Secretion of chondroitin SO4 by monolayer cultures of chick embryo chondrocytes

Monolayer cultures of chick embryo tibial chondrocytes incorporate 35SO42- into chondroitin SO4 which is rapidly secreted from the cells into two extracellular pools. Part of the extracellular chondroitin SO4 is recovered in a soluble form in the culture medium, and the remainder is associated with the cell matrix from which it is released by isotonic trypsinization. At 38 degrees C labeled chondroitin SO4 appears in the cell matrix fraction within 5 min after addition of 35SO42- and in the culture medium fraction 15 min after 35SO42- is added. The intracellular pool of labeled chondroitin SO4 reaches a steady state level of 150 to 200 pmol of bound SO4 per 10(6) cells in 60 min, while the cell matrix and medium fractions increase at rates of 3 and 1 nmol of bound SO4 per h per 10(6) cells, respectively. After 4 h of labeling, less than 20% of the newly synthesized cell-associated chondroitin SO4 is in the intracellular fraction. By labeling cells for 15 min at 25 degrees C 80% of the cell-associated chondroitin 35SO4 is obtained in the intracellular fraction. This material is chased without lag into both the cell matrix fraction and the medium fraction. A mixture of NaF and NaCN, both at 30 mM, lowers the cellular ATP level to 15% of normal and blocks secretion of the intracellular chondroitin SO4 into both extracellular fractions. Colchicine at 10(-6) M gives a partial inhibition of both synthesis and secretion of chondroitinSO4. Sucrose density gradient sedimentation analysis of the intracellular chondroitin SO4 and the two extracellular fractions shows that all three fractions contain both a heavy and light proteoglycan fraction. The intracellular light proteoglycan fraction is secreted preferentially into the culture medium where it represents 30% of the total culture medium pool. The ratio of 6-sulfated GalNAc to 4-sulfated GalNAc in the heavy proteochondroitin SO4 fraction is approximately twice that found for the light fraction.     

Dissociation of intracellular lysosomal rupture from the cell death caused by silica

The relationship between intracellular lysosomal rupture and cell death caused by silica was studied in P388d(1) macrophages. After 3 h of exposure to 150 μg silica in medium containing 1.8 mM Ca(2+), 60 percent of the cells were unable to exclude trypan blue. In the absence of extracellular Ca(2+), however, all of the cells remained viable. Phagocytosis of silica particles occurred to the same extent in the presence or absence of Ca(2+). The percentage of P388D(1) cells killed by silica depended on the dose and the concentration of Ca(2+) in the medium. Intracellular lyosomal rupture after exposure to silica was measured by acridine orange fluorescence or histochemical assay of horseradish peroxidase. With either assay, 60 percent of the cells exposed to 150 μg silica for 3 h in the presence of Ca(2+) showed intracellular lysosomal rupture, was not associated with measureable degradation of total DNA, RNA, protein, or phospholipids or accelerated turnover of exogenous horseradish peroxidase. Pretreatment with promethazine (20 μg/ml) protected 80 percent of P388D(1) macrophages against silica toxicity although lysosomal rupture occurred in 60-70 percent of the cells. Intracellular lysosomal rupture was prevented in 80 percent of the cells by pretreatment with indomethacin (5 x 10(-5)M), yet 40-50 percent of the cells died after 3 h of exposure to 150 μg silica in 1.8 mM extracellular Ca(2+). The calcium ionophore A23187 also caused intracellular lysosomal rupture in 90-98 percent of the cells treated for 1 h in either the presence or absence of extracellular Ca(2+). With the addition of 1.8 mM Ca(2+), 80 percent of the cells was killed after 3 h, whereas all of the cells remained viable in the absence of Ca(2+). These experiments suggest that intracellular lysosomal rupture is not causally related to the cell death cause by silica or {"type":"entrez-nucleotide","attrs":{"text":"A23187","term_id":"833253","term_text":"A23187"}}A23187. Cell death is dependent on extracellular Ca(2+) and may be mediated by an influx of these ions across the plasma membrane permeability barrier damaged directly by exposure to these toxins.     

Chondroitin SO4 catabolism in chick embryo chondrocytes

An enzyme preparation from cultured chick embryo vertebral chondrocytes attacks chondroitin SO4 oligosaccharides from the nonreducing terminal in a recycling pathway involving the sequential action of a beta-glucuronidase, a 4- or a 6-sulfatase, and a beta-N-acetylgalactosaminidase. The sequence is blocked by saccharo-1,4-lactone, an inhibitor of the beta-glucuronidase, or by 2-acetamido-2-deoxy-D-galactonolactone, an inhibitor of the beta-N-acetylgalactosaminidase. The level of 4-sulfatase activity is low relative to the other activities and limits the rate of catabolism of hybrid oligosaccharide structures containing both 6-sulfated galactosamine residues and 4-sulfated galactosamine residues. This results in the accumulation of shortened oligosaccharides, most of which have galactosamine-4-SO4 residues at their nonreducing terminals. In the presence of the lactone inhibitors, polymeric chondroitin SO4 is broken down by the enzyme preparation to oligosaccharides which are 10 to 15 monosaccharides long, indicating that degradation of chondroitin SO4 chains is initiated by an endoglycosidase which generates oligosaccharide substrates for the recycling exoglycosidase system.     

COMPLETE ATRIOVENTRICULAR CANAL AND COR TRIATRIATUM

Two patients with complete atrioventricular canal and coexisting cor triatriatum are described. This rare combination of defects probably results from nonrelated embryological events. Successful correction was limited by the major lesion, complete atrioventricular canal, due to inadequate reconstruction of the atrioventricular valve. The associated cor triatriatum, which had not been identified prior to surgery, presented difficulties during operation.     

The stepwise synthesis of methyl α-isomaltooligoside derivatives and methyl α-isomaltopentaoside

Methyl 2,3,4-tri-O-benzyl-α-D-glucopyranoside was treated with 2,3,4-tri-O-benzyl-6-O-(N-phenylcarbamoyl)-1-O-tosyl-D-glucopyranose in diethyl ether to give methyl 2,3,4,2',3',4'-hexa-O-benzyl-6'-O-(N-phenylcarbamoyl)-α-isomaltoside. The disaccharide was decarbanilated in ethanol with sodium ethoxide to give methyl 2,3,4,2',3',4'-hexa-O-benzyl-α-isomaltoside. The sequence of coupling with the same 1-O-tosyl-D-glucose derivative followed by removal of the N-phenylcarbamate group was repeated until the hexasaccharide derivative, methyl octadeca-O-benzyl-α-isomaltohexaoside, was formed. Methyl α-isomaltopentaoside was prepared by debenzylation of the corresponding benzylated oligosaccharide. The structures of the oligosaccharides were determined with the aid of both ¹H- and ¹³C-n.m.r. spectroscopy. From spectral data, we estimate the coupling reaction to be 95% stereoselective.     

Vitamin A in liposomes. Inhibition of complement binding and alteration of membrane structure.

Incorporation of vitamin A aldehyde (retinal) into liposomes had an inhibitory effect on the amount of human complement protein bound in the presence of specific antiserum. The total membrane-bound protein was directly measured on liposomes which were washed after incubation in antiserum and fresh human serum (complement). At every concentration of complement, decreased protein binding was found with liposomes which contained retinal. Binding of the third component of complement (C3) was also measured directly on washed liposomes and was found to be decreased in the presence of retinal. The diminution in protein binding due to retinal was not caused by differences in the amount of antibody bound and this was shown by two experiments. First, specific antibody protein binding to liposomes was directly measured and was essentially unaffected by retinal. Second, liposomes were prepared from lipid extracts of sheep erythrocytes. These liposomes were used as as immunoadsorbants to remove antisheep erythrocyte antibodies. The immunoadsorbant capacity was the same in both the presence and the absence of retinal. A further conclusion from these experiments was that retinal did not change the number of liposomal glycolipid antigen molecules available for antibody binding and thus presumably did not change the total number of lipid molecules present on the outer surface of the liposomes. Retinal did have an effect on the geometric structure of the liposomes. Size distribution measurements were performed in the diameter range of 1-6.35 mum by using an electronic particle size analyzer (Coulter Counter). Liposomes containing retinal were shifted toward smaller sizes and had less total surface area and volume. It was suggested that retinal-containing liposomes may have had a tighter packing of the molecules in the phospholipid bilayer. This effect of retinal on liposomal structure may have been responsible for the observed decreased binding of C3 and total complement protein.     

Kinetics of mucopolysaccharide and glycoprotein synthesis by chick embryo chondrocytes. Effect of D-glucose concentration in the culture medium.

Late log cultures of chick embryo vertebral chondrocytes in Dulbecco's Modified Eagle's Medium with 10% fetal calf serum consume D-glucose from the culture medium at a rate of approximately 0.40 mumol per h per 10(6) cells. When the D-glucose concentration in the medium drops below 1 mumol per ml the glycogen stores are rapidly exhausted, and cell growth ceases. 35SO4(2)- is incorporated into chondroitin-6-SO4 and chondroitin-4-SO4 at linear rates of 1.2 and 0.4 nmol per h per 10(6) cells, respectively, until the D-glucose level in the medium drops below 1 mumol per ml, but there is always a slight lag in the initial appearance of chondroitin-4-SO4. Throughout the period of 35SO4 2- labeling, the amount of chondroitin-6-SO4 that is recovered in the cells exceeds the amount that is recovered in the medium, but the opposite is true for chondroitin-4-SO4. However, when cells prelabeled with 35SO4(2-) are then transferred to a label-free medium, the secretion of chondroitin sulfates proceeds at much slower rates, and the kinetics of chondroitin-6-SO4 and chondroitin-4-SO4 secretion are very similar. In this chase experiment the chondroitin sulfates are recovered quantitatively after a 24-h incubation period, indicating that these embryonic chondrocytes do not degrade the chondroitin sulfates under these culture conditions. The rate of incorporation of counts from D-[14C]glucosamine into mucopolysaccharides and glycoproteins increase with time. This nonlinear rate results from a progressive increase in the specific activity of the UDP-N-acetyl-D-[14C]hexosamine pool as the D-glucose in the culture medium is depleted. A linear relationship is demonstrated between the logarithm of the 14C counts per min per nmol of UDP-N-acetylhexosamine and the logarithm of the concentration of D-glucose in the culture medium over a range of 1 to 20 mumol of D-glucose per ml. The relative rates of appearance of counts from 35SO4(2-) and D-[14]glucosamine in chondroitin 4-SO4 and chondroitin-6-SO4 are used to calculate the specific activity of the UDP-N-acetyl-D-[14C]hexosamine pool at each stage in the labeling period. The resulting values are then used to calculate the rates of synthesis of the nonsulfated polymers, namely, chondroitin, hyaluronic acid, and glycoprotein.     

Effect of oral contraceptives and pregnancy on erythrocyte deformability and surface charge.

Erythrocyte deformability and surface charge were studied in normal premenopausal women, oral contraceptive users, and pregnant women. The increased incidence of thrombosis in women taking oral contraceptives could not be explained by decreased erythrocyte deformability or surface charge. However, the decreased erythrocyte deformability of late pregnancy may relate to thrombosis during this period and to increased hemolysis in patients with certain hemoglobinopathies.     

Environmental history and physiological state influence feeding responses of Atrina zelandica to suspended sediment concentrations

Epifaunal suspension-feeding bivalves can play important roles in marine ecosystems affecting macrobenthic communities, benthic boundary layers and benthic-pelagic coupling, not just by their presence but also by any changes in feeding behaviour. While seston quality and quantity have consistently been found to be important influences on the feeding rates of suspension-feeding bivalves, factors stressing individuals are also likely to be important, as they may affect energy-dependent thresholds of response. We postulated that (1) history of seston quantity would affect how suspension feeders deal with increases in total suspended particulates, and (2) high-seston concentrations would affect feeding rates more in individuals whose energy reserves were low after spawning. Three sites were selected for short-term (1 day) feeding experiments on the pinnid bivalve, Atrina zelandica. At one site, the experiment was run pre-and postspawning. Atrina exhibited high rejection of filtered particles (mostly 75% to 100%) and high organic absorption efficiencies (0.9-1) at all seston levels. Strong differences in the response of feeding behaviour to increased seston concentrations were observed between A. zelandica from the different sites, with lesser differences observed between times. The site-specific feeding responses to seston concentrations observed are likely to affect our ability to model responses of A. zelandica to sediment loading and to influence the importance of A. zelandica to benthic-pelagic coupling.     

Natural selection and the evolution of neutralism

The efficiency of evolutionary search increases as the density of acceptable proteins in a protein space increases. Populations caught in regions whose density is too low to support evolution can be pulled into high density regions by hitchhiking selection. As they move into such regions, the action of natural selection becomes more effective, yet these populations will satisfy conditions which lead to predictions made by neutral, so-called non-Darwinian models.