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Biomedical subjects

T M Forte

Publications and source records attributed to T M Forte.

At least 91 records · Page 5Linked to original sources
PubMed1984

Cord blood plasma lipoproteins inhibit mitogen-stimulated lymphocyte proliferation.

Lipoproteins were isolated from adult plasma and the umbilical cord blood plasma of newborn infants and were compared for their capacity to inhibit mitogen-stimulated [3H]thymidine uptake of adult peripheral blood mononuclear cells in vitro. Relative to the comparable adult lipoproteins, cord blood low density lipoproteins and high density lipoproteins inhibited mitogen stimulation at twofold to fourfold lower total protein concentrations. Apoproteins AI, B, and E were quantitated by radioimmunoassay of each of the adult and cord blood lipoprotein fractions. A strong correlation was observed between inhibitory activity and the amount of apoprotein E in the cord blood low and high density lipoproteins. Further evidence that lipoproteins containing apoprotein E accounted for the difference in suppressive activity of cord blood low and high density lipoproteins relative to the adult lipoproteins was obtained by selective removal of the apoprotein E-containing lipoproteins by using immunoaffinity chromatography or heparin-agarose adsorption. The results indicated that cord blood lipoproteins containing apoprotein E in association with apoproteins AI or B are capable of suppressing lymphocyte proliferation in vitro.

Adult↗
PubMed1983

Actin and associated proteins in gastric epithelial cells.

A quantitative assessment of the distribution and state of microfilament-related proteins in the heterocellular fundic gastric epithelium was carried out. Actin content, as determined by the DNAase inhibition assay, ranged from 29 to 42 micrograms/mg of tissue protein, depending upon the tissue source. About 60% of the total actin existed in fresh tissue in the polymeric form (F-actin). The distribution of fluorescent-labelled phallicidin demonstrated that F-actin was concentrated predominantly in the acid-secreting oxyntic cells. The patterns of distribution corresponded to the location of the numerous elongated apical surface microvilli seen within oxyntic cell canaliculi. In the isolated apical membrane, actin represented about 10% of the total protein and was present entirely as F-actin. After mild treatment of membranes with Triton X-100, filaments could be readily visualized by negative staining. More extensive Triton X-100 extraction solubilized intrinsic membrane protein and yielded an insoluble residue highly enriched in actin and containing several additional polypeptides. Homogenization and fractionation of the gastric epithelium in low ionic strength media led to the depolymerization of a significant proportion of the tissue actin which was recovered in the homogenate supernatant. When purified by DNAase affinity chromatography, this gastric actin displayed structural and functional properties similar to muscle actin. Incubation of the homogenate supernatant in KCl-Mg2+ induced the formation of actin-rich gels. The gels contained myosin as well as several other peptides that may be actin-binding proteins.

Actins↗
PubMed1983

Apolipoprotein and size heterogeneity in human umbilical cord blood low density lipoproteins.

Neonatal umbilical cord blood plasma low density lipoproteins (LDL, d = 1.019-1.063 g/ml) were subfractionated by density gradient ultracentrifugation into seven fractions (from 1.024 to 1.062 g/ml); the bulk of the LDL mass was in a density region of 1.034-1.042 g/ml. Apolipoprotein B by 10% SDS-polyacrylamide gel electrophoresis varied inversely with density, with only trace amounts present in the most dense fraction. The distribution of apolipoprotein B molecular weight forms was assessed by both 3% SDS-polyacrylamide gel electrophoresis and relative aminoacyl mass determination. Lower molecular weight forms of apolipoprotein B (B74 and B26) increased relative to apolipoprotein B100 with increasing density, ranging from undetectable in fraction 1 to apolipoproteins B26 and B74 comprising 30% of the total mass of apolipoprotein B in fraction 6. No apolipoprotein B48 was detectable in the LDL. Apolipoprotein E as determined by both SDS-polyacrylamide gel electrophoresis and radioimmunoassay increased with density with a maximum (14% of the protein) in the most dense fraction, fraction 7. Apolipoprotein A-I by SDS-polyacrylamide gel electrophoresis increased with increasing density and was the major apolipoprotein in fraction 7. Electron microscopic analysis revealed spherical particles whose diameters decreased with increasing density, ranging from 28.6 nm in the top fraction (fraction 1) to 15.6 nm in the bottom fraction (fraction 7). Gradient gel electrophoresis revealed that most of the fractions contained several different sized particles. The bottom fraction (fraction 7), enriched in apolipoproteins E and A-I, had a unique, poorly defined peak at 14.6 nm on gradient gel electrophoresis and showed a tendency to pack hexagonally upon electron microscopy. The unusual composition and apolipoprotein distribution in neonatal LDL fractions suggests that the LDL in the neonate are metabolically very diverse.

Apolipoproteins↗
PubMed1983

Characterization of discoidal complexes of phosphatidylcholine, apolipoprotein A-I and cholesterol by gradient gel electrophoresis.

Complexes of egg yolk phosphatidylcholine and apolipoprotein A-I were prepared by a detergent (sodium cholate)-dialysis method and characterized by gradient gel electrophoresis, gel filtration, electron microscopy and chemical analysis. Multicomponent electrophoretic patterns were obtained indicating formation of at least eight classes of discoidal complexes. The relative contribution of the different classes to the electrophoretic pattern was a function of the molar ratio of phosphatidylcholine:apolipoprotein A-I in the interaction mixture. Molar ratios of phosphatidylcholine:apolipoprotein A-I in isolated complexes were strongly and positively correlated with disc diameter obtained by electron microscopy. Incorporation of unesterified cholesterol into phosphatidylcholine/apolipoprotein A-I interaction mixtures also resulted in formation of unique complexes but with considerably different particle size distributions relative to those observed in the absence of cholesterol. One common consequence of cholesterol incorporation into interaction mixtures of 87.5:1 and 150:1 molar ratio of phosphatidylcholine:apolipoprotein A-I was the disappearance of a major complex class with diameter of 10.8 nm and the appearance of a major component with diameter of approximately 8.8 nm. Electrophoretic patterns of cholesterol-containing complexes showed a strong similarity to patterns recently published for high density lipoproteins from plasma of lecithin:cholesterol acyltransferase-deficient subjects, suggesting that the complexes formed in vitro by the detergent-dialysis method may serve as appropriate models for investigation of the origins of the HDL particle size distribution.

Apolipoprotein A-I↗
PubMed1983

Composition and distribution of low density lipoprotein fractions in hyperapobetalipoproteinemia, normolipidemia, and familial hypercholesterolemia.

Hyperapobetalipoproteinemia is defined as the combination of a normal low density lipoprotein (LDL) cholesterol in the face of an increased LDL apolipoprotein B (apoB) protein. To examine the physical basis for the apparent disproportion between LDL cholesterol and apoB characteristic of this syndrome, we used density gradient ultracentrifugation to isolate LDL fractions from 10 normal subjects, from 20 patients with hyperapobetalipoproteinemia (10 normotriglyceridemic and 10 hypertriglyceridemic), and from 7 patients with familial hypercholesterolemia. In familial hypercholesterolemia, more LDL was in fraction 1--"light" LDL--and this LDL was relatively enriched in cholesterol and poor in protein. By contrast, it was fraction 2--"heavy" LDL--that differed in hyperapobetalipoproteinemia, being denser, depleted of cholesterol (particularly cholesteryl ester), and relatively enriched in apoB. These findings were more pronounced in the hypertriglyceridemic patients than in the normotriglyceridemic patients with hyperapobetalipoproteinemia. Thus this study confirms that considerable heterogeneity exists between LDL subfractions within individuals but, in addition, indicates there are also marked--and apparently characteristic--differences in LDL composition amongst normal subjects and patients with hyperapobetalipoproteinemia or familial hypercholesterolemia.

Apolipoproteins↗
PubMed1983

Correlation of parietal cell structure and function.

The apical surface of the gastric parietal cell is greatly expanded (5-10-fold) during maximal HCl secretion, as compared to the resting cell. The membrane recycling hypothesis has been proposed to account for the extensive, functionally related, rearrangement of cell membranes. Cytoplasmic membranes within the resting cell, the tubulovesicles, contain the H+/K+-ATPase. Fusion of tubulovesicles with the apical plasma membrane occurs when the cells are stimulated, thus providing the increased surface area and proper disposition of the H+ pump enzyme. Microfilaments, composed of actin and other regulatory proteins, serve to direct the reordering of the apical surface during stages of the secretory cycle. Cell fractionation of resting oxyntic mucosa reveals that virtually all of the H+/K+-ATPase activity is associated with light microsomal membrane vesicles, presumably derived from tubulovesicles. Although the enzyme from resting tissue is fully competent (e.g. ATP-driving pump, H+-K+ exchange), the microsomal vesicles lack an endogenous pathway to provide rapid access for K+ to its intravesicular activity site. In stimulated stomach, there is a redistribution of H+/K+-ATPase to a larger, denser membrane fraction, the so-called stimulation-associated vesicles. Morphological features and chemical content (e.g. microfilament proteins) suggest that the stimulation-associated vesicles are derived from the expanded apical surface of the stimulated oxyntic cell. A KCl cotransport system has been identified in the stimulation-associated membranes, which operates in parallel with the ATP-driven H+-K+ exchange pump. These two transport systems operate in concert within the apical membrane to provide the machinery for net HCl transport by the parietal cell.

Actins↗
PubMed1983

Characterization of sheep lung lymph lipoproteins: chemical and physical properties.

We have determined the composition and distribution of plasma and lung lymph lipoproteins from unanesthetized ewes. Cholesterol, triglyceride, and phospholipid levels in lung lymph were 45%, 50%, and 50%, respectively, of those in plasma. Lipoproteins from both lymph and plasma were separated into two major fractions: d less than 1.063 g/ml or "LDL", and d 1.063-1.21 g/ml or HDL. HDL was the major lipoprotein species in the plasma and lymph. Gradient gel electrophoresis of HDL on 4-30% gels showed that, in lymph, HDL particles were shifted to larger sizes; in addition to a peak at 8.5 nm, which was similar to plasma HDL, there were two additional components of larger size, one at 9.2 nm and the other at 12 nm. Electron microscopy revealed that lymph HDL contained two new particles not seen in plasma: large, round particles, 13.6 nm diameter, and discoidal particles, 18.7 by 4.9 nm, long and short axis, respectively. Compositional analysis of lymph HDL revealed a relative enrichment in free cholesterol as well as an enrichment in apolipoprotein E. Lymph "LDL" on gradient gel electrophoresis was extremely heterogeneous. Several peaks were evident in the 23-30 nm size range (similar to plasma "LDL"), but a supplementary component at approximately 15-16 nm was also present. Whereas plasma "LDL" on electron microscopy contained only round particles 26 nm in diameter, lymph contained an additional, unusual particle which was close-packed, with square geometry, and was 15 nm in diameter. Lymph apolipoprotein composition differed from that of plasma by the appearance of apoE and A-I as well as apoB. Particles containing apoE and A-I were separated from apoB-containing particles in a fraction of d 1.047-1.063 g/ml by density gradient centrifugation. On electron microscopy, this fraction revealed square-packing particles; the density and apolipoprotein composition suggest that these unusual particles are a continuum of HDL. Changes in the physical and chemical properties of lung lymph lipoproteins suggest that these particles are metabolically modified.

Animals↗
PubMed1983

Lipoprotein distribution in sheep lung lymph.

The composition of lymph draining the sheep caudal mediastinal lymph node is believed to reflect the composition of lung interstitial fluid. Although long-term lymph fistulas have been extensively utilized in studies related to lung microvascular fluid and protein flux, attention has thus far not been focused on lipoproteins as they might appear in lung interstitial space. We therefore characterized the lipoprotein distributions and measured triglyceride and cholesterol concentrations of lung lymph and plasma in nine unanesthetized sheep with long-term embedded instrumentation. We also measured triglyceride and cholesterol concentrations in prefemoral and thoracic duct lymph. The plasma LDL concentration was 55.3 +/- 20.2 mg/dl and HDL concentration was 99.9 +/- 27.2 mg/dl. By comparison, the lung lymph LDL concentration was 27.7 +/- 3.0 mg/dl and the HDL concentration was 45.4 +/- 11 mg/dl. The major sheep lipoprotein classes (LDL, HDL), although low in concentration compared to humans, are present in lung lymph in relative proportions similar to those of plasma. Analytical ultracentrifugation revealed the presence of a fast-floating component in lung lymph HDL that was not present in plasma. Electron microscopy showed two sizes of particles in lung lymph HDL, 135A and 97A, which probably correspond to the fast-floating and slow-floating components, respectively; plasma HDL contained only 94 A particles. Changes in the physical properties of HDL present in lung lymph suggest modification of the HDL either in the endothelial barrier or interstitial fluid of the lung.

Animals↗
PubMed1982

The effects of microfilament disrupting agents on HCl secretion and ultrastructure of piglet gastric oxyntic cells.

A functionally responsive in vitro preparation of piglet gastric mucosa was used to investigate the involvement of microfilaments in the process of HCl secretion by oxyntic cells. A well-ordered array of microfilaments was observed in the short, stubby microvilli on the apical surface of nonsecreting oxyntic cells, as well as ii the longer microvilli of actively secreting cells. Treatment with cytochalasin B (10(-5)-10(-4) M) caused a dose-dependent inhibition of acid secretion and a concomitant gradient of morphologic alteration of oxyntic cells. Associated with slight (approximately 20%) inhibition of secretion was an initial collapse of the canalicular and glandular lumina and appearance of some pleomorphic-shaped microvilli. Maximum inhibition of secretion always produced a complete collapse of the oxyntic cell canalicular and glandular lumina, with a resultant apposition of apical surfaces. Microvilli were no longer readily distinguishable, and microfilaments were severely disorganized. Treatment with cytochalasin B (2-4 X 10(-5) M) before secretagogue stimulation also reduced the ability of the gastric mucosa to secrete acid; oxyntic cells retained the general appearance of nonsecreting cells. The correlation of disruption of microfilaments and the inhibition of acid secretion by cytochalasin B suggests an involvement of microfilaments in both the initiation and maintenance of high levels of acid secretion.

Animals↗
PubMed1982

The electron microscopic structure of human umbilical cord blood lipoproteins.

Neonatal VLDL, LDL, HDL2 and HDL3 were isolated from umbilical cord blood by preparative ultracentrifugation and analyzed by electron microscopy. Cord blood VLDL were round particles that were heterogeneous in size, mean diameter 49.5 +/- 10.3 nm. This size was very similar to that of the normal adult population. Cord blood LDL had a mean diameter of 25.9 +/- 3.4 nm. Most LDL particles were round in profile, but there was always a small fraction of particles which had flattened sides and formed short, linear aggregates. These latter structures may represent a metabolically distinct subpopulation of particles although their origin is unknown. Cord blood HDL3 were homogeneous round particles indistinguishable from those of the adult, and they had a mean diameter of 8.8 +/- 1.4 nm. HDL2 from cord blood had a mean diameter of 11.5 +/- 1.7 nm and are larger than the adult population. The HDL2 were characterized by the presence of small amounts of rectangular-shaped structures, 14.0 by 10.0 nm in size. These latter particles are enriched in the density fraction d 1.095 g/ml and are unique to the cord blood HDL. The presence of these unusual particles suggests that cord blood HDL may transport lipids in a somewhat different fashion from that of normal adult HDL.

Adult↗
PubMed1981

Characterization of human high-density lipoproteins by gradient gel electrophoresis.

Gradient gel electrophoresis in conjunction with automated densitometry was applied to the identification and estimation of subpopulations of high-density lipoproteins (HDL) in the ultracentrifugal d less than or equal to 1.200 fraction from human plasma. The frequency distribution of relative migration distances (RF values) of subpopulation peaks in HDL patterns of a group (n = 194) of human subjects showed five apparent maxima: two in the RF range associated with the HDL2 subclass, and three in the RF range of the HDL3 subclass. HDL within RF intervals bounding these maxima were designated (HDL2b)gge, (HDL2a)gge, (HDL3a)gge, (HDL3b)gge and (HDL3c)gge and were shown to correspond approximately to material determined by analytic ultracentrifugation within the HDL2b, HDL2a and HDL3 components. Material represented by the HDL2a component, as resolved by three-component analysis of the ultracentrifugal Schlieren pattern, was found by gradient gel electrophoresis to be polydisperse in particle size. Mean hydrated densities and particle sizes of HDL corresponding to those with RF values of the frequency maxima were: 1.085 g/ml and 10.57 nm in the (HDL2b)gge; 1.115 g/ml and 9.16 nm in the (HDL2a)gge; 1.136 g/ml and 8.44 nm in the (HDL3a)gge; 1.154 g/ml and 7.97 nm in the (HDL3b)gge; and 1.171 g/ml and 7.62 nm in the (HDL3c)gge. The mean hydrated density values of the subpopulations within the (HDL3a)gge and (HDL3b)gge were comparable to those of the HDL3L and HDL3D components recently characterized by zonal ultracentrifugation. High order and statistically significant correlations between densitometric scans of the (HDL2b)gge, (HDL2a)gge and (HDL3)gge material, as obtained from gradient gels, and plasma concentrations of the HDL2b, HDL2a and HDL3 components, as obtained from analytic ultracentrifugation, were demonstrated.

Adult↗
PubMed1981

Ultrastructural changes related to functional activity in gastric oxyntic cells.

When stimulated to secrete HCl the gastric oxyntic cell undergoes profound morphological change. The identifiable apical cell surface is greatly expanded in the stimulated oxyntic cell as compared with nonsecreting ones. To account for this change, one hypothesis proposes that the expanded surface is derived from the fusion of cytoplasmic tubulovesicular membranes with the existing limited apical membrane surface. An alternative hypothesis suggests that the tubulovesicular compartment is actually confluent with the apical surface at all times and that the morphological appearance follows the expansion of this supercollapsed compartment as HCl secretion commences. A variety of morphological evidence is reviewed here including transmission electron microscopy during various stages of secretion and inhibition, analysis of freeze-fracture replicas, penetration of macromolecular tracers, and membrane surface-staining characteristics. It is concluded that the weight of evidence favors a membrane fusion process. Moreover, recent comparative studies of membrane fractions from resting and secreting stomachs show different morphological and functional properties that are also consistent with a fusion hypothesis as a fundamental event in the membrane transformation of the oxyntic cell.

Animals↗
PubMed1981

Heterogeneity of serum low density lipoproteins in normal human subjects.

Equilibrium density gradient ultracentrifugation of serum low density lipoprotein (LDL) from twelve healthy human subjects was used to separate six subfractions with mean density ranging from 1.0268 to 1.0597 g/ml. Mean corrected peak flotation rate (Sof) measured by analytic ultracentrifugation, and mean particle diameter determined by negative staining electron microscopy, both declined significantly with increasing density of the subfractions. Major differences in chemical composition of the subfractions were noted, including a significantly lower triglyceride content and higher ratio of cholesteryl ester to triglyceride in the middle fractions compared with those of highest and lowest density. Concentration of fraction 2 correlated positively with HDL (P less than 0.01) and negatively with VLDL (P less than 0.001); concentration of fraction 4 correlated negatively with HDL (P less than 0.05) and positively with VLDL (P less than 0.001) and IDL (P less than 0.01). LDL may thus include subspecies of differing structure and composition which might also have different metabolic and atherogenic roles.

Adult↗
PubMed1981

Inhibition of HCl secretion and the effects on ultrastructure and electrical resistance in isolated piglet gastric mucosa.

Rates of H+ secretion and transepithelial resistance were measured for gastric mucosas from neonatal piglets before and after the addition of histamine and with the deployment of conditions that inhibit HCl secretion. At designated times tissue biopsy specimens were taken and prepared for electron microscopy. Oxyntic cell morphology was evaluated by classification of the cells into one of four categories: resting, partially stimulated, stimulated, or returning. Morphologic profiles for each experimental condition were thus established. In order to assess this method of quantitation, detailed morphometric analyses of oxyntic cells from resting and stimulated preparations were undertaken. The observed differences in tubulovesicular and microvillar surface densities were similar to those of previous investigators and correlated well with the morphologic profiles for these conditions. Actively secreting gastric preparations subjected to 15 mM NaSCN, substrate deprivation, or removal of histamine showed an inhibition of HCl secretion coupled with an increase in tissue resistance. However, only the morphologic profile of cells from the latter condition was different from that observed for control stimulated cells; histamine removal caused cells to be predominantly of a resting or returning morphology. Treatment of resting tissue with SCN- or removal of substrate inhibited subsequent histamine-induced secretion though tissue resistance decreased somewhat (approximately 15%). The morphologic profile of cells from these conditions was similar to that of control stimulated cells, despite the lack of acid secretion. These data support the hypothesis that oxyntic cell morphology does not absolutely dictate the secretory state of the tissue and that the resistance of gastric mucosa cannot be accounted for solely by the ultrastructure (i.e., surface area) of oxyntic cells.

Animals↗
PubMed1980

Interaction of human plasma high-density lipoprotein HDL2b with discoidal complexes of dimyristoylphosphatidylcholine and apolipoprotein A-I.

The interaction of HDL2b, a major subclass (d = 1.063 - 1.100 g/ml) of human plasma high-density lipoproteins, with discoidal complexes composed of dimyristoylphosphatidylcholine (DMPC) and apolipoprotein A-I (weight ratio, DMPC/apolipoprotein A-I (2.1 - 2.5:1); dimensions, 10.0 x 4.4 nm) was investigated. Incubation at 37 degrees C for 4.5 h of HDL2b with discoidal complexes resulted in a transfer of DMPC from the discoidal complexes to the HDL2b, a release of lipid-free apolipoprotein A-I from the discoidal complexes during such transfer, and a dissociation of some apolipoprotein A-I from the HDL2b surface. The number of discoidal complexes degraded during interaction with HDL2b depended on the initial molar ratio of HDL2b to discoidal complexes. Approximately one molecule of HDL2b was required for the degradation of one discoidal complex particle, and the degradation process appeared limited by the capacity of the HDL2b for uptake of DMPC. Degradation of discoidal complexes was also observed when human plasma LDL (d = 1.006-1.063 g/ml) was substituted for HDL2b in the interaction mixture.

Adult↗