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Biomedical subjects

H L Bank

Publications and source records attributed to H L Bank.

At least 19 recordsLinked to original sources
PubMed1991

Transplantation of cryopreserved canine venous allografts.

Local vascular reconstructions frequently require the use of vein grafts to bridge arterial or venous defects. Most previous studies on the use of cryopreserved veins have used relatively large caliber vessels. There have been few studies on the effectiveness of cryopreserved micro- or small-venous allografts. Here, we tested two types of cryopreserved venous allografts: (1) 1.5- to 1.9-mm diameter microvenous grafts (MVG); and (2) 4- to 5-mm diameter small venous grafts (SVG). Cryopreserved MVG allografts were placed into saphenous arteries of six experimental dogs and SVG cryopreserved allografts were placed into femoral arteries of six experimental dogs for 3 to 6 weeks. Two fresh MVG autografts were also transplanted into experimental dogs as controls and autografts were transferred to the contralateral side in SVG dogs as controls. None of the six cryopreserved MVG grafts retained patency but three/six cryopreserved SVG allografts were patent at harvest. Histological examination of grfts revealed control autografts were undergoing arterialization with an intact intima. Experimental cryopreserved allografts showed extensive medial fibrosis, significant lymphocytic infiltrates, and sporadic areas of intact intima for both patent and nonpatent grafts.

Animals↗
PubMed1990

Bactericidal effectiveness of modulated UV light.

Studies were designed to evaluate the effectiveness of pulsed modulated UV light waveforms for killing bacteria. Exposure of five strains of bacteria to the modulated information encoded in the light decreased the colony population from a confluent lawn to less than 20 colonies. However, approximately 2,000 colonies survived treatment with the same intensity and time of exposure to UV light lacking the modulated information.

Bacteria↗
PubMed1989

Power analysis of statistical methods for comparing treatment differences from limiting dilution assays.

Six different statistical methods for comparing limiting dilution assays were evaluated, using both real data and a power analysis of simulated data. Simulated data consisted of a series of 12 dilutions for two treatment groups with 24 cultures per dilution and 1,000 independent replications of each experiment. Data within each replication were generated by Monte Carlo simulation, based on a probability model of the experiment. Analyses of the simulated data revealed that the type I error rates for the six methods differed substantially, with only likelihood ratio and Taswell's weighted mean methods approximating the nominal 5% significance level. Of the six methods, likelihood ratio and Taswell's minimum Chi-square exhibited the best power (least probability of type II errors). Taswell's weighted mean test yielded acceptable type I and type II error rates, whereas the regression method was judged unacceptable for scientific work.

Cell Survival↗
PubMed1989

Comparison of statistical methods for the analysis of limiting dilution assays.

This study reports the results of a critical comparison of five statistical methods for estimating the density of viable cells in a limiting dilution assay (LDA). Artificial data were generated using Monte Carlo simulation. The performance of each statistical method was examined with respect to the accuracy of its estimator and, most importantly, the accuracy of its associated estimated standard error (SE). The regression method was found to perform at a level that is unacceptable for scientific research, due primarily to gross underestimation of the SE. The maximum likelihood method exhibited the best overall performance. A corrected version of Taswell's weighted-mean method, which provides the best performance among all noniterative methods examined, is also presented.

Cell Survival↗
PubMed1989

Parameters for evaluation of viability assays: accuracy, precision, specificity, sensitivity, and standardization.

The selection of appropriate viability assays is critical in evaluating the efficacy of any cryopreservation procedure. The appropriateness of a given assay depends on the specific tissue and the function which is being optimized. Although a broad range of "viability" assays have been used, these assays can be classified in seven principle groups: (i) Morphological procedures, including routine histology, surface antigen localization, and transmission electron or scanning microscopy; (ii) proliferation studies; (iii) metabolic assays; (iv) implantation; (v) mechanical assays; (vi) motility; and (vii) DNA or RNA synthetic assays. Regardless of the class of assay, each assay may be further characterized as qualitative, quantitative, or quantal and each type may vary in the degree of subjectivity. In selecting a specific viability assay, biological variability, assay bias, and the statistical probability of both Type I and Type II errors should be considered crucial. Here we discuss a number of critical factors involved in validating viability assays, including accuracy, precision, standardization, specificity, sensitivity, selection of statistical methodology, and range of the assay.

Animals↗
PubMed1989

Freeze-dried microarterial replacement allografts in rabbits.

Microvascular techniques offer important alternatives for reconstructive head and neck surgery. To test the viability of freeze-dried allografts, a pilot experimental study was performed using the rabbit model. Freeze-dried preserved arterial allografts were implanted into femoral artery defects in eight subjects. After 6 weeks, all grafts were harvested and prepared for histological and electron microscopic analysis. Immediate patency was 100%. One subject was excluded on the third postoperative day. Of the seven remaining grafts, three (43%) were patent at 6 weeks. These results are comparable to previous data obtained using freeze-dried arterial allografts in the same animal model. Although further investigation is required, this pilot study suggests possible future application of cryopreserved vascular micrografts.

Animals↗
PubMed1987

Basic principles of cryobiology.

The ultimate aim of most cryopreservation procedures is the retention of the structural and functional integrity of the frozen cells or tissue. Designing strategies for achieving high "viability" of the frozen tissue requires an appreciation of the complex physical-chemical events which occur during freezing and thawing, as well as the importance of other processing steps including tissue procurement and post-thaw processing of the tissue, all of which can adversely affect the tissue. Here we have provided a general overview of cryobiology with special emphasis on techniques for organ preservation.

Cryopreservation↗
PubMed1987

Measurement of postcryopreservation viability.

For any tissue, there is a cell viability threshold below which the ability of the tissue to maintain itself and function will eventually be compromised. During cryopreservation and subsequent thawing of tissues there are many steps involved, each with attendant potential risks for reduction of viability. To determine the effectiveness of any cryopreservation procedure it is important to select appropriate assays. In this manuscript viability assays, in general, are reviewed from a biological viewpoint prior to review of methods employed for assessment of heart valve viability. Both in situ and in vitro assays of heart valve viability indicate that valve mechanical properties and the majority of fibroblasts, which are responsible for maintenance of the valve connective tissue, are retained after cryopreservation.

Cryopreservation↗
PubMed1979

Cryogenic preservation of isolated rat Islets of Langerhans: effect of cooling and warming rates.

Isolated rat Islets of Langerhans have been frozen to and stored at -196 degrees. After thawing, these islets were capable of secreting near normal levels of insulin in response to graded glucose challenge. Maximal retention of functional viability as measured by the ability of the islets to secrete insulin in response to a glucose challenge was obtained after freezing islets at a cooling rate of approximately 75 degrees per minute in the presence of 1.0 mol/1 dimethyl sulfoxol followed by warming at rates of greater than 3.5 degrees/minute. The critical freezing parameters include the time and temperature of exposure to dimethyl sulfoxide, the rate of cooling, the temperature of the post-thaw dilution from the freezing medium and the presence of serum in the dilution medium.

Animals↗
PubMed1979

X-ray microanalysis of pyroantimonate-precipitable cations.

Modifications of the Komnick potassium (pyro)antimonate precipitation method have been widely used for the subcellular localization of a variety of cations. The identity of cations precipitated with this method has often been controversial, and it is therefore important to establish definitive criteria for identifying precipitated cations in situ. In the present study, we have precipitated antimonate salts in vitro and examined the salts both in crystalline powder form and after embedment in Epon, using energy-dispersive X-ray microanalysis, in an attempt to identify biologically important antimonate-precipitable cations. We have found that the cations sodium, magnesium, and calcium, if present in physiological concentrations, will precipitate antimonate under "standard" conditions (2.5% antimonate, pH 7.2 - 7.4, in the presence of 1% OsO4). Characteristic X-ray emissions were observed for sodium and magnesium, as well as for lead similarly precipitated, but Lalpha and Lbeta emission peaks from antimony interfered with calcium identification and necessitated complex computerized deconvolution or peak stripping to determine the presence of a calcium peak. Precipitates of sodium did not contain appreciable potassium, whereas variable amounts of potassium were present in precipitates of calcium and lead, depending upon the extent of washing prior to dehydration. Sizeable potassium peaks were consistently present in even well washed magnesium precipitates. X-ray spectra of standardized precipitates were found useful as an aid in interpreting the more complicated spectra obtained from tissue samples.

Animals↗
PubMed1978

Phagocytosis of bacteria by polymorphonuclear leukocytes. A freeze-fracture, scanning electron microscope, and thin-section investigation of membrane structure.

The changes in membrane structure of rabbit polymorphonuclear (PMN) leukocytes during bacterial phagocytosis was investigated with scanning electron microscope (SEM), thin-section, and freeze-fracture techniques. SEM observations of bacterial attachment sites showed the involvement of limited areas of PMN membrane surface (0.01-0.25mum(2)). Frequently, these areas of attachment were located on membrane extensions. The membrane extensions were present before, during, and after the engulfment of bacteria, but were diminished in size after bacterial engulfment. In general, the results obtained with SEM and thin-section techniques aided in the interpretation of the three-dimensional freeze-fracture replicas. Freeze-fracture results revealed the PMN leukocytes had two fracture faces as determined by the relative density of intramembranous particles (IMP). Membranous extensions of the plasma membrane, lysosomes, and phagocytic vacuoles contained IMP's with a distribution and density similar to those of the plasma membrane. During phagocytosis, IMPs within the plasma membrane did not undergo a massive aggregation. In fact, structural changes within the membranes were infrequent and localized to regions such as the attachment sites of bacteria, the fusion sites on the plasma membrane, and small scale changes in the phagocytic vacuole membrane during membrane fusion. During the formation of the phagocytic vacuole, the IMPs of the plasma membrane appeared to move in with the lipid bilayer while maintaining a distribution and density of IMPs similar to those of the plasma membranes. Occasionally, IMPs were aligned to linear arrays within phagocytic vacuole membranes. This alignment might be due to an interaction with linearly arranged motile structures on the side of the phagocytic vacuole membranes. IMP-free regions were observed after fusion of lysosomes with the phagocytic vacuoles or plasma membrane. These IMP-free areas probably represent sites where membrane fusion occurred between lysosomal membrane and phagocytic vacuole membrane or plasma membrane. Highly symmetrical patterns of IMPs were not observed during lysosomal membrane fusion.

Animals↗
PubMed1978

Intramembranous particles in erythrocyte, reticulocyte and erythroblastic leukemic cells of the rat: a model system for erythrocyte maturation.

The density and size distribution of intramembranous particles (IMP) were determined for cells of the erythroid series. The number and size of IMP were measured on both fracture faces of erythroblastic leukemia cells, phenylhydrazine-induced reticulocytes and mature erythrocytes. We found that the number of IMP adhering to the protoplasmic fracture face of the plasma membrane increased with increasing maturation, while the number of particles adhering to the external fracture face did not correlate with maturational stage. In general, the mean size of particles adhering to both fracture faces decreased with increasing maturation after the erythroblastic stage. We interpret these results to mean that the IMP seen are derived from more than one macromolecular species and that they are distributed asymmetrically in the plasma membrane.

Animals↗
PubMed1978

Human marrow erythropoiesis in culture: III. Ultrastructural and cytochemical studies of cellular interactions.

Human erythroblasts cultured with a methylcellulose clonal assay technique were studied with ultrastructural and cytochemical methods. The intact colonies contained only erythroblasts at a similar stage of maturation, and no macrophages were identified within the colonies. The cultured erythroblasts demonstrated many of the morphologic features described in vivo. Neutral and acid glycoconjugates identified on the plasmalemma stained in a similar way to that seen in vivo with a concanavalin A horseradish peroxidase bridge and dialyzed iron technique. Weak acid phosphatase activity and ferritin-like particles were demonstrated in siderosomes, but these structures lacked peroxidase activity and dialyzed iron reactive acid mucosubstance. Transmission and scanning electron microscopy identified numerous processes which connected early erythroblasts and resembled those described in the marrow of patients with dyserythropoietic disorders. These findings suggest the presence of abnormalities in cultured erythrocytes which should be considered when evaluating pathologic specimens in vitro.

Bone Marrow Cells↗
PubMed1977

Granule release by polymorphonuclear leukocytes treated with the ionophore A23187.

Polymorphonuclear leukocytes (PMN's) incubate three to eight minutes at 37 degrees C in medium containing 1 X 10(-6) M of the ionophore antibiotic A23187 released their cytoplasmic granules into the extracellular medium. Transmission electron microscopy of treated cells showed microfilament bundles extending between adjacent granules within the cytoplasm and between granules and the plasma membrane. Tiny dense projections (beads) 8-12 nm in diameter were observed along segments of the cytoplasmic surface of the plasma membrane with a periodicity of 20-30 nm. These beads were observed on the plasma membrane only in the vicinity of intra- or extracytoplasmic granules. The structural relationships of the beads with the plasma membrane microfilaments suggest they play a role in the process of ionophore-induced granule release from polymorphonuclear leukocytes.

Animals↗