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Biomedical subjects

T M Forte

Publications and source records attributed to T M Forte.

At least 109 records · Page 6Linked to original sources
PubMed1980

Structure of oxyntic cell membranes during conditions of rest and secretion of HCl as revealed by freeze-fracture.

The density and distribution of membrane associated particles of piglet oxyntic cell tubulovesicular and apical surface membranes were investigated during resting (nonsecreting) and secreting conditions. For the resting oxyntic cell, the abundant tubulovesicles showed a highly asymmetrical distribution of particles between fracture faces, with the P face heavily studded by particles and the E face particle deficient. The apical surface, however, had a relatively symmetrical distribution of particles on both membrane fracture faces. In contrast to the resting state, the apical surface of the stimulated oxyntic cell showed a marked asymmetry of membrane particles; the P face had a high density of particles, while there was a scarcity of particles on the E face. The observed changes in apical surface membrane particle distribution support the hypothesis that, following the initiation of acid secretion, the tubulovesicles fuse with and become an integral part of the apical surface. Thus, the apical membrane P face of the stimulated cell is enriched and the E face is diluted by the incorporation of tubulovesicular membranes.

Animals↗
PubMed1979

Dissociation of apolipoprotein A-I from porcine and bovine high density lipoproteins by guanidine hydrochloride.

Dissociation of apolipoprotein A-I from pig and steer high density lipoproteins (HDL) deficient in apoA-II was determined by exposing native HDL fractions to 6 M guanidine hydrochloride (Gdn-HCl) at 37 degrees C for periods from 5 min to 18 h. Bovine high density lipoprotein (HDL-B) was isolated at d 1.063--1.100 g/ml while porcine high density lipoprotein (HDL-P) was isolated at d 1.125--1.21 g/ml. Incubation for 5 min with Gdn-HCl resulted in a 45 and 3% loss of apo-A-I from HDL-P and HDL-B, respectively. Exposure to the denaturant for 3 h resulted in a 75% loss of apoA-I from HDL-P and a 30% loss from HDL-B. Analytic ultracentrifugation, patterns paralleled the degree of apoA-I dissociation from each HDL species. The initial flotation peak for HDL-P shifted from F degrees 1.20 2.68 to F degrees 1.20 10.75 after 3 h exposure while HDL-B showed only a small shift from F degrees 1.20 8.30 to F degrees 1.20 8.96 after 3 h exposure. HDL-P particle diameter increased 25% after 5 min of Gdn-HCl treatment and large, flattened structures predominated after 3 h. There was no changes in the size of HDL-B after 5 min exposure and only 16% increase in particle diameter after 3 h. The difference in behavior of HDL-B and HDL-P to Gdn-HCl exposure is discussed in terms of differences in apolipoprotein A-I amino acid composition, interaction of apolipoprotein A-I with phospholipids and the possible involvement of the cholesteryl ester core.

Amino Acids↗
PubMed1979

Changes in plasma lipoprotein distribution and formation of two unusual particles after heparin-induced lipolysis in hypertriglyceridemic subjects.

Lipoprotein morphology and distribution were studied in three moderately to severely hypertriglyceridemic patients after heparin-induced lipolysis. Lipoproteins with a flotation rate of Sf degrees 12-20 in rho 1.063-g/ml NaCl solution increased substantially in mass 2.5-10 min after heparin administration. This fraction contained 40- to 120-nm flattened particles and increased concentrations of phospholipid and free cholesterol. At 2.5 and 10 min after heparin, the high density lipoproteins (HDL) of rho, 1.126-1.21 g/ml contained small (5.8-nm diameter) spherical particles. Both types of particles disappeared 30-60 min after heparin. Results indicated that with lipolysis HDL3 may be transformed into HDL2a by incorporation of chylomicron and very low density lipoprotein constituents. It is suggested that the 40- to 120-nm particles represent surface fragments of chylomicrons and very low density lipoproteins generated during lipolysis, whereas the 5.8-nm particles are produced either by fragmentation of the large surface constituents or by loss of lipid from existing HDL3.

Chylomicrons↗
PubMed1977

Particle distribution of human serum high density lipoproteins.

Density gradient ultracentrifugation of human serum high density lipoproteins (HDL) from both normolipemic males and females results in a distribution of HDL concentration versus subfraction hydrated density which has three maxima. Gradient gel electrophoresis of total HDL is characterized by three banding maxima, the positions of which suggest the presence of three particle size ranges: I. 10.8-12.0 nm, II. 9.7-10.7 nm, and III. 8.5-9.6 nm. Gradient gel electrophoresis of density gradient subfractions established an inverse relationship between particle size and particle hydrated density which was corroborated by electron microscopy and analytic ultracentrifugation. Comparison of male HDL from size ranges I, II, and III with female HDL from the same size ranges showed only small differences in the mean value of the peak F degrees 1.20 rate, size, molecular weight, protein weight percent, and weight protein/weight phospholipid. Major differences between males and females were seen in the relative amounts of HDL in density gradient subfractions 1-3 (size range I material) and 11-12 (size range III material); the percent total HDL in the group of subfractions 1-3 was greatly increased in female HDL while that of the group of subfractions 11-12 was increased in the male HDL. These studies indicate the presence of at least three major components in HDL instead of two (HDL2 and HDL3) and that peak F degrees 1.20 rate differences in HDL schlieren patterns between males and females are a function of the relative levels of these three components.

Centrifugation, Density Gradient↗
PubMed1976

Effects of guanidine hydrochloride on human plasma high density lipoproteins.

Denaturation of human plasma high density lipoproteins during ultracentrifugation in guanidine-HCl is characterized by: dissociation of apoA-I, in the range of 2-3 M guanidine-HCl, and dissociation of apoA-I and apoA-II in 5-6 M guanidine-HCl. Denaturation of high density lipoprotein species, during a sequence of timed exposure to guanidine-HCl followed first by removal of the denaturant by dialysis and then by ultracentrifugation, is characterized by:dissociation of lipid-poor apoA-I, which follows a time course similar to denaturation-related changes in reported spectroscopic parameters; and apparent formation of lipoprotein aggregation products depleted in apoA-I and relatively enriched in apoA-II. These studies indicate differential properties of the major apoproteins in stabilizing high density lipoprotein structure and characterize a mode of lipoprotein transformation and degradation which apparently results from apoprotein dissociation coupled with aggregation of denatured lipoprote species.

Adult↗
PubMed1975

Structural and compositional changes attending the ultracentrifugation of very low density lipoproteins.

The effects of repetitive ultracentrifugation on the physical and chemical properties of very low density lipoproteins (VLDL) were investigated. VLDL recentrifuged one to seven times were characterized by chemical analyses, analytical ultracentrifugation and electron microscopy. The VLDL content of triglyceride was increased and the proportion of phospholipid decreased by ultracentrifugation. Recentrifugation of VLDL decreased the number of Sf-o 20-100 particles and generated particles of Sf-o greater than 400. The bulk of the material removed from VLDL by ultracentrifugation was lipoprotein having pre-beta mobility on paper electrophoresis, flotation rates of Sf-o 10-100 and a particle size of 300-400 A-O. Two ultracentrifugations separated an average of 14% of the starting VLDL protein. Characterization of the apoproteins in this material by polyacrylamide gel electrophoresis, gel chromatography, immunoprecipitation and amino acid analysis demonstrated a relatively high proportion of beta-apoprotein and relatively little C-apoproteins.

Adult↗
PubMed1975

Histamine-stimulated hydrogen ion secretion by in vitro piglet gastric mucosa.

1. A new preparation of gastric mucosa isolated from new-born piglets is described. The piglet gastric mucosa was easily separated from the serosal muscle layers by a "blistering" technique which appeared to cause minimal trauma to the tissue and which allowed extended study in vitro in a suitable chamber. Normal resting p.d. was approximately minus 30 mV (mucosal side negative with respect to serosal side), resistance about 100 omega. cm-2 and H+ secretion was absent or occurred at very low rates (0-1mu-equiv/cm-2. hr). 2. Maximally stimulating doses of histamine (1-6 times 10-5 M) caused H+ secretion to increase (up to 15 muequiv/cm-2. hr), p.d. to increase and resistance to decrease. A close correlation was observed between the increase in H+ secretion and decrease in transmucosal resistance. The threshold dose of histamine appeared to be 10-8 M; concentrations 10-4 M and higher reduced H+ secretion somewhat. 3. Pentagastrin ( 10-9-10-7 M) and acetylcholine (10-7-10-5 M) did not significantly stimulate the piglet gastric mucosa. Pentagastrin concentrations above 4 times 10-6 M reversibly inhibited H+ secretion of histamine-stimulated mucosa. High concentrations of acetylcholine (above 4 times 10-4 M) did not affect histamine-stimulated H+ secretion, but a significant reduction in p.d. was observed. 4. This investigation demonstrates the utility of the piglet gastric mucosa for in vitro studies of the mechanism H+ secretion and the action of secretagogues. From a consideration of such factors as the thinness of tissue and ease of preparation it is suggested that neonatal animals may represent a good source of in vitro mammalian gastric tissue.

Acetylcholine↗
PubMed1975

Ultrastructural and physiological changes in piglet oxyntic cells during histamine stimulation and metabolic inhibition.

Neonatal pig gastric mucosa was studied in order to correlate electrophysiological and secretory parameters with ultrastructural changes in membrane components of oxyntic cells. The non-stimulated tissue had a transmucosal resistance of about 130omega - cm2 while the oxyntic cells were characterized by numerous cytoplasmic tubulovesicles and short microvilli extending into patent glandular and canalicular lumina. Upon histamine-stimulation, the average rate of H+ secretion was 8.1 mueq - cm2 - hr-1 and the resistance decreased to 77omega - cm2. The changes were coupled with an immense elaboration of the oxyntic cell apical and canalicular surfaces with a concomitant decrease of tubulovesicles. Thus, the observed decrease in resistance was correlated to large increases in secretory membrane area. Anoxia inhibited H+ secretion while resistance increased to 211omega - cm2. Anoxic oxyntic cells were characterized by swollen mitochondria and occlusion of the lateral intercellular space and basal infoldings. Little change in the configuration of the secretory surfaces was noted, thereby suggesting that restriction of lateral and basal membranes might be responsible for the observed resistance increase. An electrical analogue of gastric mucosa is proposed on the basis of these morphological observations.

Animals↗
PubMed1975

Unique enzymes of purified microsomes from pig fundic mucosa. K+-stimulated adenosine triphosphatase and K+-stimulated pNPPase.

Microsomal fractions from homogenates of pig gastric fundic mucosa showed high levels of K+-stimulated adenosine triphosphatase (ATPase) and K+-stimulated phosphatase. Similar preparations from antral mucosa showed virtually no such activity. Because of mitochondrial contamination the fundic microsomes were further separated by sucrose density gradient centrifugation. A low density band of membranes (peak 1.12 to 1.13 g per ml) possessed all of the K+-stimulated enzyme activities. Morphological features and the abundant glycoproteins of the low density microsomes suggested they might be derived from the tubulovesicles of oxyntic cells. Mitochondrial and ribosomal markers were associated with membranes with much higher densities (greater than 1.22). The K+-stimulated ATPase has a pH optimum of 7.5 and required Mg++, but neither Na+ nor ouabain had any appreciable effect on the activity. Stimulation of basal ATPase by K+ ranged from 1.5 to 3.0-fold with an apparent Ka for activation between 0.2 to 0.4 mM K+. Addition of various K+ ionophoretic substances (e.g., gramicidin) produced further stimulation of K+-ATPase up to 6 times the basal rate. The mean activities for seven separate preparations of purified low density pig fundic microsomes were as follows (micromoles of ATP hydrolyzed per mg protein per hr +/- SEM); basal ATPase, 15.8 +/- 2.8; plus 10 mM K+, 29.3 +/- 4.5; plus 10 mM K+ and 10(-5) M gramicidin, 45.2 +/- 5.2. Neither the basal ATPase nor the K+-stimulated rates were altered by HCO3- or Cl-. The occurrence of these active and unique enzyme activities in the oxyntic region of gastric mucosa suggest some relation with secretory activity. Possible functional roles are discussed.

4-Nitrophenylphosphatase↗
PubMedDate not supplied

Neonatal umbilical cord blood lipoproteins. Isolation and characterization of intermediate density and low density lipoproteins.

Intermediate density lipoproteins (IDL) (d = 1.006 to 1.019 g/ml) and low density lipoproteins (LDL) (d = 1.019 to 1.063 g/ml) were isolated from human umbilical cord blood plasma by sequential ultracentrifugation. The concentration, chemical and apolipoprotein composition, size and size distribution of the neonatal IDL and LDL for both sexes were determined. The IDL and LDL from the neonates showed no sex-related differences in composition or concentration. The IDL and LDL were lower in concentration and differed in composition of concentration. The IDL and LDL were lower in concentration and differed in composition with regard to each other and with regard to the comparable adult fractions. The apolipoprotein (apo) composition showed only the high molecular weight form of apo B present in the IDL, while the LDL showed the presence of two lower molecular weight forms of apo B in addition to the high molecular weight form, along with appreciable amounts of apo E and apo A-l. The size distribution of the neonatal IDL and LDL showed a constant pattern, with peaks at approximately 300 A for IDL and 257 and 244 A for neonatal LDL. The alterations in composition, size and size distribution, as well as the lower concentrations present in neonate, point to differences between the neonate and the adult in the metabolism of lipoproteins with a density of 1.006 to 1.063 g/ml.

Adult↗
PubMedDate not supplied

Electron microscopic structure of serum lipoproteins from patients with fish eye disease.

The structure and composition of lipoprotein fractions from two patients with fish eye disease were examined. The composition of very low density lipoproteins (VLDL) was normal, although total mass was greatly elevated. The mean particle sizes of the VLDL were 44.6 +/- 22.2 and 42.8 +/- 19.8 nm for Patients 1 and 2, respectively. Intermediate density lipoprotein (IDL) concentrations in patients were elevated and contained increased triglyceride content; particle sizes for Patients 1 and 2 were 29.4 +/- 3.5 nm and 28.0 +/- 4.1 nm, respectively. In both patients, the triglyceride/cholesteryl ester ratio in LDL was approximately tenfold higher than in normal individuals; however, the LDL particles were somewhat smaller in diameter (23.5 +/- 3.0 nm for Patient 1 and 23.3 +/- 3.8 nm for Patient 2) than those of controls (25.8 +/- 3.0 nm and 24.9 +/- 3.4 nm). In both patients, large vesicular structures were occasionally encountered in the LDL region. The high density lipoprotein (HDL) fraction of fish eye disease patients showed the greatest abnormalities. Not only was the total HDL concentration extremely low (approximately 10% of control levels), but unesterified cholesterol was increased relative to cholesteryl ester. Particle morphology was heterogeneous; the major HDL species was a small spherical particle with a diameter of 7.6 nm. Discoidal particles with a thickness of 4.4 nm and diameters between 17.4 and 20.8 nm were also present, together with large (40-90 nm) vesicles.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗