The longevity of chick tissue cultures without renewal of medium

Prediction of subcutaneous drug absorption - do we have reliable data to design a simulated interstitial fluid?

For many years subcutaneous (SC) administration has represented the main route for delivering biopharmaceuticals. However, little information exists about the milieu in the subcutaneous tissue, especially about the properties/composition of the fluid present in this tissue, the interstitial fluid (ISF), which is one of the key elements for the drug release and absorption. Better knowledge on SC ISF composition, properties and dynamics may provide better insight into in vivo drug performance. In addition, a simulated SC ISF, which allows better prediction of in vivo absorption of drugs after subcutaneous administration based on in vitro release experiments, would help to improve formulation design, and reduce the number of animal studies and clinical trials required to obtain marketing authorization. To date, a universal medium for predicting drug solubility/release in the interstitial space does not exist. This review provides an overview of the currently available information on composition and physicochemical properties of SC ISF and critically discusses different isolation techniques in the context of information that could be gained from the isolated fluid. Moreover, it surveys current in vitro release media aiming to mimic SC ISF composition and highlights information gaps that need to be filled for designing a meaningful artificial SC ISF.

The use of physiological solutions or media in calcium phosphate synthesis and processing

This review examined the literature to spot uses, if any, of physiological solutions/media for the in situ synthesis of calcium phosphates (CaP) under processing conditions (i.e. temperature, pH, concentration of inorganic ions present in media) mimicking those prevalent in the human hard tissue environments. There happens to be a variety of aqueous solutions or media developed for different purposes; sometimes they have been named as physiological saline, isotonic solution, cell culture solution, metastable CaP solution, supersaturated calcification solution, simulated body fluid or even dialysate solution (for dialysis patients). Most of the time such solutions were not used as the aqueous medium to perform the biomimetic synthesis of calcium phosphates, and their use was usually limited to the in vitro testing of synthetic biomaterials. This review illustrates that only a limited number of research studies used physiological solutions or media such as Earle's balanced salt solution, Bachra et al. solutions or Tris-buffered simulated body fluid solution containing 27mM HCO3(-) for synthesizing CaP, and these studies have consistently reported the formation of X-ray-amorphous CaP nanopowders instead of Ap-CaP or stoichiometric hydroxyapatite (HA, Ca10(PO4)6(OH)2) at 37°C and pH 7.4. By relying on the published articles, this review highlights the significance of the use of aqueous solutions containing 0.8-1.5 mMMg(2+), 22-27mM HCO3(-), 142-145mM Na(+), 5-5.8mM K(+), 103-133mM Cl(-), 1.8-3.75mM Ca(2+), and 0.8-1.67mM HPO4(2-), which essentially mimic the composition and the overall ionic strength of the human extracellular fluid (ECF), in forming the nanospheres of X-ray-amorphous CaP.

Characterization of a potential medium for ‘biorelevant’ in vitro release testing of a naltrexone implant, employing a validated stability-indicating HPLC method

A variety of factors have been recognized that influence media optimization for drug release studies of implant dosage forms. Of primary importance is selection of a medium that physiologically mimics the milieu at the site of administration (a condition termed 'biorelevance'). We describe in this paper, the characterization of Hanks' balanced salts solution, with necessary modification, for application as a 'biorelevant' medium for in vitro release studies of a biodegradable, subcutaneous implant of naltrexone. A detailed investigation of changes in pH, osmolality and ultraviolet (UV) spectrum as a function of time and temperature was conducted. Variation in the parameters evaluated was found to be within acceptable limits. Validation of a simple and selective, high performance liquid chromatography (HPLC) assay method for naltrexone was carried out to evaluate stability. The calibration curves were linear from 0.16 to 20.00 microg ml(-1). Imprecision and inaccuracy were less than 2% and no interference was observed from degradation peaks. Stability studies of naltrexone indicated the media should be replaced every 7-8 days for real-time testing. This was applied to an investigation of in vitro drug release. The method has been proven to be suitable for investigation of naltrexone released from the implant.

[Biochemical characterization of calf sera used in the maintenance of cell cultures used in virology]

Eight lots of the calf sera employed to supplement culture media for the cultivation of animal cells, of widespread use in virology obtained from calves above and below six months of age were rated as good or as poor cell growth promoters according to their growth promoting capacity (GPC). Parameters related to macronutrients contained in these serum lots were then evaluated with the purpose of establishing their biochemical profiles. The results obtained can be considered as normal values for apparently healthy animal donors. Fluctuations found between the data of this investigation and those mentioned in the literature for certain biochemical parameters are probably due to the methodology employed, the breed and age of the animals, or even to regional diet. Student's "t" test was applied for the statistical analysis of the results and demonstrated that, as far as serum fractions were concerned, no significant differences occurred between sera rated as good and poor cell growth promoters, taking tc = 2.45. For calf sera from animals above and below six months of age, two tests relating to alfa and beta fractions were significant (t = 2.68 and 2.61 respectively). It was demonstrated that the evaluation of the biochemical parameters mentioned "per se" neither leads to the identification of calf sera presenting good or poor GPC, nor of sera harvested from calves younger or older than six months.

A combined in ovo-in vitro system for studies of volatile compounds on brain development: differential effects of carbon tetrachloride on neurones and astrocytes

A method for studies of organic solvent effects on the development of neurones and astrocytes is described. Chick embryos in ovo were exposed to a low concentration of carbon tetrachloride vapours. After the exposure, primary cultures of neurones and astrocytes were prepared from the brain hemispheres of the embryos. Toxic effects of the solvent were analyzed in the cultures during the course of cellular differentiation as changes in cell growth and morphology, respiratory activity, and biochemical properties characteristic of each cell type. The development of neurones from embryos exposed from day 5 to day 8 to 25 p.p.m. of carbon tetrachloride was not affected by the exposure. On the other hand, growth rate and respiratory activity of astrocytes from embryos exposed from day 11 to day 14 to 25 p.p.m. of CCl4 were affected by the exposure, whereas no morphological changes or changes in the cyclic AMP levels could be observed. Consequently, low concentrations of carbon tetrachloride seem to affect the development of astrocytes rather than that of neurones in our experimental system.

Effects of temporary cooling, and of different explantation and storage conditions, on the subsequent development of post-implantation rat embryos in vitro

Rat embryos explanted at head fold stage were stored under various levels of hypothermia prior to culture. The storage media were Hanks' Balanced Salt Solution (BSS), 50% rat serum with 50% Dulbecco's Modification of Eagle's Medium (standard medium), or 100% rat serum. The media were gassed with 5% O2/5% CO2/90% N2 or 20% O2/5% CO2/75% N2. Subsequent development of embryos after storage at temperatures between 10 degrees C and 30 degrees C for 5 hr in Hanks' BSS, or for 5-10 hr in standard medium or serum, was similar to that of controls. Some embryos developed well even after storage for 48 hr in standard medium. Development was poorer after storage at 0 degrees C or 5 degrees C, and after storage at all temperatures in ungassed Hanks' or standard medium (pH greater than 8.0). Differences in oxygen level had little effect. For routine explantation at room temperature in (ungassed) phosphate-buffered saline solutions such as Hanks', it is recommended that the delay before transferring the embryos to the culture incubator not exceed 2-3 hr.

Differential effect of zinc on teratogen-induced inhibition of pinocytosis by cultured rat yolk sac

Pinocytosis as measured by the uptake of 125I labelled PVP by the isolated cultured day 12 rat yolk sac was observed to be linear over a 4 h incubation period and to proceed at a rate of approximately 2.5 microliters/mg protein/h. Cadmium, anti-visceral yolk sac antibody (AVYS) and trypan blue all inhibited pinocytosis in a concentration-dependent fashion when added to the culture medium, although at low concentrations trypan blue was slightly stimulatory. The effect of zinc on the inhibition of pinocytosis by these three teratogens was studied. It was observed that zinc ameliorated the inhibitory effects of cadmium and AVYS, but had no effect on inhibition by trypan blue. These results indicate that the previously demonstrated protective action of zinc against cadmium-induced yolk sac dysfunction is not specific to that agent but extends to inhibition of pinocytosis by AVYS, and further suggest that, because of its refractoriness to zinc, trypan blue-induced inhibition of pinocytosis by yolk sac occurs by a mechanism different from that effected by cadmium and AVYS.

Evidence for an early degradative event to the insulin molecule following binding to hepatocyte receptors

We have used photoreactive insulin analogues to investigate as related processes, early structural modification of the receptor-bound insulin molecule and internalisation of the insulin-receptor complex. In isolated rat hepatocytes an initial modification of bound insulin leads to the generation of a molecular species unchanged in molecular weight but with reduced receptor and antibody binding affinities and altered electrophoretic mobility. Using photoreactive insulin analogues and density gradient cell fractionation the insulin receptor complex has been shown to undergo internalisation from the plasma membrane to a low density vesicular fraction, the endosome. No labelled material was found in lysosomal fractions after up to 10 min incubation at 37 degrees C. The degree of labelling of the endosome fraction depended on the position of the photoreactive group within the insulin molecule. The data suggest that before or during endocytosis, a small peptide is proteolytically cleaved from the C terminus of the insulin B chain.

Factors controlling the DNA-synthesis in 3T3 and EAT cells

Beta globulins, (Cohn Fr. III), are a major source of molecules affecting the DNA-synthesis of 3T3 and EAT cells. Growth inhibitors for both cell types, chromatograph at the same position, corresponding to a mol. wt of about 50,000. A very basic, (pI 10.1), factor is isolated by gel electrofocusing, which stimulates the DNA-synthesis of 3T3 and EAT cells. Because of its extremely high cationic charge and its adsorption on gels, the estimation of the exact molecular weight and its preparative isolation, becomes very difficult. Some of the above mentioned molecules are heat-stable and express their action even after boiling for 10 min at pH 3.

Similarities between the Mr 245,000 calmodulin-binding protein of the dogfish erythrocyte cytoskeleton and alpha-fodrin

The Mr 245,000 calmodulin-binding protein of the dogfish erythrocyte cytoskeleton (D245) has been compared with human erythrocyte spectrin and mammalian brain fodrin [J. Levine and M. Willard (1981) J. Cell Biol. 90, 631-643]. Mammalian erythrocyte alpha-spectrin, brain alpha-fodrin, and D245 are all localized in the cell surface-associated cytoskeleton, and have similar molecular weights. Like mammalian erythrocyte spectrin, D245 was extracted from erythrocyte ghosts under low-ionic-strength conditions. However, D245 failed to bind an antibody which reacted strongly with both subunits of human erythrocyte spectrin. Unlike mammalian erythrocyte alpha- and beta-spectrin, D245 bound calmodulin in the absence of urea both in a "gel-binding" assay and in situ using azidocalmodulin [D.C. Bartelt, R.K. Carlin, G.A. Scheele, and W.D. Cohen (1982) J. Cell Biol. 95, 278-284]. Striking similarities were noted between D245 and alpha-fodrin in that both exhibited (a) comparable calcium-dependent calmodulin binding properties, (b) strong reactivity with two different anti-fodrin antibody preparations, (c) similar reactivity with antibody to brain CBP-I, now believed to be fodrin, (d) proteolytic degradation yielding an Mr 150,000 calmodulin-binding fragment, and (e) lack of reactivity with an anti-spectrin antibody. A protein with calmodulin-binding and anti-fodrin-binding properties similar to D245 was detected in cytoskeletal preparations of chicken erythrocytes. Moderate and consistent cross-reactivity of anti-fodrin with human erythrocyte alpha-spectrin was also observed. The data indicate that D245 is functionally and immunologically more closely related to alpha-fodrin than to alpha-spectrin of the mammalian erythrocyte.

Disinfection of human heart valve allografts with antibiotics in low concentration

Antibiotic disinfection of allograft heart valves is now an established procedure. A new low-concentration, broad-spectrum mixture of antibiotics was formulated and used successfully to disinfect 58 of 60 human aortic and pulmonary valves after 48 h exposure at 4 degrees C. The antibiotics included were cefoxitin 240 mcg/ml, lincomycin 120 mcg/ml, polymyxin B 100 mcg/ml, vancomycin 50 mcg/ml and amphotericin B 25 mcg/ml. Microorganisms isolated from experimental tissue and from clinical valves before treatment were tested for sensitivity to these antibiotics and were found to be sensitive to one or more. One isolate of Pseudomonas spp. showed decreased sensitivity to polymyxin B, and was found to have a minimum bactericidal concentration of 70 mcg/ml. Results indicated this antibiotic mixture had superior antibacterial efficiency to that in routine clinical use for the past 13 yr.

Variation in composition of media and reagents used in the preparation of cell cultures from human and other animal tissues: Dulbecco's, Earle's, and Hanks' balanced salt solutions

When comparison was made of directions given for three salt solutions commonly used in cell culture preparations and identified as Dulbecco's, Earle's, and Hanks', variations in composition were found. Some significantly alter the suitability of the materials for the intended use. Other differences may have less effect. This brief review reveals a tendency among researchers to follow procedures obtained from colleagues for the preparation of laboratory reagents and media, to cite the original publication rather than their colleagues' work as the source of the information, and to fail to compare the two for differences. Some failures in cell culture propagation may be attributed to similar instances with other published but incorrectly cited work. Tables are provided that facilitate comparison of the correct original formulations with variants from selected published sources.

Purification of detergent-extracted Sendai virus proteins by reversed-phase high-performance liquid chromatography

Sendai virus envelope proteins were isolated by reversed-phase high-performance liquid chromatography. The F (F1 and F2, connected by disulphide bonds), M and HN proteins were extracted from purified Sendai virions with Triton X-100. After removal of the detergent from the extract with Amberlite XAD-2 and reduction of the proteins, separation was performed on a small (10-nm) and on a larger (30-nm) pore size C18 column. Proteins were eluted with a gradient of an ethanol 1-butanol mixture in 12 mM hydrochloric acid. On the 10-nm pore size column, F2 was completely recovered in pure form, whereas the recoveries of the other proteins were low (5-25%). Similar results were obtained with the 30-nm pore size column, except for protein F1 of which the yield was higher (50%).

The surface glycoproteins of human skin fibroblasts detected after electrophoresis by the binding of peanut (Arachis hypogaea) agglutinin and Ricinus communis (castor-bean) agglutinin I

A new methodology was developed to study the cell-surface glycoproteins of cultured human skin fibroblasts. This was based on the binding of a variety of biotinyl-lectins to nitrocellulose electrophoretic transfers of total fibroblast lysates after separation in sodium dodecyl sulphate/polyacrylamide gels, followed by reaction with avidin-biotinyl-peroxidase complexes and detection with 3,3'-diaminobenzidine. The technique proved to be very sensitive and a large number of glycoproteins were detected by binding of concanavalin A and wheat-germ agglutinin. Binding of peanut agglutinin and to a lesser extent of Ricinus communis agglutinin I were found to be dependent on prior removal of sialic acid residues from the glycoproteins. Since by treatment of intact viable cells with neuraminidase only external sialic acid residues were removed, peanut agglutinin and Ricinus communis agglutinin I could thus be utilized for selective detection of cell-surface glycoproteins. Also, because peanut agglutinin was known to bind preferentially to oligosaccharides of the O-glycosidic type, and Ricinus communis agglutinin I to those of the N-glycosidic type, the two lectins were complementary in displaying the surface glycoproteins and in providing information about their oligosaccharide composition.

Different response of liver parenchymal cells from starved and fed rats to cadmium

The susceptibility of hepatocytes to the deleterious effects of cadmium (10-100 microM Cd), as evidenced by SH-group content and cell membrane permeability for Trypan Blue (TB), was shown to be strongly dependent on the dietary condition of the donor animal. Although Cd stimulated lipid peroxidation (LPO) equally well in "starved" as in "fed cells", SH-group content and TB-exclusion decreased markedly only in "starved" cells exposed to Cd. Experiments with methionine + serine and/or the antioxidant (+)-cyanidanol-3 suggested that the Cd-dependent LPO proceeded independent of the decrease in SH-group content or TB-exclusion.

Persistence of colchicine resistance in Ehrlich-Lettré ascites tumors and cell strains

The effect of colchicine on mitoses of mutant HD33 Ehrlich-Lettŕe ascites cells growing in vivo and in vitro was studied. HD33 mouse ascites tumors are colchicine-resistant. The LD50 of colchicine in mice bearing HD33 ascites tumors was 1.4 mg/kg body weight (b.w.), but a single dose of 3.33 mg colchicine/kg b.w. failed to suppress the anaphase of HD33 tumor mitoses for 24 h. No change in the level of colchicine resistance was observed after 269 weekly transplantations of HD33 ascites tumors without colchicine. In suspension culture, growth of HD33 ascites cells ceased at 1.5 x 10(-6) M colchicine. 10(-5) M colchicine suppressed the anaphase of HD33 mitoses and produced typical C-mitoses within one hour. The same effects on mitoses of colchicine sensitive Ehrlich ascites cells in vitro were achieved with 10(-6) M colchicine. In HD33 ascites cell cultures grown without colchicine, only a slight increase in colchicine sensitivity was registered after 5 years. Parallel cultures were propagated for the same period in the presence of 10(-7) M colchicine (HD33C ascites cells) without detectable growth alterations; the resistance level increased slightly. The limit of 10(-6) M colchicine was tolerated by the ascites cells in permanent culture without growth reduction (HD33CS ascites cells). 3H-colchicine binding studies suggest a permeability barrier of the plasma membrane as a mechanism of genetically fixed resistance.

Decreased tumorigenicity of rodent cells after fusion with leukocytes from normal and leukemic donors

Interspecific hybrid cells, derived from fusion of normal and leukemic (CML) human leukocytes with tumorigenic P19 mouse or a3 Chinese hamster cells, were tested for their tumor-forming capacity in congenitally athymic nude mice. Partial suppression of tumorigenicity was observed in several hybrid clones derived from both normal and leukemic leukocytes. Chromosome analysis of the hybrid cells before inoculation in nude mice and of the derived tumors did not reveal a human chromosome bearing factor(s) which singly appeared responsible for suppression. The presence of the Philadelphia translocation in the leukemic cells does not seem to have deprived these cells of their tumor-suppressing ability.

The effect of bezofibrate and clofibrate on cholesterol accumulation, esterification and removal in cultured 3T3 fibroblasts

3T3 mouse fibroblasts were used to determine the effect of bezafibrate and clofibrate on the cellular metabolism of cholesterol. In cells incubated in normal medium these agents decreased the incorporation of 3H-labelled oleic acid relative to 14C-labelled linoleic acid into the cholesterol ester fraction. When the 3T3 fibroblasts were incubated with cationised low density lipoprotein (LDL) the amount of esterified cholesterol which accumulated in the cells was greatly increased. This accumulation of cholesterol ester was reduced by bezafibrate and clofibrate. These agents decreased the incorporation of both 3H-labelled oleic acid and 14C-labelled linoleic acid into the cholesterol ester fraction of the cells, with a preferential effect on oleic acid as indicated by a reduction in the 3H/14C ratio. When cells which had been preincubated with cationised LDL were reincubated in normal medium, the removal of esterified cholesterol from the cells was increased by both bezafibrate and clofibrate. The mechanism of the effects of these agents on the metabolism of cellular cholesterol is discussed.

Increasing human serum ribonuclease activity is a concomitant phenomenon of ovarian carcinoma

The levels of total human serum RNAase activity (HSRA) from 24 patients with ovarian cancer have been followed up for a period of over 5 months. The determinations of HSRA were carried out according to our assay system described earlier. Two representative patterns of the HSRA are presented, one from a patient with an ascertained remission of an ovarian carcinoma. Increasing HSRA values are concomitant with tumor progression while in remission the HSRA remains at normal rates. We have reported earlier that optimum HSRA depends on physiological concentrations of NaCl in the reaction mixture. However, NaCl can be replaced by KCl without a loss of activity. No correlation was detectable between increased HSRA and an excessive electrolyte content in serum. The mixtures of sera with various RNAase activities showed linear additivity. These findings suggest that an increased concentration of the RNAases normally present in human serum and/or additional RNAases are responsible for the increase of the HSRA.

Spike potentials and membrane properties of dorsal root ganglion cells in pigeons

Active and passive membrane properties of dorsal root ganglion (DRG)-cells from the intact superfused ganglion of pigeons have been compared with the conduction velocity of their centrifugal axons. About two thirds of the neurones were associated with myelinated axons and classified as A-cells; the remainder were associated with unmyelinated axons and classified as C-cells. Slowly conducting group III A-cells (5--25 m . s-1) constituted half of the A-cell population. With exception of spike duration, spike parameters and membrane properties did not differ among the A-cells. Spike duration increased with decreasing conduction velocity demonstrating a small plateau ("hump") during the fall time in group III neurones. This hump was more distinct in C-cells, resulting in a 2--5 times longer duration of action potentials. Amplitude and duration of afterhyperpolarization (AHP) of C-cells was 2--3 times that of A-cells. Administration of 10 mM CoCl2 decreased the rate of rise and the overshoot but increased the rate of fall of the action potential in C-cells and group III A-cells, largely abolishing the hump. It is suggested that the hump of the spike potential is largely produced by a Ca-current and that the resultant increase of intracellular Ca might produce the larger AHP in C-cells, secondary to an increase in K-conductance.

Loss of differentiation features in trypsin separated heart muscle cells

Loss of maturation features is demonstrated for 8-day-old chick embryo heart myocytes, once they have been completely dissociated by trypsin. In support of this statement a total of 65 sections of six isolated cells, fixed while still spherical or during early flattening, were examined under the electron microscope. Trypsin-separated heart muscle cells, even though originating from already differentiated embryonic heart tissue, can therefore in principle be used for differentiation experiments in culture. However, the same cell suspensions also yielded an appreciable quantity of nonisolated cells. In such cell complexes, one can find areas showing well-ordered fibrils and intercalated disks. From 27 sections of a cell pair incidentally transferred into culture undissociated and then fixed while still in the globular state, the fourth and fifth sections, starting from the substrate side of the culture, showed an intercalated disk. Because of its small diameter, this cell complex would hardly have been retainable by a gauze with meshes likely to allow passage of only single cells. Thus the availability of differentiation experiments in culture, starting with already differentiated heart tissue, is restricted to cases where, in a selected territory, each cell has been established without doubt as isolated.

Effects of low tissue temperature on peripheral vascular control mechanisms

Influence of low temperatures on vascular effects produced adrenaline, noradrenaline and vasoconstrictor nerve stimulation was studied in the feet of ducks. Observations were made on isolated preparations as well as on intact ducks with one or both feet immersed in ice-water. Isolated preparations were perfused with physiological solution and information on changes in vascular resistance obtained by direct measurement of flow changes during perfusion at constant pressure or by measuring changes in perfusion pressure during perfusion at constant flow. In intact ducks changes in blood flow were recorded as changes in digital subcutaneous tissue temperature. The study revealed that in the duck foot a relatively large fraction of the resistance to blood flow is found in the arteries of the proximal part of the foot. During cooling of the foot the influence of vasoconstrictor nerve stimulation and low doses of adrenaline and noradrenaline on vascular resistance is gradually lost, and it is negligible at temperatures below 8 degrees C. At these low temperatures the blood vessels stay dilated and blood flow through the web seems to be determined by the digital arterial blood pressure.

A mechanical momentum in ultrastructural development of the heart

The question of whether mechanical moments participate in ultrastructural development of the heart cannot be decided by examining heart tissue samples during embryonic life, for during maturation processes in vivo mechanical factors are always present. The significance of mechanical moments can only be investigated in a system which allows a distinction to be made between pulsations of heart myocytes under conditions of contraction against and under conditions of contraction without mechanical stress. This double possibility is provided by cell culture. An example in which mechanical influences are absent are the so-called "minihearts"; these are cell agglomerations which are detached from the culture substrate. Their cell contractions do not act against any mechanical resistance. In the electron microscope they show abundant filaments, Z-line material and membrane specializations. The highest degree of development, however, does not exceed that characterizing the cells with which the cultures were started. Even some dedifferentiation and degeneration are apparent in the minihearts. No intercalated discs can be found even after 12 weeks, provided that the culture had been started with really isolated cells. The representatives in culture of a myocyte's connection with the heart's mechanical action are the cords, along which attached points alternate with free strands. The pulsation of these strands is restrained during each contraction by their ends, which are fixed on the culture substrate. Thus, the myocytes contract against a resistance, and in this respect their pulsations resemble those of the heart, in which the myocytes' contraction acts against the pressure of the blood. The myocyte culture under these mechanical condition, after a culture time of 10 weeks, produces electron micrographs of mature cells with reduced cytoplasm, aligned mitochondria and fibrils and intercalated discs.

The fusion of erythrocytes by treatment with proteolytic enzymes and polyethylene glycol

Polyethylene glycol (PEG) has been utilized to induce homokaryocyte formation in avian and mammalian erythrocytes previously treated with proteolytic enzymes. PEG of molecular weight 6,000-7,5000 was found superior to 1,500 and 20,000 MW PEG. Cells exposed to protease alone, prior to PEG treatment, fused to a high degree (60-95% multinucleated cells), whereas trypsin or pepsin treatment alone allowed very little fusion (2.5%). Trypsin lowered the effectiveness of protease when used in combination. Cells which were not treated with proteolytic enzymes agglutinated in the presence of PEG but did not fuse to a significant extent (0.01%). Fusion was also markedly dependent upon the rate at which PEG was eluted during the fusion process. Electron microscopy indicated that fusion began during the elution of PEG from the agglutinated cells.

Uptake of sorbitol by chick embryo heart cells at various stages of development

Sorbitol enters chick embryo heart cells from five days of development on. The rate of sorbitol entry becomes slower as development proceeds and the data suggest this is principally due to an increase in the apparent Km of transport, the Vmax remaining relatively constant. The uptake of sorbitol displays saturation kinetics and is believed on this ground to be carrier-mediated. Sorbitol does not appear to be actively transported since it is not concentrated against a gradient and its uptake is not inhibited by iodoacetate or 2, 4-dinitrophenol. Sorbitol does not appear to be taken up via the glucose transport system since uptake is not stimulated by insulin or inhibited by glucose or phloretin.

Freeze-drying from tertiary butanol in the preparation of endocardium for scanning electron microscopy

The scanning electron microscope appearances and shrinkage of blocks of canine endocardium prepared by freeze-drying directly, by freeze-drying after replacing tissue water with tertiary butanol (2-methyl propan-2-ol) and by critical point drying were compared. All three methods demonstrated endothelial cells which showed nuclear prominences, microvilli and intercellular boundaries. The microvilli varied in size and number from dog to dog but were generally less well defined in specimens freeze-dried from water. Shrinkage due to t-butanol dehydration was significantly less than that which occurred in ethanol in the critical point drying method. Overall the reduction in surface area was significantly less in specimens freeze-dried directly at -65 C (6.8%) than in those dried from t-butanol at -20 C (15.4%) and those prepared bly critical point drying (22.1%). However the amount of shrinkage observed in t-butanol treated tissue was not significantly different from that which was critical point dried. It was not possible to distinguish between comparable samples prepared by these two methods on the basis of their scanning electron microscopic appearances. Thus the relative simplicity and convenience of the t-butanol method, together with its saving of time, its use of standard freeze-drying equipment and the avoidance of ice-crystal artefact justify its consideration as an alternative method of preparing wet biological tissue for scanning electron microscopy.

A method for evaluating the effects of allograft sterilization procedures on the viability of human fibroblasts

Chalcroft, S. C. W., Gavin, J. B., and Seelye, R. N. (1974).Thorax, 29, 539-544. A method for evaluating the effects of allograft sterilization procedures on the viability of human fibroblasts. A semiquantitative method for assessing the effects of allograft sterilization procedures on the viability of cultured human fibroblasts is described. The proportions of `viable', `altered', and `non-viable' cells in four groups of fibroblasts on coverslips were estimated using light microscopy and their staining reactions with neutral red and nigrosin. While a control group of fibroblasts remained viable, exposure for one to three weeks to each of three solutions used in allograft preparation produced a progressive transition first to the altered and then to the non-viable category. These findings were confirmed by electron microscopic examination of similarly treated cells grown on millipore filters. Applications of the method are discussed.