Biomedical subjects

K A Robinson

Publications and source records attributed to K A Robinson.

At least 91 records · Page 5Linked to original sources

PubMed1995

Chemical and immunological heterogeneity of fibrillar amyloid in plaques of Alzheimer's disease and Down's syndrome brains revealed by confocal microscopy.

Amyloid beta peptides (A beta) are deposited in the brains of Alzheimer's disease (AD) and elderly Down's syndrome (DS) patients in a variety of amyloid plaques. Among these are classical plaques composed of a spherical core and corona. Analyzing AD tissue sections single and double stained with anti-A beta antibodies and thioflavin S (thioS) by bright field, fluorescence, and confocal microscopy revealed that spherical plaque cores consist of a thioS-positive center and an anti-A beta antibody immunoreactive rim. This indicates that there is a fibrillar form of amyloid that is thioS positive but not immunoreactive with anti-A beta antibodies. In contrast, classical plaques in DS patients have irregular cores that are thioS positive as well as anti-A beta immunoreactive. In addition, a subset of plaques in both DS and AD patients have a distinct "fibrous" appearance when stained with thioS, but are amorphous when immunostained. These findings suggest that anti-A beta antibodies and thioS stain similar; as well as different forms of fibrillar amyloid. A beta may become thioS positive by interacting with one or more of its known molecular chaperons, and this may be important for the pathogenesis of AD, given that thioS-positive A beta deposits are associated with neuritic and synaptic damage.

Aged↗

PubMed1994

Isolation, sequence and characterization of the maltose-regulated mlrA gene from the hyperthermophilic archaeum Pyrococcus furiosus.

The mlrA (maltose regulated) gene from the hyperthermophilic archaeum Pyrococcus furiosus was identified from a family of clones whose expression was influenced by the presence of maltose in the medium. Sequencing of the 2276 bp of DNA containing mlrA and flanking regions revealed a 753-amino-acid (aa) (88 kDa) open reading frame (ORF). The ORF is preceded by a bacterial-like ribosome-binding site. The deduced product shared extensive homology with pyruvate dikinases (PDK) from both eukaryal and eubacterial sources (35-61% similarity) and the signature domains characteristic of this class of proteins were present. Northern blot experiments demonstrated the presence of an approx. 2.4-kb transcript in P. furiosus extracts, corresponding in length to that expected from expression of mlrA. P. furiosus cultures grown in the presence of maltose were found to contain approx. 5-10-fold greater mlrA mRNA than those grown without maltose. Initiation of transcription under both cultural conditions occurred at the same transcription start point (tsp), 23 bp downstream from a putative BoxA promoter element.

Amino Acid Sequence↗

PubMed1994

Delayed processing of the insulin proreceptor by hepatocytes from diabetic rats.

The effect of diabetes on insulin receptor processing was assessed in rat hepatocytes, 2-4 weeks after the induction of diabetes with streptozotocin. Isolated hepatocytes from control and diabetic rats were labelled for 30 min with [35S]methionine in methionine-free medium and chased with complete medium for 1-3 hrs. Solubilized cell extracts were immunoprecipitated with a site-specific anti-insulin receptor antibody, proteins were separated by electrophoresis and labelling quantified following autoradiography. After 1 hr chase, only the insulin proreceptor was labelled in both groups. After 3 hrs, the ratio of labelled proreceptors to labelled insulin receptors was 0.57 +/- 0.063 in controls and 1.33 +/- 0.24 in hepatocytes from diabetic rats. Insulin added in vitro did not affect transit time. Delayed processing of the insulin proreceptor may reflect altered N-glycosylation and may also involve other glycoproteins.

Animals↗

PubMed1994

Isolation of maltose-regulated genes from the hyperthermophilic archaeum, Pyrococcus furiosus, by subtractive hybridization.

The hyperthermophilic archaeum, Pyrococcus furiosus, utilizes maltose as a preferred carbon source for growth. 32P-labeled complementary DNA (cDNA) probes representing maltose-regulated genes were obtained by a subtractive hybridization procedure that minimized retrieval of ribosomal RNA (rRNA) sequences during screening. Genomic DNA clones were isolated by positive hybridization to these probes. Genes whose expression varied both in the level of transcription, relative to rRNA, as well as in the degree of regulation were obtained; the extent of regulation varied over a wide range, from as little as fivefold to as high as 50-100-fold. DNA sequence analysis of several of these regulated genes indicated that the subtraction library included gene products required for maltose utilization (e.g., pyruvate dikinase), as well as growth-rate-related genes such as those encoding ribosomal proteins and RNA polymerase subunits. Our approach is applicable to studying gene regulation in organisms that are not amenable to classical genetic techniques.

Archaea↗

PubMed1994

Effect of immobilization on glucose transporter expression in rat hindlimb muscles.

Three days after denervation, the expression of GLUT4 mRNA and protein decreases by approximately 50% in rat hindlimb muscles, while GLUT1 mRNA increases transiently by approximately 500%. Although postreceptor insulin resistance of glucose transport develops before GLUT4 declines, the latter likely contributes to the time-dependent increased severity of the resistance. To determine whether muscle inactivity contributes to changes in glucose transporter expression, one rat hindlimb was immobilized in a plaster cast for 3 days; the unencumbered hindlimb served as control. Muscle GLUT4 mRNA decreased by 32% (P < .02) and GLUT4 protein by 40% (P < .05) after 3 days' immobilization. There was no significant change in GLUT1 mRNA or skeletal muscle alpha-actin mRNA expression or in the total RNA concentration. The data suggest that electromyogenic and/or contractile activity regulates GLUT4 expression in skeletal muscle at a pretranslational step.

Actins↗

PubMed1994

Effects of left ventricular pressure on sonicated albumin microbubbles: evaluation using an isolated rabbit heart model.

OBJECTIVES: We used an isolated, crystalloid-perfused rabbit heart model to test the hypothesis that the phasic changes in left ventricular contrast are due to bubble compression and decompression during systole and diastole, respectively. BACKGROUND: Contrast enhancement of the left ventricular cavity has been shown to decrease during ventricular systole. This phenomenon has been attributed to pressure-induced microbubble destruction. Such destruction, if confirmed, would severely confound the quantitative interpretation of contrast echocardiographic data. METHODS: A fixed volume of contrast solution (5% human albumin and Albunex, approximately 400:1 ratio) was introduced into a latex balloon placed within the left ventricular cavity of an isolated paced rabbit heart preparation (n = 12). Instantaneous left ventricular pressure was measured using a high fidelity microtip catheter and digitized on-line. The beating heart was placed in a water tank, and ultrasound images were obtained using a 7.5-MHz transducer and were recorded and digitized off-line at 12 frames/s. Simultaneously, the pacing signal was used for gated on-line acquisition of end-diastolic frames. A simple theoretic model based on surface tension physical principles was used to predict changes in bubble size and, consequently, the reflection intensity in response to the measured changes in left ventricular pressure. RESULTS: We found that under peak left ventricular systolic pressures ranging from 89 to 155 mm Hg, 1) end-diastolic videointensity decreased by 8 +/- 6% (mean +/- SD) over 25 consecutive heart beats; and 2) intracyclic variations in measured videointensity were in close agreement with the theoretic calculations: 80.1 +/- 2.9% versus 80.2 +/- 4.6% of diastolic videointensity at systole. CONCLUSIONS: The major cause of systolic decrease in contrast enhancement is periodic bubble compression (as opposed to bubble destruction) induced by high systolic pressures. The minor progressive decrease in end-diastolic videointensity reflects the degree of instability of Albunex microbubbles under left ventricular pressures. However, the clinical impact of these destructive effects is likely to be only minor because of the rapid transit of microbubbles through the left heart chambers and myocardial microcirculation.

Albumins↗

PubMed1993

Use of the porous balloon in porcine coronary arteries: rationale for low pressure and volume delivery.

Using agents administered systemically, attempts to control the restenotic myoproliferative response associated with angioplasty have been unsuccessful. The porous balloon has the advantage of achieving high local concentrations by directly infusing agents into the arterial wall. The purpose of this study is to identify any acute and chronic morphological changes in swine coronary arteries infused with normal saline through the porous balloon at different driving pressures. In order to establish the safety of local arterial wall infusion through the porous balloon, swine underwent porous balloon infusion of 3, 6, or 10 ml of saline at 5 atmospheres, or infusion of 3 ml of normal saline delivered at either 2, 5, or 10 atmospheres of pressure into the normal left anterior descending and left circumflex arteries. To assess the histopathologic alterations induced by the porous balloon, sized 1.1 to 1 with respect to the artery, animals were sacrificed either immediately after porous balloon infusion or 14 ays later. Acute vessels were evaluated for the presence of medial injury, disruption and/or dissection, whereas chronic vessels underwent morphometric analysis measuring the residual luminal area (Lumen area/Intimal area+Lumen area) and the maximal intimal thickness. Adequate adventitial penetration was confirmed by infusing as little as 2-3 ml of methylene blue at 2 atmospheres of pressure. Infusion of 3 ml of normal saline at 2 atmospheres resulted in minor focal medial edema and disorganization, detected both acutely and 14 days after porous balloon infusion. At delivery pressures of 5 or 10 atmospheres, proportionally more acute injury was noted and measurable neointimal lesions were observed 2 weeks after infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Angioplasty, Balloon, Coronary↗

PubMed1993

Okadaic acid, insulin, and denervation effects on glucose and amino acid transport and glycogen synthesis in muscle.

Effects of okadaic acid (OKA) and calyculin A, cell-permeating specific inhibitors of phosphoprotein phosphatases-1 and -2A, were studied in isolated rat hemidiaphragms. OKA stimulated glucose transport (half-maximum = approximately 0.1 microM; maximum = approximately 1 microM) but was less effective than 6 nM insulin. Insulin and OKA effects were not additive. OKA diminished or abolished glucose transport-stimulation by insulin. System A amino acid transport was also stimulated by OKA, insulin was more effective, and preexposure to OKA inhibited insulin stimulation. Calyculin A affected both transport systems similarly to OKA. OKA did not affect basal glycogen synthesis but abolished its stimulation by insulin. Denervated muscles develop post-receptor insulin resistance. Glucose transport and glycogen synthesis were essentially unresponsive to insulin 3 days postdenervation; however, glucose transport was stimulated by OKA similarly to controls. OKA did not affect glycogen synthesis in denervated muscle except for abolishing a small insulin effect. The data suggest similar acute regulation of glucose and system A amino acid transport in muscle. Enhanced Ser/Thr phosphorylation of unidentified protein(s) stimulates both processes but inhibits their full stimulation by insulin. Postdenervation insulin resistance likely reflects impaired signal transduction.

Amino Acids↗

PubMed1993

Pre-exposure to glucosamine induces insulin resistance of glucose transport and glycogen synthesis in isolated rat skeletal muscles. Study of mechanisms in muscle and in rat-1 fibroblasts overexpressing the human insulin receptor.

Increased routing of glucose through the hexosamine-biosynthetic pathway has been implicated in the development of glucose-induced insulin resistance of glucose transport in cultured adipocytes. Because both glucosamine and glucose enter this pathway as glucosamine-6-phosphate, we examined the effects of preincubation with glucosamine in isolated rat diaphragms and in fibroblasts overexpressing the human insulin receptor (HIR-cells). In muscles, pre-exposure to glucosamine inhibited subsequent basal and, to a greater extent, insulin-stimulated glucose transport in a time- and dose-dependent manner and abolished the stimulation by insulin of glycogen synthesis. Insulin receptor number, activation of the insulin receptor tyrosine kinase in situ and after solubilization, and the total pool of glucose transporters (GLUT4) were unaffected, and glycogen synthase was activated by glucosamine pretreatment. In HIR-cells, which express GLUT1 and not GLUT4, basal and insulin-stimulated glucose transport were unaffected by glucosamine, but glycogen synthesis was markedly inhibited. Insulin-stimulated activation of protein kinases (MAP and S6) was unaffected, and the fractional velocity and apparent total activity of glycogen synthase was increased in glucosamine-treated HIR-cells. In pulse-labeling studies, addition of glucosamine during the chase prolonged processing of insulin proreceptors to receptors and altered the electrophoretic mobility of proreceptors and processed alpha-subunits, consistent with altered glycosylation. Glucosamine-induced insulin resistance of glucose transport appears to be restricted to GLUT4-expressing cells, i.e., skeletal muscle and adipocytes; it may reflect impaired translocation of GLUT4 to the plasmalemma. The glucosamine-induced imbalance in UDP sugars, i.e., increased UDP-N-acetylhexosamines and decreased UDP-glucose, may alter glycosylation of critical proteins and limit the flux of glucose into glycogen.

Animals↗

PubMed1993

Discordant results for determinations of triglycerides in pig sera.

We recently determined triglyceride concentrations in pig sera by three fully enzymatic methods (Kodak Ektachem 700, Hitachi 707, and Abbott EPx) and obtained significantly lower values than those obtained with chemical or enzymatic methods based on chemical hydrolysis. All methods used involve microbial lipases for liberating glycerol from glycerides and glycerol phosphate dehydrogenases or oxidases for subsequent oxidation. The methods were validated against reference methods by using fresh human sera and survey materials. The discordant results were not from matrix sample-method interaction but from incomplete hydrolysis of pig serum triglycerides by the lipolytic enzymes. When serum triglycerides from 10 pigs showing the highest biases were hydrolyzed by microbial lipases and the reaction mixture was subjected to thin-layer and gas-liquid chromatography, the predominant end products were palmitoyl monoglyceride and a mixture of free fatty acids with the following composition (fatty acid as percent of total +/- SD): 16:0, 7.8 +/- 2; 18:0, 5.4 +/- 2.2; 18:1, 53 +/- 12; 18:2, 31 +/- 4.6; and 18:3, 2.5 +/- 1. Assuming that the lipases exhibit the usual specificity toward the 1 and 3 positions of the triglyceride, the data suggest that, in pig, triglycerides 18:1 and 18:2 occupy the 1 and 3 positions and 16:0 (palmitic acid) predominantly occupies the 2 position. Triglycerides of this structure may not be well hydrolyzed by the typical lipolytic enzymes in clinical assays.

Animals↗

PubMed1992

Coronary intimal proliferation after balloon injury and stenting in swine: an animal model of restenosis.

OBJECTIVES: This study was designed to compare the proliferative response in coronary arteries after tantalum stent placement or balloon injury in a normolipemic swine model of restenosis. BACKGROUND: Restenosis remains a significant complication of percutaneous transluminal coronary angioplasty. Efforts to study restenosis have been hampered by the lack of a suitable animal model. METHODS: In an attempt to create lesions resembling those of human restenosis, normolipemic swine underwent injury of either the left anterior descending or the left circumflex coronary artery with either balloon inflation or deployment of a tantalum stent. At 4 weeks, they were killed and the injured vessels processed for histopathologic analysis. Intimal area, lumen area and maximal intimal thickness were measured. The degree of stenosis was expressed as residual lumen area (lumen area/intimal area ratio). RESULTS: Vessels injured by either method demonstrated significant intimal smooth muscle proliferation leading to reduction in lumen area. In the 18 stented vessels residual lumen area measured 0.64 +/- 0.18 and maximal intimal thickness measured 0.6 +/- 0.3 mm; in the 15 balloon-injured vessels these values were 0.75 +/- 0.18 and 0.4 +/- 0.3 mm, respectively (p less than 0.05). In addition, most stented vessels had reactive inflammatory infiltrates surrounding the stent wires composed of lymphocytes, histiocytes and many eosinophils. CONCLUSIONS: These data indicate that coronary artery injury in swine with either balloon inflation or stenting leads to intimal smooth muscle cell proliferation similar to that seen in human restenosis. The degree of intimal proliferation appears to be greater after stenting than after balloon injury. Intracoronary stenting in swine is associated with a marked inflammatory reaction around the stent wires. These models may be helpful in planning systemic and local antirestenosis strategies.

Angioplasty, Balloon, Coronary↗

PubMed1992

Increasing resistance of enterococci to ciprofloxacin.

We determined that resistance to ciprofloxacin has emerged in enterococci over the last 5 years in our hospital, mainly in strains demonstrating the phenotype of high-level gentamicin resistance. All high-level-gentamicin-resistant isolates from 1985 and 1986 were susceptible, whereas 24% of isolates from 1989 and 1990 were resistant to ciprofloxacin. Plasmid and genomic DNA typing showed at least six unique strains exhibiting resistance, but one type accounted for 80% of recent resistant isolates, suggesting a role for cross infection in the emergence of resistance.

Ciprofloxacin↗

PubMed1992

Phosphorylation of the rodent negative acute-phase protein alpha 1-inhibitor-III by the insulin receptor tyrosine kinase.

alpha 1-Inhibitor-III (alpha 1I3), a broad range proteinase inhibitor, member of the alpha-macroglobulin family, is abundant in normal rat plasma. Insulin-dependent tyrosine phosphorylation of a monomeric 195K glycoprotein (pp195) was observed in wheatgerm agglutinin (WGA)-Sepharose-purified insulin receptor preparations from rat liver and muscle. Phosphorylation of pp195 in vitro required a basic poly-amino acid, i.e. poly-L-lysine. We present evidence identifying pp195 as alpha 1I3. In situ perfusion with saline essentially removed pp195 from rat livers. Addition of normal rat plasma to liver homogenates or to WGA eluates restored insulin-stimulated phosphorylation of pp195; plasma from streptozotocin-diabetic rats was much less effective. Liver-derived pp195 copurified with an abundant plasma protein, with the characteristics of alpha 1I3, on size exclusion and ion-exchange chromatography. An approximately 195K protein, comigrating with alpha 1I3, was markedly diminished in plasma from diabetic rats, and alpha 1I3 concentration was decreased by approximately 70% upon immunoblot analysis. Highly purified alpha 1I3 was phosphorylated by muscle- or liver-derived insulin receptors in the presence of 1 microM poly-L-lysine and comigrated with pp195 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. alpha 1I3 phosphorylation was half-maximal at approximately 70 nM and was stimulated by insulin 7-fold. Hindlimb perfusion removed more than 90% plasma albumin but only approximately 20% pp195 from muscles. alpha 1I3 messenger RNA was identified in liver but not in muscle. A specific antibody against alpha 1I3 immunoprecipitated phosphorylated pp195 in WGA-purified insulin receptor preparations from nonperfused liver and from saline perfused and nonperfused muscle. alpha 1I3 is bound and internalized by alpha-macroglobulin receptors; whether it is phosphorylated in vivo is unknown. Hepatic alpha 1I3 synthesis may diminish in diabetic rats.

Acute-Phase Proteins↗

PubMed1991

Effects of insulin and phospholipase C in control and denervated rat skeletal muscle.

Phospholipase C (PLC), an enzyme that increases endogenous 1,2-diacylglycerol (DAG), caused dose-dependent stimulation of 2-deoxy-D-glucose (2-DG) uptake in rat soleus muscles; the maximal effect was less than that of insulin. In denervated muscles the effect of insulin on 2-DG uptake was markedly reduced, whereas the response to PLC was identical to that of control muscles. Both PLC and insulin stimulated glucose incorporation into glycogen in control but not in denervated solei. Amino acid transport was unaffected by PLC; however, the enzyme completely inhibited the stimulation of amino acid transport by insulin. PLC did not activate the insulin receptor tyrosine kinase but decreased activation of the receptor by insulin in vivo. Basal muscle DAG content increased after denervation. Incubation with PLC markedly increased DAG in control and in denervated muscle. Insulin increased total DAG mass less than PLC in control muscles and did not affect DAG in denervated muscles. In media without added Ca2+, PLC stimulation of DAG production was impaired, and 2-DG uptake was unresponsive to PLC. The data are consistent with, but do not prove, that a subpopulation of DAGs may participate in insulin-mediated stimulation of glucose transport. They also suggest that the denervation-induced insulin resistance of glucose transport may reflect impaired generation of certain DAGs involved in the signaling cascade.

Animals↗

PubMed1991

Effect of denervation on the expression of two glucose transporter isoforms in rat hindlimb muscle.

Denervation rapidly (within 24 h) induces insulin resistance of several insulin-responsive pathways in skeletal muscle, including glucose transport; resistance is usually maximal by 3 d. We examined the effect of denervation on the expression of two glucose transporter isoforms (GLUT-1 and GLUT-4) in rat hindlimb muscle; GLUT-4 is the predominant species in muscle. 1 d postdenervation, GLUT-1 and GLUT-4 mRNA and protein concentrations were unchanged. 3 and 7 d postdenervation, GLUT-4 mRNA and protein (per microgram DNA) were decreased by 50%. The minor isoform, GLUT-1 mRNA increased by approximately 500 and approximately 100%, respectively, on days 3 and 7 while GLUT-1 protein increased by approximately 60 and approximately 100%. The data suggest that the insulin resistance of glucose transport early after denervation does not reflect a decrease in total glucose transporter number; however, decreased GLUT-4 expression may contribute to its increased severity after 3 d. Parallel decreases in GLUT-4 mRNA and GLUT-4 protein postdenervation are consistent with pretranslational regulation; GLUT-1 expression may be regulated pre- and posttranslationally. The cell type(s) which overexpress GLUT-1 postdenervation need to be identified. Nervous stimuli and/or contractile activity may modulate the expression of GLUT-1 and GLUT-4 in skeletal muscle tissue.

Animals↗

PubMed1991

Diabetes-associated impairment of hepatic insulin receptor tyrosine kinase activity: a study of mechanisms.

Insulin receptor tyrosine kinase activity solubilized from liver of control and streptozotocin diabetic rats was studied using histone H2b and poly-Glu-Tyr (4:1) as phosphoacceptors. Both substrates inhibited autophosphorylation and exogenous kinase activity when added before, but not after, receptor activation with ATP. When H2b was added before ATP, insulin stimulated exogenous kinase activity of diabetic-derived receptors was significantly higher (approximately 50%) than control values at low H2b concentrations, but significantly lower (approximately 50%) than control values at high H2b concentrations, suggesting a decrease in the apparent Km and maximal velocity of the diabetic receptor tyrosine kinase toward H2b. When receptors were allowed to maximally autophosphorylate before the addition of H2b, the maximal H2b kinase activity of diabetic-derived receptors was only approximately 25% lower than that of controls. These effects were not attributable to altered ATP kinetics. Insulin receptor kinase activity toward the substrate poly-Glu-Tyr (4:1) was unaltered by insulinopenic diabetes. Insulin receptor alpha-beta dimers were not detectable in either control or diabetic-derived preparations. We conclude that the impairment of hepatic insulin receptor kinase activity associated with insulinopenic diabetes reflects a decreased ability to maximally activate, which is enhanced when the receptor is activated in the presence of some substrates, e.g. H2b. Impaired signalling by the diabetic-derived receptor appears to be dependent on the type of substrate and its concentration.

Adenosine Triphosphate↗

PubMed1991

Skeletal muscle insulin-receptor kinase. Effects of substrate inhibition and diabetes.

Insulin receptor tyrosine kinase activity solubilized from hind limb muscle of control and streptozocin-induced diabetic (STZ-D) rats (2-3 wk) was studied with the substrates histone H2B and poly glutamic acid-tyrosine (glu-tyr) (4:1). Basal and insulin-stimulated kinase activities were inhibited when high concentrations of either substrate were added before initiation of phosphorylation with ATP. Under these conditions, insulin-stimulated activities of diabetic- and control-derived receptor kinase toward H2B were similar at 0.008 mg/ml H2B. However, higher concentrations of H2B (0.04-1 mg/ml) progressively reduced the ratios of diabetic-derived to control-derived receptor kinase activities to approximately 0.5. When inhibition of receptor kinase activities was prevented by allowing maximal autophosphorylation of insulin receptors before addition of H2B, kinase activity of diabetic- and control-derived receptors was similar at all H2B concentrations. Diabetic-derived insulin-receptor tyrosine kinase activity toward poly glu-tyr (4:1) was not significantly different from that of control rats. Under conditions of substrate inhibition (0.4 mg/ml H2B), insulin receptor H2B kinase activity from muscles of rats with severe diabetes (85 mg/kg STZ, 7 days) was significantly decreased, whereas the same activity from rats with moderate diabetes (50 mg/kg STZ, 7 days) was not significantly different from control rats. Insulin receptor alpha,beta dimers were not detectable in muscle preparations from control or diabetic rats. The data suggest that the impairment of muscle-derived insulin-receptor tyrosine kinase activity associated with insulinopenic diabetes reflects, in part, enhanced inhibition by some substrates. If solubilized insulin receptors and the exogenous substrates studied model in vivo events, impaired signaling of the muscle insulin receptor in insulinopenic diabetes may depend on the type and concentration of intracellular tyrosine kinase substrates and the severity of the metabolic derangements.

Animals↗

PubMed1991

Ultrastructure of coronary arterial endothelium in atherosclerotic swine suggests lipid retro-endocytosis.

During experimental atherosclerosis, arterial endothelial cells show characteristic ultrastructural changes including the appearance of increased numbers of plasmalemmal and cytoplasmic vesicles. These structures have been shown by tracer studies to participate in the transcellular transport of low-density lipoprotein cholesterol and beta-very-low-density lipoprotein cholesterol from the arterial lumen into the abluminal extracellular matrix. Although this probably represents the major lipid transport pathway, other forms of transport may exist. We document the presence of apparent lipid structures averaging approximately 300 nm in diameter at or near the luminal surface of coronary arterial endothelium of atherosclerotic miniature swine. The structures exhibited a particulate nature with subunits of a heterogenous size distribution. The appearance of the endothelial plasmalemma adjacent and subjacent to these structures suggests exocytosis. We hypothesize that this previously unreported morphology may represent an in vivo structural correlate for the lipoprotein retro-endocytosis pathway which has been recently identified using biochemical methods in smooth muscle cells and fibroblasts in vitro.

Animals↗