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PubMed1990

The effect of inhibitors of glycoprotein synthesis and processing on the phagocytosis of rod outer segments by cultured retinal pigment epithelial cells.

Retinal pigment epithelial cells selectively phagocytize rod outer segments by a process that may be mediated by specific cell surface receptors. Since many receptors are glycoproteins, we have studied the effect of tunicamycin, an inhibitor of N-linked oligosaccharide synthesis, and of castanospermine and swainsonine, which are inhibitors of oligosaccharide processing, on the ability of cultured retinal pigment epithelial cells to phagocytize rod outer segment. Tunicamycin inhibits the glycosylation of newly synthesized glycoproteins by 85-90%; concomitantly, the phagocytosis of rod outer segments is inhibited by 70-80%. The effect of tunicamycin is to initially reduce rod outer segments binding, and therefore the subsequent ingestion of rod outer segments. SDS-PAGE analysis and autoradiography of [35S]methionine labelled extracts of tunicamycin-treated cells, demonstrates the disappearance of a number of glycoprotein bands, and the appearance of a number of protein bands of lower Mr. Kinetic analysis of the disappearance and reappearance of specific glycoproteins suggests that the lower Mr bands are the non-glycosylated forms of the higher Mr bands. By contrast, castanospermine and swainsonine have no effect on the ability of retinal pigment epithelial cells to phagocytize rod outer segments, or on the SDS-PAGE pattern of treated cells, although they were shown to inhibit oligosaccharide processing as expected. These results support the hypothesis that rod outer segment phagocytosis by retinal pigment epithelial cells is mediated by specific glycoprotein receptors. N-Glycosylation of these receptors is required for their function, or for their insertion into the plasma membrane, whereas processing of the N-linked oligosaccharide chains of these receptors is not crucial for rod outer segment phagocytosis by retinal pigment epithelial cells.

Animals↗

PubMed2003

Pathology of minimal change nephropathy and segmental sclerosing glomerular disorders.

Minimal change nephropathy is relatively uncontroversial. This can be defined as the condition associated with the nephrotic syndrome in which glomeruli have no abnormality on light microscopy. Segmental sclerosing glomerular disorders are often called focal segmental glomerulosclerosis, one of the most controversial terms in kidney disease. The tubular opening is the earliest site at which segmental changes appear. These tip changes are not a disease in themselves. The glomerular tip lesion has tip changes in otherwise normal glomeruli. Tip changes in large glomeruli with mesangial increase can be called early classical segmental sclerosing disease. This can progress to give abnormalities at various sites, or late classical segmental sclerosing disease, corresponding with the classical descriptions of focal segmental glomerulosclerosis. Hilar abnormalities are a characteristic finding in reduced glomerular numbers. Focal segmental glomerulosclerosis is an ambiguous term, applied to many different types of segmental sclerosing glomerular disorders.

Glomerulosclerosis, Focal Segmental↗

PubMed1996

CD36 participates in the phagocytosis of rod outer segments by retinal pigment epithelium.

Mechanisms of phagocytosis are complex and incompletely understood. The retinal pigment epithelium provides an ideal system to study the specific aspects of phagocytosis since an important function of this cell is the ingestion of packets of membranous discs that are normally discarded at the apical ends of rod and cone cells during outer segment renewal. Here we provide evidence that rod outer segment phagocytosis by retinal pigment epithelium is mediated by CD36, a transmembrane glycoprotein which has been previously characterized on hematopoietic cells as a receptor for apoptotic neutrophils and oxidized low density lipoprotein. Immunocytochemical staining with monoclonal and polyclonal antibodies demonstrated CD36 expression by both human and rat retinal pigment epithelium in transverse cryostat sections of normal retina and in primary cultured cells. By western blot analysis of retinal pigment epithelial cell lysates, polyclonal and monoclonal antibodies to CD36 recognized an 88 kDa protein which comigrated with platelet CD36. Furthermore, the synthesis of CD36 mRNA by retinal pigment epithelium was confirmed by reverse transcriptase-PCR using specific CD36 oligonucleotides. The addition of CD36 antibodies to cultured retinal pigment epithelial cells reduced the binding and internalization of 125I-labeled rod outer segments by 60%. Immunofluorescence confocal microscopy confirmed that outer segment uptake was significantly diminished by an antibody to CD36. Moreover, we found that transfection of a human melanoma cell line with CD36 cDNA enabled these cells to bind and internalize isolated photoreceptor outer segments as seen by double immunofluorescent staining for surface bound and total cell-associated rod outer segments, and by measurement of cell-associated 125I-labeled rod outer segments. We conclude that the multifunctional scavenger receptor CD36 participates in the clearance of photoreceptor outer segments by retinal pigment epithelium and thus, participates in the visual process.

Aged↗

PubMed2006

All-trans retinol in rod photoreceptor outer segments moves unrestrictedly by passive diffusion.

The visual pigment protein of vertebrate rod photoreceptors, rhodopsin, contains an 11-cis retinyl moiety that is isomerized to all-trans upon light absorption. Subsequently, all-trans retinal is released from the protein and reduced to all-trans retinol, the first step in the recycling of rhodopsin's chromophore group through the series of reactions that constitute the visual cycle. The concentration of all-trans retinol in photoreceptor outer segments can be monitored from its fluorescence. We have used two-photon excitation (720 nm) of retinol fluorescence and fluorescence recovery after photobleaching to characterize the mobility of all-trans retinol in frog photoreceptor outer segments. Retinol produced after rhodopsin bleaching moved laterally in the disk membrane bilayer with an apparent diffusion coefficient of 2.5 +/- 0.3 micro m(2) s(-1). The diffusion coefficient of exogenously added retinol was 3.2 +/- 0.5 micro m(2) s(-1). These diffusion coefficients are in close agreement with those reported for lipids, suggesting that retinol is not tightly bound to protein sites that would be diffusing much more slowly in the plane of the membrane. In agreement with this interpretation, a fluorescent-labeled C-16 fatty acid diffused laterally with a similar diffusion coefficient, 2.2 +/- 0.2 micro m(2) s(-1). Retinol also moved along the length of the rod outer segment, with an apparent diffusion coefficient of 0.07 +/- 0.01 micro m(2) s(-1), again suggesting that it is not tightly bound to proteins that would confine it to the disks. The axial diffusion coefficient of exogenously added retinol was 0.05 +/- 0.01 micro m(2) s(-1). In agreement with passive diffusion, the rate of axial movement was inversely proportional to the square of the length of the rod outer segment. Diffusion of retinol on the plasma membrane of the outer segment can readily account for the measured value of the axial diffusion coefficient, as the plasma membrane comprises approximately 1% of the total outer-segment membrane. The values of both the lateral and axial diffusion coefficients are consistent with most of the all-trans retinol in the outer segments moving unrestricted and not being bound to carrier proteins. Therefore, and in contrast to other steps of the visual cycle, there does not appear to be any specialized processing for all-trans retinol within the rod outer segment.

Animals↗

PubMed1996

Photoreceptor repair in response to RPE transplants in RCS rats: outer segment regeneration.

PURPOSE: We have previously shown that transplants of normal rat neonatal RPE cells rescued photoreceptor cells in retinas of Royal College of Surgeons (RCS) dystrophic rats for up to one year. In this study, we investigated the photoreceptor rescue effects in RCS rats within the first three weeks following transplantation in an attempt to determine if RPE transplants initiate repair mechanisms, specifically, outer segment (OS) regeneration. METHODS: Freshly isolated RPE cells from neonatal pigmented Long Evans rats were transplanted into the subretinal space of 22-23 day-old RCS rats using a transscleral approach. For controls, vehicle was similarly injected. RESULTS: When analyzed at 10 days post-transplantation, long inner segments were observed with short buds of outer segment growth in the area of the RPE-cell transplants. The outer segments were of insufficient length to be measured at 10 days, but by 14 and 21 days, OS were 2.02 +/- 0.32 microns and 18.80 +/- 2.78 microns, respectively. In vehicle-injected retinas from 10 to 21 days postsurgery, outer segments were not observed and the inner segments were three-fold shorter than in RPE-transplanted retinas. At 10 days post-transplantation, most RPE cells were seen in the subretinal space, but a few had attached to Bruch's membrane; however, by 21 days, many of the transplanted RPE cells had attached to Bruch's membrane, although a few were found free in the subretinal space. CONCLUSIONS: This study has shown that transplants of normal rat neonatal RPE cells have the capacity to support not only photoreceptor cell survival but also initiate early repair mechanisms as exhibited by outer segment regeneration in RCS retinas. These results also conclusively show the important role that the RPE plays in outer segment growth and maturation.

Animals↗

PubMed1991

Glycolytic enzymes and a GLUT-1 glucose transporter in the outer segments of rod and cone photoreceptor cells.

The presence of glycolytic enzymes and a GLUT-1-type glucose transporter in rod and cone outer segments was determined by enzyme activity assays, glucose uptake measurements, Western blotting, and immunofluorescence microscopy. Enzyme activities of six glycolytic enzymes including hexokinase, phosphofructokinase, aldolase, glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate kinase, pyruvate kinase, and lactate dehydrogenase, were found to be present in purified rod outer segment (ROS) preparations. Immunofluorescence microscopy of bovine and chicken retina sections labeled with monoclonal antibodies against glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate kinase, and lactate dehydrogenase have confirmed that these enzymes are present in rod and cone outer segments and not simply contaminants from the inner segments or other cells. Rod outer segments were also found to contain glucose transport activity as detected by 3-O-[14C]methylglucose uptake and exchange. The glucose transporter had a Km of 6.3 mM and a Vmax of 0.15 nmol of 3-O-methylglucose/s/mg of ROS membrane protein for net uptake and a Km of 29 mM and a Vmax of 1.06 nmol of 3-O-methylglucose/s/mg of ROS membrane protein for equilibrium exchange. These Km values for net uptake and equilibrium exchange are similar to values obtained for human red blood cells and are characteristic of GLUT-1-type glucose transporter. The transport was inhibited by both cytochalasin B and phloretin. Western blot analysis and immunofluorescence microscopy using type-specific glucose transporter antibodies indicated that both rod and cone outer segment plasma membranes have a GLUT-1 glucose transporter of Mr 45K as found in red blood cells and brain microsomal membranes. Solid-phase radioimmune competitive inhibition studies indicated that rod outer segment plasma membranes contained 15% the number of glucose transporters found in human red blood cell membranes and had an estimated density of 400 glucose transporter per micron2 of plasma membrane. These studies support the view that outer segments can generate energy in the form of ATP and GTP by anaerobic glycolysis to supply at least some of the energy requirements for phototransduction and other metabolic processes.

3-O-Methylglucose↗

PubMed1990

Glyceraldehyde-3-phosphate dehydrogenase is a major protein associated with the plasma membrane of retinal photoreceptor outer segments.

A major 38-kDa protein associated with bovine rod outer segment plasma membranes, but not disk membranes, has been identified as glyceraldehyde-3-phosphate dehydrogenase on the basis of its N-terminal sequence and specific enzyme activity. This enzyme was extracted from lysed rod outer segments or isolated rod outer segment plasma membrane with 0.15 M NaCl and purified to homogeneity by affinity chromatography on a NAD(+)-agarose column. A specific activity of 90-100 units/mg of protein is within the range of activity obtained for glyceraldehyde-3-phosphate dehydrogenase isolated from other mammalian cells. Enzyme activity measurements indicate that this enzyme makes up approximately 2% of the total rod outer segment protein and over 11% of the plasma membrane protein. Protease digestion and binding studies on purified rod outer segment plasma and disk membranes suggest that glyceraldehyde-3-phosphate dehydrogenase reversibly interacts with a protease-sensitive plasma membrane-specific protein of rod outer segments. The finding that glyceraldehyde-3-phosphate dehydrogenase is present in large quantities in rod outer segments suggests that at least some of the energy required for the synthesis of ATP and GTP for phototransduction and other processes of the outer segment is derived from glycolysis which takes place within this organelle.

Amino Acid Sequence↗

PubMed1988

A diurnal rhythm in opsin content of Rana pipiens rod inner segments.

Quantitative electron microscope immunocytochemistry, employing an antibody specific to opsin, was used to evaluate the amount and location of opsin in Rana pipiens rod photoreceptors throughout a 24 hr light/dark cycle. We found a distinct diurnal rhythm in the density of anti-opsin labeling of the rough endoplasmic reticulum (RER) and Golgi apparatus in the myoid region of the rod inner segment. Opsin labeling of these organelles was lowest at light onset, increasing thereafter by three- to four-fold, and remained high until 2 hr into the dark phase. A fall in labeling density occurred within the following 4 hr, and remained low for the remainder of the dark phase. Our finding of a diurnal rhythm regulating inner segment opsin transport in Rana pipiens contrasts with published observations on outer segment membrane turnover, since it has been shown that the rates of disc formation and disc shedding are governed by environmental lighting alone in this species. These results imply that there is opsin pooling in the inner segment during the first 14 hr of a 24 hr light/dark cycle; thereafter the loss of inner segment opsin due to mobilization of this protein from the Golgi exceeds the rate of formation of new opsin. There was no evidence of accumulation of opsin-containing vesicles near the cilium or in the ellipsoid just prior to light onset. At light onset, prominent opsin labeling was identified at the proximal portion of the outer segment in regions separate from the disc stack. In two separate experiments, additional groups of frogs were killed around the time of light onset and were examined by conventional transmission electron microscopy. Disordered disc membranes were seen at the base of the outer segment which were not in register with the disc stack. These disordered membranes were observed as early as 2 hr before light onset, and were no longer observed by 1 hr after light onset. We suggest that these disordered membranes reflect a step in the biogenesis of new discs, serving as a pool of membrane that forms during the later part of the dark cycle. It appears that light onset triggers the ordering of neatly registered discs from this new membrane, rather than assembly of new membrane from pooled transport vesicles in the inner segment.

Animals↗

PubMed1978

Focal segmental sclerosis or scarred focal proliferative glomerulonephritis?

We have made a blind retrospective analysis of 334 renal biopsies, each containing more than 10 glomeruli, from adults and children with glomerulonephritis, in order to assess the clinicopathological significance of segmental lesions. These were defined as endocapillary proliferation and/or sclerosis involving capillary loops, and a less than half the glomerular tufts. On optical microscopy of paraffin-embedded material, 57 biopsies containing segmental lesions were independently classified by two observes as "focal proliferative glomerulonephritis" or "focal segmental glomerulosclerosis". These results were then reviewed with immunofluorescence, electron microscopic and clinical data and an "executive" diagnosis reached. Scarred focal proliferative glomerulonephritis could not be reliably distinguished from focal segmental glomerulosclerosis by optical microscopy alone. Some cases of focal proliferative glomerulonephritis are not associated with systemic disease and may have negative immunofluorescence findings, and we were unable to distinguish scarring in these patients from the lesion of focal segmental glomerulosclerosis with any of the tools at our disposal. Some patients with scarred focal proliferative glomerulonephritis showed profuse proteinuria, a nephrotic syndrome and progression to renal insufficiency. These cases cannot therefore be differentiated from focal segmental glomerulosclerosis by their clinical features. It would seem that the morphological lesion of focal segmental glomerulosclerosis should be regarded as focal segmental glomerular scarring from a variety of insults, rather than a distinct disease entity.

Adolescent↗

PubMed1994

Glucose metabolism in photoreceptor outer segments. Its role in phototransduction and in NADPH-requiring reactions.

Glucose metabolism in the photoreceptor rod outer segment produces both ATP (GTP) and NADPH to support phototransduction and NADPH-requiring processes in this organelle. Glycolysis in isolated bovine rod outer segments produces 44.0 +/- 6.4 nmol of ATP/min/mg of protein or 5.7 mM ATP/min. This rate of ATP production is more than sufficient to maintain the basal rate of cGMP synthesis (0.86 mM cGMP/min) in the dark requiring 1.7 mM ATP/min. Following photoexcitation, the 4.5-fold increase in the turnover of cGMP requires an ATP synthesis rate of up to 7.7 mM ATP/min (Ames, A., Walseth, T. F., Heyman, R. A., Barad, M., Graeff, R. M., and Goldberg, N. D. (1986) J. Biol. Chem. 261, 13034-13042). Under these conditions the rate of ATP production by glycolysis as measured in isolated rod outer segments is not sufficient for the regeneration of cGMP. Additional energy is most likely provided by the phosphocreatine shuttle which transports high energy phosphate groups in the form of creatine phosphate from the rod inner segment to the rod outer segment for conversion to ATP. The hexose monophosphate pathway in bovine rod outer segments can produce up to 39.8 +/- 2.2 nmol of NADPH/min/mg of protein. This rate of NADPH production is sufficient to support both the reduction of retinal to retinol (1.2 +/- 0.2 nmol of NADPH/min/mg of protein) following the photobleaching of rhodopsin and glutathione reduction (1.1 +/- 0.1 nmol of NADPH/min/mg of protein) for the protection of rod outer segments from oxidative damage. These studies provide insight into the contribution of anaerobic glycolysis and the hexose monophosphate pathway in providing energy and nucleotides for phototransduction and other outer segment processes.

Adenosine Triphosphate↗

PubMed1993

Manometry of individual segments of the distal esophageal sphincter. Its relation to functional incompetence.

The major components of the lower esophageal sphincter, the pressure it exerts, its total length, and the length of sphincter affected by abdominal pressure are usually expressed as means of several recordings from different radial segments of the sphincter. In segmental manometry, the individual readings for these components in each segment, rather than the mean values, are analyzed. We used segmental manometry to study 50 normal volunteers and 200 patients with symptoms suggestive of gastroesophageal reflux. Of the latter, 100 had increased esophageal acid exposure and 100 did not. An increased number of defective segments was associated with a greater prevalence of increased esophageal acid exposure. Segmental analysis disclosed the same number (52) of defective sphincters (defined as sphincters with two or more defective segments) in the 100 patients with increased acid exposure as did standard analysis. However, the relationship between a defective lower esophageal sphincter and the number of reflux episodes was clearer when a defective sphincter was defined using standard analysis. Segmental analysis of the lower esophageal sphincter has no clear advantage over standard analysis.

Adolescent↗

PubMed1996

Nuclear and cellular size of myocytes in different segments of the developing rat heart.

BACKGROUND: In the embryonic heart, the individual cardiac segments show different growth rates. For the analysis of changing form in relation with changing function, data on number and shape of cardiomyocytes are necessary. Such data will give insight into the process of hypertrophy and/or hyperplasia as they may take place in the myocardium in the embryonic period. METHODS: We have measured the volumes of the nuclei and myocytes as well as the surface areas of the nuclear envelope and cellular membrane using stereological tools in rat embryos from 11 days postcoitum to 17 days postcoitum. From the data of the cellular volume of the myocytes and the myocardial volume of the individual segments, we have calculated the total number of myocytes during the developmental period. RESULTS: It is shown that the sinus venosus, sinu-atrial junction, and atrium increase their cellular volume during development, whereas the other cardiac segments show no difference in cellular volume. Similarly, the surface area of the cell membrane of the sinus venosus and sinu-atrial junction had increased during development. The nuclear volume and the surface area of the nuclear envelope did not differ during the period studied. The total number of myocytes showed a conspicuously smaller increase in the atrio-ventricular canal and distal outlet segment than in the other segments. CONCLUSIONS: The increase of the cellular volume in the segments sinus venosus and sinu-atrial junction seems to be due to a late differentiation process. In general, however, the increase of the myocardial volume in the individual cardiac segments is caused by hyperplasia of the cardiomyocytes in these segments and not by hypertrophy. The surface area of cells has a fixed relationship with cell volume, indicating that no important changes take place in the developmental period studied.

Age Factors↗

PubMed1998

The influence of the resolution of reciprocal ST segment changes on in-hospital complications of acute myocardial infarction after percutaneous coronary angioplasty.

We studied 120 patients (M:F 105:15, mean age 57.5 +/- 10.1 years) with acute myocardial infarction (MI) successfully treated with percutaneous coronary angioplasty (PTCA) to analyze the influence of the resolution of the ST segment elevation and depression after intervention to 1 month composite endpoints of reinfarction or reocclusion, development of congestive heart failure (CF) and death. Sum of preintervention and postintervention ST segment elevation and depression and the rate of resolution of these ST segment elevations and depressions were recorded for every patient. A total of 17 (14.2%) composite endpoint events (events group) were recorded (7 reocclusion or recurrent MI, 9 CF, and 1 death). On univariate analysis, events group patients were older (53.3 +/- 9.9 vs. 58.8 +/- 9.1 years, P = 0.032), had lesser resolution of ST segment elevations (85 +/- 24% vs. 44 +/- 55%, P = 0.017) and depression (72 +/- 26% vs. 52 +/- 30%, P = 0.009), had greater preintervention ST segment elevation (17.49 +/- 12.95 mm vs. 28.38 +/- 20.41 mm, P = 0.045), had lower ejection fraction (59.3 +/- 10.2% vs. 43.6 +/- 9.4%, P < 0.001), and had more frequent multivessel disease (71% vs. 47%, P = 0.048) compared to the nonevents group. Time from angina to reperfusion, residual stenosis, sex, infarct location and infarct-related vessel distribution were similar. On multivariate analysis (logistic regression with backward likelihood ratio) only older age (P = 0.0752), lesser rate of resolution of ST segment depression (P = 0.0262) and lower ejection fractions (P = 0.0014) were retained as predictors of the composite endpoints. Relative risk conferred by less than 50% resolution of ST segment depressions for composite endpoints were 3.78 (95% CI 1.63-8.73). We conclude that the lack of resolution of the sum of reciprocal ST segment depressions identifies a subgroup of acute MI patients with greater morbidity after primary PTCA.

Angioplasty, Balloon, Coronary↗

PubMed1997

The effect of hard segment size on the hydrolytic stability of polyether-urea-urethanes when exposed to cholesterol esterase.

Previous studies have shown that both polyester and polyether-based polyurea-urethanes are susceptible to cleavage by hydrolytic enzymes. Furthermore, it has been hypothesized that the degree of hard segment micro-domain formation in polyurethane materials, as well as its structure, influences the ability of enzymes to degrade the polymers. The current study has investigated a series of segmented polyether-urea-urethanes synthesized with the same reagents but having different hard segment content. Using these materials, the relationship between the formation of hard segment domains and the hydrolysis of urea/urethane groups was specifically addressed. Both differential scanning calorimetry and X-ray photo-electron spectroscopy data indicated that the three materials differed significantly in the extent of hard segment domain formation and the nature of the chemical groups located in the top 10 nm of the surface. Biodegradation studies showed a strong dependence on hard segment domain formation and indicated that the polymer containing the highest number of hydrolytically labile urea and urethane bonds exhibited the least degradation. The ability of a polyurethane material to form hard segment micro-domains may contribute to the formation of a protective structure for the hydrolysable hard segment linkages located within the micro-domains.

Biocompatible Materials↗

PubMed1999

Identification of segments VI and VII of the liver based on the ramification patterns of the intrahepatic portal and hepatic veins.

We describe the pattern of intrahepatic vessel ramification in the right posterior hepatic sector in a population of 197 adults. Each specimen was dissected from its visceral (inferior) surface in order to demonstrate variations in the distribution of the portal vein branches to the hepatic segments of the right lobe, especially to segments VI (S6) and VII (S7) as described by Couinaud. We also examine whether three hepatic veins, i.e., the right hepatic vein (RHV), middle hepatic vein (MHV), and the short hepatic vein (SHV), aid the identification of segmental portal branches in the lower posterior sector. Four major patterns of branching of the posterior sectorial trunk of the portal vein system are described. In group A (32.0%) a single posterior trunk formed an arch-like pattern sending multiple branches to S6 and S7 (P6 and P7). We named the multiple branches to the apparent S6 the inferoposterior portal branches. It was difficult to identify which of these branches were equivalent to P6. In group B (27.9%), the posterior sectorial trunk bifurcated to form P6 and P7. In most of the specimens in this group, therefore, we were able clearly to identify both S6 and S7 based on the portal vein system. In group C (6.6%), the trunk trifurcated to form P6, P7, and an intermediate branch, which supplied both segments or a gray zone between them. Group D (33.5%) included variations of the anterior segmental branches, and in specimens of this group, the anteromedial border of the sector was difficult to identify. Notably, the three-dimensional interdigitating topographical relationship of the hepatic veins and the portal branches was not evident in the lower posterior sector, since tributaries of the RHV and the portal branches followed similar courses and paralleled each other in the region and since the territory of the SHV was usually restricted to the superficial parenchyma near the inferior surface. In group A, tributaries of the RHV/SHV (>3 mm in diameter) passed between the inferoposterior portal branches in only 22.2%/14.3% of the specimens. Thus the hepatic veins often did not reveal which of the multiple inferoposterior branches was P6. Moreover, in the subset of Group B in which the segments were identified based on the portal vein ramification, tributaries of the RHV/SHV (>3 mm in diameter) showed the intersegmental interdigitating arrangement in only 32.0%/6.0% of the specimens. In addition, a thick tributary of the MHV, sometimes arising from S6, did not run along, but penetrated the S5/S6 border plane from the lateral to the medial side. Therefore, the three hepatic veins (RHV, SHV, MHV) often did not aid the identification of the liver segments in the region. Consequently, the less than ideal combinations of irregular configurations of the portal and hepatic venous systems suggest that the right posterior segments cannot be conclusively identified anatomically in 30-40% of cases. Other means of identification, such as the conventional proportional manner (the upper and lower halves of the posterior sector roughly correspond to S6 and S7) may be required.

Adult↗

PubMed1998

Zebrafish segmentation and pair-rule patterning.

Segmentation in the vertebrate embryo is evident within the paraxial mesoderm in the form of somites, which are repeated structures that give rise to the vertebrae and muscle of the trunk and tail. In the zebrafish, our genetic screen identified two groups of mutants that affect somite formation and pattern. Mutations of one class, the fss-type mutants, disrupt the formation of the anterior-posterior somite boundaries during somitogenesis. However, segmentation within the paraxial mesoderm is not completely eliminated in these mutants. Irregular somite boundaries form later during embryogenesis and, strikingly, the vertebrae are not fused. Here, we show that formation of the irregular somite boundaries in these mutants is dependent upon the activity of a second group of genes, the you-type genes, which include sonic you, the zebrafish homologue of the Drosophila segment polarity gene, sonic hedgehog. Further to characterize the defects caused by the fss-type mutations, we examined their effects on the expression of her1, a zebrafish homologue of the Drosophila pair-rule gene hairy. In wild-type embryos, her1 is expressed in a dynamic, repeating pattern, remarkably similar to that of its Drosophila and Tribolium counterparts, suggesting that a pair-rule mechanism also functions in the segmentation of the vertebrate paraxial mesoderm. We have found that the fss-type mutants have abnormal pair-rule patterning. Although a her1 mutant could not be identified, analysis of a double mutant that abolishes most her1 expression suggests that a her1 mutant may not display a pair-rule phenotype analogous to the hairy phenotype observed in Drosophila. Cumulatively, our data indicate that zebrafish homologues of both the Drosophila segment polarity genes and pair-rule genes are involved in segmenting the paraxial mesoderm. However, both the relationship between these two groups of genes within the genetic heirarchy governing segmentation and the precise roles that they play during segmentation likely differ significantly between the two organisms.

Animals↗

PubMed1999

Segmented k-space fast cardiac imaging using an echo-train readout.

A segmented k-space fast gradient-echo pulse sequence with an echo-train readout (FGRE-ET) was developed for high-quality cine imaging of the heart in reduced scan times. Using segmented FGRE-ET, cine images of the heart can be acquired in as few as 1-5 heart beats and do not display the geometric distortion and flow-related artifacts typically associated with cardiac echoplanar imaging (EPI). Segmented FGRE-ET was compared with conventional segmented FGRE and with conventional multi-phase EPI in normal volunteers. Segmented FGRE-ET was found to have reduced temporal blurring compared with segmented FGRE for cine imaging in 4 heart beats (P<0.05). Also, segmented FGRE-ET did not display geometric distortion characteristic of conventional EPI (P<0.05). Segmented FGRE-ET may be particularly applicable to functional cardiac stress testing because it allows versatile cine imaging in very short breath-holds.

Analysis of Variance↗

PubMed2001

Perfusion of myocardial segments of the right ventricle: role of the left coronary artery in infarction of the right ventricle.

In a series of 88 human hearts, from individuals aged between 24 h and 94 yr (x= 61.09 +/- 21.96), the coronary arterial distribution of the right ventricle was studied using a modified Selvester's system of segmentation. Postmortem angiographies and microdissection techniques were used. The analysis of the six segments of the right ventricle shows that the three anterior segments, basal, mesial, and--less frequently--apical, present a type of irrigation that is practically constant and is dual. The postero-basal and postero-mesial segments are irrigated almost exclusively by the right coronary artery. In the remaining segments the vascularization was of mixed type, although a considerable degree of exclusive arterial perfusion was observed in the antero-apical segment. The segmental analysis allows us to conclude that although arterial vascularization of the right ventricle depends fundamentally on the right coronary artery, the anterior interventricular artery irrigates more than 20% of the right ventricular myocardium. Results from segmental analysis are compared with data from clinical and necropsic studies.

Adult↗