗
PubMed1999

Diffusion on curved, periodic surfaces.

We present a simulation algorithm for a diffusion on a curved surface given by the equation phi(r)=0. The algorithm is tested against analytical results known for diffusion on a cylinder and a sphere, and applied to the diffusion on the P, D, and G periodic nodal surfaces. It should find application in an interpretation of two-dimensional exchange NMR spectroscopy data of diffusion on biological membranes.

Journal Article↗
PubMed1993

Proteases are implicated in the changes in the Sertoli cell cytoskeleton elicited by follicle-stimulating hormone or by dibutyryl cyclic AMP.

Follicle-stimulating hormone (FSH) or dibutyryl cyclic AMP (dbcAMP) elicits striking morphological changes in Sertoli cells in culture in serum-free medium, resulting in a transition from an epithelial type of cell association pattern to that of an astrocytic or fibroblast-like cell, with attenuated cytoplasmic extensions between cells, and with diminished F-actin stained stress fibers. These responses of Sertoli cells do not occur in the presence of normal untreated serum, but they do take place in the presence of acid-treated serum which is depleted of antiproteases. The addition of alpha 2-macroglobulin to serum-free medium or to antiprotease-depleted serum resulted in the blockage of morphological responses of Sertoli cells to FSH or to dbcAMP. Changes in pattern of arrangements of F-actin in Sertoli cells in culture, which occur in response to FSH or to dbcAMP, were also prevented by the presence of alpha 2-macroglobulin. Thus, the diminution in bundles of F-actin containing stress fibers, which otherwise takes place in Sertoli cells stimulated by FSH or by dbcAMP, did not occur in cells in culture in the presence of alpha 2-macroglobulin, in the presence or absence of acid-treated serum. The inhibiting effects of dbcAMP on the migration of Sertoli cells in serum-free medium became nondetectable in medium containing normal untreated serum, but remained evident in Sertoli cells in culture in medium containing acid-treated serum depleted of antiproteases. Addition of alpha 2-macroglobulin blocked the inhibitory effects of dbcAMP on Sertoli cell migration. Similarly, the presence of alpha 2-macroglobulin prevented the inhibitory effects of dbcAMP on the contractility of TM4 cells which had been embedded in collagen type-I and incubated in serum-free medium. We discuss the possibility that cellular proteases may be implicated in the disintegration of microfilament bundles, either by favoring depolymerization of actin filaments; by facilitating breakage of the link of the transmembrane molecular assembly between cytoskeletal extracellular matrix components; or by catalyzing a disruption of the modular organization of one or more of the actin cross-linking proteins. By inference, we postulate that morphological responses of Sertoli cells to FSH require the activation of cellular proteases for one or more of these reactions, and that alpha 2-macroglobulin blocks the Sertoli cell morphological responses to FSH by inhibiting the proteases involved.

Actins↗
PubMed1992

Competition between cell-substratum interactions and cell-cell interactions.

Clusterin, a glycoprotein which elicits the aggregation of a wide variety of cells (Fritz, I. B., and Burdy, K.:J. Cell Physiol., 140:18-28, 1989), has been utilized to investigate some of the factors modulating the competition between cell-substratum interactions and cell-cell interactions. We compared the responses to clusterin by anchorage-independent cells (erythrocytes) with those by anchorage-dependent TM4 cells (a cell line derived from neonatal mouse testis cells). Cells were maintained in culture in the presence of various substrata chosen to enhance cell-substratum interactions (laminin-coated wells), or to diminish cell-substratum interactions (agarose-coated wells). Results obtained showed that the aggregation of erythrocytes elicited by clusterin was independent of the nature of the substratum. In contrast, clusterin addition resulted in aggregation of anchorage-dependent TM4 cells only when TM4 cell-substratum interactions were weak. Thus, clusterin did not aggregate TM4 cells plated upon a laminin substratum, but readily aggregated TM4 cells plated upon an agarose-coated substratum, independent of the sequence of addition of cells and clusterin to the culture dish. We utilized YIGSR, a peptide which competes with laminin for laminin receptors, to determine the possible role of laminin receptors on TM4 cells in the competition between cell-substratum interactions and cell-cell interactions. The presence of YIGSR did not alter responses of erythrocytes to clusterin under all conditions examined. In contrast, the responses of TM4 cells to clusterin were greatly changed. YIGSR addition resulted in the inhibition of aggregation of TM4 cells otherwise elicited by clusterin. YIGSR also prevented attachment of TM4 cells to a laminin-coated surface, but this was reversed by the presence of clusterin. We discuss the possible roles of clusterin and laminin in altering the balance in the competition between cell to cell interactions and cell to substratum interactions.

Animals↗
PubMed1991

Clustering of erythrocytes by fibrinogen is inhibited by carnitine: evidence that sulfhydryl groups on red blood cell membranes are involved in carnitine actions.

Carnitine is bound by intact red blood cells, by red blood cell ghosts, and by glutaraldehyde-fixed human erythrocytes in a non-saturable, temperature-dependent manner. Binding of carnitine by these preparations is blocked by sulfhydryl reagents. Incubation or preincubation of red blood cell preparations with carnitine inhibits the aggregation of erythrocytes otherwise elicited by fibrinogen. Identical effects are obtained with red blood cell ghosts. In contrast, choline, even at high concentrations, is inactive in preventing the aggregation of erythrocytes. We discuss possible mechanisms by which carnitine favors the dispersion of red blood cells, and we present data indicating that sulfhydryl groups on erythrocyte membranes are required to permit these carnitine actions to be manifested.

Carnitine↗
PubMed1991

High-resolution scanning electron micrographs of freeze-cracked cells in testes from normal and irradiated rats at different stages of gonadal development.

Newly developed techniques in high-resolution scanning electron microscopy (SEM) and for tissue-processing procedures have been applied to an investigation of structures of various cells in rat testes at different stages of gonadal maturation. A series of high-resolution SEM micrographs are presented which survey the surfaces of different types of testis cells during normal development, and which also illustrate ultrastructural features of some of their intracellular organelles. In addition, a series of high-resolution SEM micrographs are presented which compare the structural features of Sertoli cells in normal testes with those in germ-cell-depleted testes obtained from rats killed at varying times after having been irradiated in utero. We describe our observations on the structural properties of surfaces and intracellular organelles in Sertoli cells, Leydig cells, peritubular myoid cells, and some classes of germinal cells. We also consider the possible role of Sertoli cell apical cytoplasmic processes in lumen formation. Similarities are pointed out between the structure of germ-cell-depleted testes, resulting from irradiation in utero, and the structure of germ-cell-depleted testes in seasonal breeders during periods of involution. Finally, we discuss advantages and disadvantages of methods employed to reveal the fine structure of intracellular organelles in cells of the testis.

Animals↗
PubMed1989

Novel action of carnitine: inhibition of aggregation of dispersed cells elicited by clusterin in vitro.

A novel effect of carnitine and O-acylcarnitine derivatives has been described. The presence of these compounds has been shown to inhibit the aggregation of erythrocytes otherwise elicited by the addition of clusterin or fetuin. The specificity of carnitine action has been investigated by comparing influences of chemically related compounds. The concentrations required for inhibition by approximately 50% of aggregation of erythrocytes by clusterin under in vitro conditions defined were determined to be 1.5 mM for L(-) or D(+) enantiomers of carnitine; 0.5 mM for decanoyl(-)- or (+)-carnitine; 0.13 mM for lauroyl(-)- or (+)-carnitine, and 0.05 mM for myristoyl(-)- or (+)-carnitine. In contrast, concentrations up to 12.5 mM of dimethylcarnitine, deoxycarnitine, acetylcholine, acetyl-beta-methylcholine, or inositol had no detectable inhibitory effect on aggregation elicited by clusterin. Clusterin addition also resulted in the aggregation of three other cell types examined (guinea pig spermatozoa, a cell line derived from testes of neonatal mice called TM4 cells, and Sertoli cells from testes of 20 day-old rats). As in the case with erythrocytes, the presence of carnitine inhibited aggregation of spermatozoa, TM4 cells, and Sertoli cells in suspension. We consider possible mechanisms by which carnitine inhibits aggregation of erythrocytes and other populations of dispersed cells incubated in the presence of clusterin.

Animals↗
PubMed1983

Purification and characterization of a cell-aggregating factor (clusterin), the major glycoprotein in ram rete testis fluid.

Clusterin has been purified from ram rete testis fluid by conventional techniques and by immunoaffinity chromatography. The molecule is characterized as a glycoprotein having a molecular mass of approximately 80,000 Da and an isoelectric point of 3.6. The purified protein retains the capacity to elicit clustering of cells in an in vitro assay. Under reducing conditions in the presence of sodium dodecyl sulfate, clusterin dissociates into subunits of about 40,000 Da. Heterogeneities in apparent molecular mass were eliminated after treatment of clusterin with neuraminidase. Gel filtration chromatography revealed that clusterin exists in dimeric and tetrameric forms under conditions of neutral pH and low salt concentrations. In the presence of 6 M urea, only the monomeric form is evident, with an apparent molecular mass of approximately 85,000 Da. Clusterin, which was found to contain 4.5% glucosamine, binds to concanavalin A-Sepharose and also to wheat germ agglutinin Sepharose. The amino acid composition of clusterin is reported. The possible cellular source of clusterin in rete testis fluid is discussed. It is shown that Sertoli cells in the seminiferous tubule are one potential source, since primary cultures of rat Sertoli cells secrete a protein having the same immunochemical and physical properties as clusterin isolated from ram rete testis fluid. Possible functions of clusterin are discussed.

Amino Acids↗
PubMed1983

Ram rete testis fluid contains a protein (clusterin) which influences cell-cell interactions in vitro.

Ram rete testis fluid is shown to elicit clustering of suspensions of Sertoli cells from testes of immature rats, TM-4 cells derived from mouse testis, and erythrocytes from several species. Details of bioassay procedures and characteristics of the phenomenon are reported. Concanavalin A and wheat germ agglutinin prevent aggregation elicited by rete testis fluid, and this inhibition is specifically prevented by alpha-methylmannoside and N-acetyl-glucosamine, respectively. Influences of rete testis fluid on cell aggregation are not dependent on exogenous calcium, but clustering is blocked by various metabolic inhibitors such as dinitrophenol. Rete testis fluid addition to mixed suspensions of erythrocytes and TM-4 cells is followed by separate aggregation of each cell types. Using aggregation of TM-4 cells suspended in simple medium at low density in rotation as a bioassy, we have determined which fractions in rete testis fluid retain activity. We have shown that a heat-stable, trypsin-sensitive protein, having an isoelectric point below pH 4.0, retains the capacity to aggregate cells. We discuss the possible functions of this protein, named clusterin, in cell interactions.

Animals↗