Intrinsic cell rheology drives junction maturation

A fundamental property of higher eukaryotes that underpins their evolutionary success is stable cell-cell cohesion. Yet, how intrinsic cell rheology and stiffness contributes to junction stabilization and maturation is poorly understood. We demonstrate that localized modulation of cell rheology governs the transition of a slack, undulated cell-cell contact (weak adhesion) to a mature, straight junction (optimal adhesion). Cell pairs confined on different geometries have heterogeneous elasticity maps and control their own intrinsic rheology co-ordinately. More compliant cell pairs grown on circles have slack contacts, while stiffer triangular cell pairs favour straight junctions with flanking contractile thin bundles. Counter-intuitively, straighter cell-cell contacts have reduced receptor density and less dynamic junctional actin, suggesting an unusual adaptive mechano-response to stabilize cell-cell adhesion. Our modelling informs that slack junctions arise from failure of circular cell pairs to increase their own intrinsic stiffness and resist the pressures from the neighbouring cell. The inability to form a straight junction can be reversed by increasing mechanical stress artificially on stiffer substrates. Our data inform on the minimal intrinsic rheology to generate a mature junction and provide a springboard towards understanding elements governing tissue-level mechanics.

Impedance measurements and connexin expression in human detrusor muscle from stable and unstable bladders

Three of this month's Scientific Discovery papers highlight the importance of collaboration in delivering high quality scientific research. As scientific technology increases in power and cost, and specific areas of interest become more specialized, it is becoming more difficult to cover all aspects of a completeresearch story. Collaborating with other experts in the field or other fields, including industry, allows strong scientific proof to be generated for the hypothesis and aims. Building strong collaborative,inter-disciplinary, multi-institutional, international groups with academic and industrial partners is the way forward for all discovery. We look forward to publishing more of these collaborative papersin future issues of the BJU International.

OBJECTIVES

To test the hypothesis that intercellular electrical coupling is altered in human detrusor smooth muscle from patients with unstable bladders.

MATERIALS AND METHODS

Human detrusor biopsy samples were obtained from patients with stable and unstable bladders. Intracellular electrical impedance was measured with alternating current (20 Hz-300 kHz) across the ends of detrusor strips in an oil-gap, after correcting for extracellular space resistance. Gap junctions were identified by localization of connexins (Cx), specifically Cx45, Cx43 and Cx40 transcripts, using immunoconfocal microscopy.

RESULTS

Total intracellular resistivity was greater in strips from unstable than from stable bladders (median 1246 vs 817 Omega.cm). The increase was attributed to an increase in junctional resistance; cytoplasmic resistance was unchanged. Cx43 was localized to a submucosal layer and to connective tissue; Cx40 label was confined to endothelial cells of blood vessels. Cx45 labelling was localized to detrusor bundles and appeared to be less marked in samples from unstable bladders. Semi-quantitative analysis of Northern blots showed that Cx45 expression in unstable was less than that in stable bladders.

CONCLUSIONS

These data suggest that intercellular coupling is reduced in detrusor from unstable bladders. Cx45 was localized to the detrusor layer, with Cx 43 more evident in the suburothelial mucosa. Cx45 labelling was less intense in detrusor samples from unstable bladders. These results are consistent with reduced gap junction coupling in detrusor from unstable bladders.

Gap junctions and connexin expression in human suburothelial interstitial cells

OBJECTIVE

To determine whether suburothelial interstitial cells of the human bladder express gap junctions, and if so, to establish their extent and composition, using immunocytochemistry, confocal microscopy and electron microscopy.

MATERIALS AND METHODS

Bladder tissue was obtained at cystectomy; the tissue was: (i) frozen for cryosectioning and Northern blot analysis; (ii) fixed and embedded for standard thin-section electron microscopy; and (iii) processed using low-denaturation conditions in Lowicryl for immunogold-label electron microscopy. Cryosections were immunofluorescently labelled using antibodies against connexins 43, 40 and 45, vimentin, desmin and c-Kit ligand, and examined by confocal microscopy. Double labelling was used to determine the spatial relationship of labelling for connexin43 with that of vimentin and desmin. Thin-section electron microscopy was used to investigate interstitial cell ultrastructure and permit unequivocal identification of gap junctions, and immunogold labelling of Lowicryl sections was applied to localize connexin43.

RESULTS

Immunoconfocal microscopy showed prominent labelling for the gap junction protein, connexin43, in a suburothelial band of cells that was also strongly positive for vimentin. The connexin43/vimentin-positive cells showed only weak labelling for desmin and c-Kit ligand, and were immunonegative for connexins 40 and 45. Northern blotting showed a corresponding abundance of connexin43 transcript in the mucosal layer but not the detrusor layer of the bladder wall. Electron microscopy revealed abundant gap junctions, recognized by their pentalaminar structure, between the cell processes of interstitial cells in the suburothelial zone. That these interstitial cell gap junctions were the source of the connexin43 immunolabelling observed by immunoconfocal microscopy was confirmed by immunogold labelling in sections of Lowicryl-embedded tissue examined by electron microscopy.

CONCLUSION

A network of interstitial cells, extensively linked by connexin43-containing gap junctions, is located beneath the urothelium in human bladder. As gap junctions provide pathways for direct cell-to-cell communication, the interstitial cellular network may operate as a functional syncytium, integrating signals and responses in the bladder wall.

Multiple connexins localized to individual gap-junctional plaques in human myometrial smooth muscle

The synchronous contractions of the uterus in labour depend on electrical coupling of myometrial smooth muscle cells by gap junctions. In the human myometrium, gap junctions are scarce in the non-pregnant uterus, but become abundant at term in preparation for labour. We have previously demonstrated that in the human myometrium at term, three different gap-junctional proteins are expressed, connexins 43, 45, and 40. These connexins are known to have distinctive functional capacities in in vitro expression systems but whether, in the human myometrium in vivo, they are co-assembled into the same gap junction or form different types of gap junction has previously been unclear. By applying triple immunogold labelling to sections of Lowicryl-embedded tissue for electron microscopy, together with complementary immunoconfocal microscopy, we demonstrate here that connexins 43, 45, and 40 are commonly present as mixtures within the same gap-junctional plaque. While all gap junctions contain connexin43, the relative signal for each connexin type varies between individual junctions. The presence within single gap-junctional plaques of three different connexins, each with the potential for conferring distinctive channel properties, suggests an inherent versatility for modulation of smooth muscle cell intercellular communication properties during human parturition.

Heat stress contributes to the enhancement of cardiac mitochondrial complex activity

Hyperthermic stress is known to protect against myocardial dysfunction after ischemia-reperfusion injury. It is unclear however, what energetic mechanisms are affected by the molecular adaptation to heat stress. We hypothesized that mild hyperthermic stress can increase mitochondrial respiratory enzyme activity, affording protection to mitochondrial energetics during prolonged cardiac preservation for transplantation. Rat hearts were excised after heat-stress or sham treatment and subjected to cold cardioplegic arrest and ischemia followed by reperfusion in an ex vivo perfusion system. Cardiac function, mitochondrial respiratory, and complex activities were assessed before and after ischemia. Heat shock protein (Hsp 32, 60, and 72) expression was increased in heat-stressed hearts. This was associated with increased mitochondrial complex activities in heat-stress versus sham-treated groups for complex I-V. During reperfusion, higher complex activities and respiratory control ratios were observed in heat-stressed versus sham-treated groups. Recovery of ventricular function was improved in heat-stressed hearts. Furthermore, mitochondria in reperfused heat-stressed myocardium exhibited intact membranes with packed, parallel, lamellar cristae, whereas in sham-treated myocardium, mitochondria were severely disrupted. This study provides the first evidence of heat-stress-mediated enhancement of mitochondrial energetic capacity. This is associated with increased tolerance to ischemia-reperfusion injury. Protection by heat stress against myocardial dysfunction may be partially due to enhancement of mitochondrial energetics.

Regional differentiation of desmin, connexin43, and connexin45 expression patterns in rat aortic smooth muscle

The gap-junctional protein, connexin43, is differentially expressed in vascular smooth muscle cells (SMCs) according to phenotype. Previous studies suggest that desmin-negative SMCs are characterized by high levels of connexin43, whereas desmin-positive SMCs (of a more contractile phenotype) typically have low connexin43 levels. In this study, we examine systematically the inverse relationship between connexin43 and desmin in SMCs of defined regions of the rat aortic media and determine whether additional connexin isotypes are expressed and contribute to this relationship. Immunoconfocal microscopy demonstrated that (1) the inverse relationship between connexin43 and desmin expression holds true for the media of sequential aortic zones, with 1 exception, the ascending aorta, and (2) an additional vascular connexin, connexin45, is expressed by aortic SMCs. Examination of connexin43, connexin45, and desmin expression in sequential aortic zones reveals 3 SMC subpopulations. The first, predominating in the aortic arch and thoracic aorta, is desmin negative and contains high connexin43 levels; the second, predominating in the abdominal aorta and iliac artery, is desmin positive and contains low connexin43 levels; and the third, which is restricted to the ascending aorta, is desmin positive and expresses high connexin43 levels. Connexin45 levels are high in the ascending aorta but low in the other aortic segments. In para-aortic veins, a fourth SMC subpopulation appears, one that is desmin positive and contains connexin45 but not connexin43. These results demonstrate that a diversity of connexin expression patterns characterizes distinctive subpopulations of medial SMCs in situ with a potential to contribute to regional differentiation of vascular function.

The gap-junctional protein connexin40 is elevated in patients susceptible to postoperative atrial fibrillation

BACKGROUND

Atrial fibrillation (AF), a cardiac arrhythmia arising from atrial re-entrant circuits, is a common complication after cardiac surgery, but the proarrhythmic substrate underlying the development of postoperative AF remains unclear. This study investigated the hypothesis that altered expression of connexins, the component proteins of gap junctions, is a determinant of a predisposition to AF.

METHODS AND RESULTS

The expression of the 3 atrial connexins-connexins 43, 40, and 45-was analyzed at the mRNA and protein levels by Northern and Western blotting techniques and immunoconfocal microscopy in right atrial appendages from patients with ischemic heart disease who were undergoing coronary artery bypass surgery. Twenty percent of the patients subsequently developed AF, which allowed retrospective division of the samples into 2 groups, non-AF and AF. Connexin43 and connexin45 transcript and protein levels did not differ between the groups. However, connexin40 transcript and protein were expressed at significantly higher levels in the AF group. Connexin40 protein was markedly heterogeneous in distribution.

CONCLUSIONS

Atrial myocardium susceptible to AF is distinguished from its nonsusceptible counterpart by elevated connexin40 expression. The heterogeneity of connexin distribution could give rise to different resistive properties and conduction velocities in spatially adjacent regions of tissue, which become enhanced and, hence, proarrhythmic the higher the overall level of connexin40.

Immunocytochemical analysis of connexin expression in the healthy and diseased cardiovascular system

Gap junctions play essential roles in the normal function of the heart and arteries, mediating the spread of the electrical impulse that stimulates synchronized contraction of the cardiac chambers, and contributing to co-ordination of activities between cells of the arterial wall. In common with other multicellular systems, cardiovascular tissues express multiple connexin isotypes that confer distinctive channel properties. This review highlights how state-of-the-art immunocytochemical and cellular imaging techniques, as part of a multidisciplinary approach in gap junction research, have advanced our understanding of connexin diversity in cardiovascular cell function in health and disease. In the heart, spatially defined patterns of expression of three connexin isotypes-connexin43, connexin40, and connexin45-underlie the precisely orchestrated patterns of current flow governing the normal cardiac rhythm. Derangement of gap junction organization and/or reduced expression of connexin43 are associated with arrhythmic tendency in the diseased human ventricle, and high levels of connexin40 in the atrium are associated with increased risk of developing atrial fibrillation after coronary by-pass surgery. In the major arteries, endothelial gap junctions may simultaneously express three connexin isotypes, connexin40, connexin37, and connexin43; underlying medial smooth muscle, by contrast, predominantly expresses connexin43, with connexin45 additionally expressed at restricted sites. In normal arterial smooth muscle, the abundance of connexin43 gap junctions varies according to vascular site, and shows an inverse relationship with desmin expression and positive correlation with the quantity of extracellular matrix. Increased connexin43 expression between smooth muscle cells is closely linked to phenotypic transformation in early human coronary atherosclerosis and in the response of the arterial wall to injury. Current evidence thus suggests that gap junctions in both their guises, as pathways for cell-to-cell signaling in the vessel wall and as pathways for impulse conduction in the heart, contribute to the initial pathogenesis and eventual clinical manifestation of human cardiovascular disease.

Comparison of connexin 43, 40 and 45 expression patterns in the developing human and mouse hearts

The mouse is currently widely used as a model organism in the analysis of gene function but how developmentally regulated patterns of connexin gene expression in the mouse compare with those in the human is unclear. Here we compare the patterns of connexin expression in the heart during the development of the mouse (from embryonic day 12.5 to 6 weeks postpartum) and the human (at 9 weeks gestation and adult stage). The extent of connexin43 expression in the ventricles progressively increased during development of the mouse heart. The developmental pattern of expression for connexins 40 and 45 in the mouse heart was similar, but not identical, and in the ventricles showed a progressive and preferential expression in the conduction system. In general, these dynamic changes of connexins 43, 40 and 45 during mouse cardiac development appear to be mirrored in the human.

Connexin make-up of endothelial gap junctions in the rat pulmonary artery as revealed by immunoconfocal microscopy and triple-label immunogold electron microscopy

Integration of vascular endothelial function relies on multiple signaling mechanisms, including direct cell-cell communication through gap junctions. Gap junction proteins expressed in the endothelium include connexin37, connexin40, and connexin43. To investigate whether individual endothelial cells in vivo express all three connexin types and, if so, whether multiple connexins are assembled into the same gap junction plaque, we used affinity-purified connexin-specific antibodies raised in three different species to permit multiple-label immunoconfocal and immunoelectron microscopy in the rat main pulmonary artery. Immunoconfocal microscopy showed a high incidence of co-localization between connexin43 and connexin40, but lower incidences of co-localization between connexin37 and connexin40 or connexin43. Immunoelectron microscopy revealed that 83% of gap junction profiles contained all three connexins, with the proportion of connexin40 labeling being significantly higher than that of connexin37 or connexin43. The presence of three different connexin types of distinct properties in vitro provides potential for complex regulation and functional differentiation of endothelial intercellular communication properties in vivo.

The extra- and intracellular barriers to lipid and adenovirus-mediated pulmonary gene transfer in native sheep airway epithelium

Gene transfer to the respiratory epithelium is currently suboptimal and may be helped by the identification of limiting biological barriers. We have, therefore, developed an ex vivo model which retains many of the characteristics of in vivo native airways including mucociliary clearance, mucus coverage and an intact cellular structure. Using this model we have demonstrated several barriers to gene transfer. Liposome-mediated gene transfer was inhibited by normal mucus, with removal of this layer increasing expression approximately 25-fold. In addition both liposome and adenovirus were inhibited by CF sputum. The apical membrane represented a significant barrier to both agents. Adenovirus-mediated expression could be significantly augmented by increasing contact time or by pre-treatment of tissues with a nominally calcium-free medium. The presence of these extracellular and plasma membrane barriers appeared to be the key parameters responsible for the approximately three log difference in gene expression found in vitro compared with our ex vivo model. Cytoskeletal elements and the cell cycle also influenced in vitro gene transfer, and represent further barriers which need to be overcome.

Individual gap junction plaques contain multiple connexins in arterial endothelium

Gap-junctional intercellular communication in endothelial cells is implicated in the coordination of growth, migration, and vasomotor responses. Up to 3 connexin types, connexin40 (Cx40), Cx37, and Cx43 may be expressed in vascular endothelium according to vascular site, species, and physiological conditions. To establish how these connexins are organized at the level of the individual endothelial gap junction, we used affinity-purified connexin-specific antibodies raised in 3 different species to permit double and triple immunolabeling in combination with confocal and electron microscopy. Using HeLa cells transfected with Cx37 and Cx40 for characterization, the anti-Cx37 antibody (raised in rabbit) and the anti-Cx40 antibody (raised in guinea pig) were shown to recognize single bands of 37 and 40 kDa, respectively, on Western blots and to give prominent punctate labeling at the cell borders, specifically in the corresponding transfectant. By applying these antibodies together with mouse monoclonal anti-Cx43 for double and triple immunofluorescence labeling at confocal microscopy, rat aortic and pulmonary arterial endothelia were found to express all 3 connexin types, whereas coronary artery endothelium expressed Cx40 and Cx37 but lacked Cx43. High-resolution en face confocal viewing of the aortic endothelium after double labeling demonstrated frequent colocalization of connexins, with distinct variation in the expression pattern within a given cell, where it made contact with different neighbors. Triple immunogold labeling at the electron-microscopic level revealed that aortic endothelial gap junctions commonly contain all 3 connexin types. This represents the first definitive demonstration of any cell type in vivo expressing 3 different connexins organized within the same gap-junctional plaque.

Mechanisms of acute eosinophil mobilization from the bone marrow stimulated by interleukin 5: the role of specific adhesion molecules and phosphatidylinositol 3-kinase

Mobilization of bone marrow eosinophils is a critical early step in their trafficking to the lung during allergic inflammatory reactions. We have shown previously that the cytokine interleukin (IL)-5, generated during an allergic inflammatory reaction in the guinea pig, acts systemically to mobilize eosinophils from the bone marrow. Here, we have investigated the mechanisms underlying this release process. Examination by light and electron microscopy revealed the rapid migration of eosinophils from the hematopoietic compartment and across the bone marrow sinus endothelium in response to IL-5. Using an in situ perfusion system of the guinea pig hind limb, we showed that IL-5 stimulated a dose-dependent selective release of eosinophils from the bone marrow. Eosinophils released from the bone marrow in response to IL-5 expressed increased levels of beta2 integrin and a decrease in L-selectin, but no change in alpha4 integrin levels. A beta2 integrin-blocking antibody markedly inhibited the mobilization of eosinophils from the bone marrow stimulated by IL-5. In contrast, an alpha4 integrin blocking antibody increased the rate of eosinophil mobilization induced by IL-5. In vitro we demonstrated that IL-5 stimulates the selective chemokinesis of bone marrow eosinophils, a process markedly inhibited by two structurally distinct inhibitors of phosphatidylinositol 3-kinase, wortmannin and LY294002. Wortmannin was also shown to block eosinophil release induced by IL-5 in the perfused bone marrow system. The parallel observations on the bone marrow eosinophil release process and responses in isolated eosinophils in vitro suggest that eosinophil chemokinesis is the driving force for release in vivo and that this release process is regulated by alpha4 and beta2 integrins acting in opposite directions.

Co-localization of dystrophin and beta-dystroglycan demonstrated in en face view by double immunogold labeling of freeze-fractured skeletal muscle

An absence of dystrophin causes Duchenne muscular dystrophy, but the precise mechanism underlying necrosis of the muscle cells is still unclear. Dystrophin and beta-dystroglycan are components of a complex of at least nine proteins, the dystrophin-glycoprotein complex (DGC), that links the membrane cytoskeleton to extracellular elements in skeletal and cardiac muscle. Biochemical studies indicate that dystrophin is bound to other components of the DGC via beta-dystroglycan, which suggests that the distribution of these two proteins should be almost identical. In this study, therefore, we examined the spatial relationship between dystrophin and beta-dystroglycan with a range of different imaging techniques to investigate the extent of the predicted co-localization. We used (a) double immunogold fracture-label, a freeze-fracture cytochemical technique that allows high-resolution face-on views of labeled membrane components in thin sections and in platinum-carbon replicas, (b) double immunogold labeling of cryosections and (c) confocal microscopy. Both dystrophin and beta-dystroglycan were found over the entire fiber surface and, when labeled singly, the nearest neighbor spacing of labeling sites for the two proteins was indistinguishable. With double labeling, very close co-localization could be demonstrated. The results support the conclusion that dystrophin and beta-dystroglycan directly interact at the muscle plasma membrane. (J Histochem Cytochem 46:945-953, 1998)

Structural, biochemical and functional effects of distending pressure in the human saphenous vein: implications for bypass grafting

BACKGROUND

Distension of the saphenous vein before and after coronary artery bypass grafting results in damage to mechanisms that regulate vascular tone. We have investigated the relationship between the magnitude of distending pressure and the degree of structural, biochemical and functional damage to the vessel wall.

METHODS

Vessel segments that had been distended to either 100 or 300 mmHg were set up in isolated organ baths and the function of the smooth muscle and endothelial cells examined. All segments examined were then fixed for assessment of structural damage by scanning electron microscopy and for immunocytochemical localisation of endothelial nitric oxide synthase.

RESULTS

Segments of saphenous vein distended to 100 mmHg retained their responsiveness to KCl (90 mmol/l) and phenylephrine (10(-6) mol/l), but those pressurised to 300 mmHg had significantly reduced responses to both agents. There was also a significant reduction in response to the endothelium-dependent dilators, acetylcholine (10(-10)-10(-6) mol/l) and bradykinin (10(-10)-10(-6) mol/l) in those segments distended to 300 mmHg. Quantitative studies of structural endothelial damage showed a significant loss of endothelium at 300 mmHg distension pressure. Remaining endothelial cells retained strong positive staining for endothelial nitric oxide synthase. By electron microscopic examination, those vessels distended to 100 mmHg showed lifting and rounding of individual cells, whereas segments distended to 300 mmHg revealed major areas of denuded endothelium.

CONCLUSIONS

Distension of saphenous veins to pressures equivalent to those in the systemic circulation result in structural and biochemical changes in the endothelium that are not paralleled by immediate functional vasomotor changes.

Connexin45 expression is preferentially associated with the ventricular conduction system in mouse and rat heart

Cardiac myocytes are electrically coupled by gap junctions, clusters of low-resistance intercellular channels composed of connexins. Variations in the quantities and spatial distribution of different connexin types have been implicated in regional differentiation of electrophysiological properties in the heart. Although independent studies have demonstrated that connexin43 is abundant in working ventricular myocardium and that connexin40 is preferentially expressed in the atrioventricular conduction system of a number of species, information on the spatial distribution of connexin45 in the heart is limited to data obtained using an antibody raised to a single peptide sequence. In the present study, we report on the production and characterization of a new anti-connexin45 antibody and its application to the investigation of connexin45 expression in mouse and rat myocardium. The affinity-purified antiserum, raised in guinea pig to residues 354 to 367 of human connexin45, recognized a single 45-kD band on Western blots of HeLa cells transfected to express connexin45 and gave punctate immunolabeling at the cell borders, demonstrated by freeze-fracture cytochemistry to represent gap junctions. Only low levels of connexin45 mRNA were detected on Northern blots of mouse and rat cardiac tissues, and connexin45 protein levels were below the limit of detection on Western blots. Confocal microscopy of immunolabeled ventricular tissue revealed that the major part of the working myocardium was immunonegative for connexin45. A clearly defined zone containing connexin45-expressing cells was, however, localized to the endocardial surface, overlapping with connexin40-expressing myocytes of the conduction system. As these results contrast with the prevailing view that connexin45 is widely distributed in working ventricular myocytes, we compared the immunolabeling pattern obtained with a commercially supplied anti-connexin45 antiserum raised against the same peptide that was used in previous studies. The commercial connexin45 antiserum gave widespread labeling throughout the ventricular myocardium, but this labeling was inhibited by a six-amino acid peptide matching part of the connexin43 sequence, indicating cross-reaction of the commercial connexin45 antiserum with connexin43 in the tissue. Further evidence for such cross-reactivity came from observations on connexin43-transfected cells, which gave positive immunolabeling with the commercial anti-connexin45 antiserum. Our demonstration of a specific association of connexin45 with connexin40-expressing myocytes in rat and mouse ventricle raises the possibility that connexin45 contributes to the modulation of electrophysiological properties in the ventricular conduction system and highlights the need for reappraisal of the distribution and role of connexin45 in other species.

Spatial relationship of the C-terminal domains of dystrophin and beta-dystroglycan in cardiac muscle support a direct molecular interaction at the plasma membrane interface

Dystrophin and beta-dystroglycan are components of a complex of at least nine proteins (the dystrophin-glycoprotein complex) that physically link the membrane cytoskeleton in skeletal and cardiac muscle, through the plasma membrane, to the extracellular matrix. Mutations in the dystrophin gene, which result in an absence or a quantitative or qualitative alteration of dystrophin, cause a subset of familial dilated cardiomyopathies as well as Duchenne and Becker muscular dystrophy. Biochemical studies on isolated skeletal muscle molecules indicate that dystrophin is bound to the glycoprotein complex via beta-dystroglycan, with the C-terminus of beta-dystroglycan binding to the cysteine-rich domain and first half of the C-terminal domain of dystrophin. Ultrastructural labeling has demonstrated a close spatial relationship between dystrophin and beta-dystroglycan in intact skeletal muscle, but no previous ultrastructural labeling studies have examined the dystrophin/beta-dystroglycan interaction in cardiac muscle. In the present study, we have applied complementary immunoconfocal microscopy and double immunogold fracture-label, a freeze-fracture cytochemical technique that allows high-resolution visualization of labeled membrane components in thin section and in platinum-carbon replicas, to investigate the spatial relationship between dystrophin and beta-dystroglycan in rat cardiac muscle. When immunogold probes of two different sizes for the two proteins were used, "doublets" representing side-by-side antibody labeling were demonstrated in en face views at the level of the plasma membrane. The results support the conclusions that dystrophin and beta-dystroglycan directly interact at the cytoplasmic face of the rat cardiac muscle plasma membrane.

Relative susceptibility of endothelium and myocardial cells to ischaemia-reperfusion injury

We have investigated the timescale, extent and sequence of endothelial, myocardial and smooth muscle cell dysfunction following ischaemia-reperfusion in the isolated rat heart. Myocardial function in the form of aortic flow was evaluated in the working heart preparation. Vasodilatation induced by endothelium-dependent agent 5-hydroxytryptamine (5-HT) and endothelium-independent substance glyceryl trinitrate (GTN) was used to assess endothelial and smooth muscle function, respectively. The percentage recovery of 5-HT response and aortic flow (endothelial vs. myocardial function) plus 5-HT response and GTN effect (endothelial function vs. smooth muscle response) after a period of ischaemia was statistically analysed by Wilcoxon's signed rank test. A possible correlation between structural and functional changes in coronary vascular endothelium after ischaemia was also explored by comparing endothelial dysfunction with morphological assessment of endothelial damage seen after ischaemia. The experiments were performed at two clinically relevant temperatures of 20 degrees C and 4 degrees C. There was no significant difference in the percentage recovery of aortic flow and 5-HT response or in 5-HT response and GTN effect after 30 min of unprotected ischaemia at 4 degrees C. The same duration of ischaemia at 20 degrees C led to significantly better recovery of GTN effect as compared with 5-HT response, but there was no difference in the recovery of aortic flow and 5-HT response. Sixty minutes of unprotected ischaemia at both temperatures caused significantly better recovery of aortic flow and GTN effect as compared with 5-HT response; 60 min of ischaemia protected by an infusion of a cardioplegic solution (protected ischaemia) at 4 degrees C had no significant effect on the recovery of the three parameters. Periods of 90, 120, 180 and 240 min of protected ischaemia at 4 degrees C, and 60, 90 and 120 min of protected ischaemia at 20 degrees C resulted in significantly better recovery of aortic flow compared with 5-HT response and of GTN effect as compared to 5-HT response. This demonstrates varying susceptibility of different cell types to ischaemic injury and highlights the strong vulnerability of endothelium to ischaemic damage as compared with myocytes and smooth muscle cells. Furthermore, there was lack of correlation between post-ischaemic endothelial dysfunction and microscopically assessed structural damage.

Gap junction localization and connexin expression in cytochemically identified endothelial cells of arterial tissue

Vascular endothelial cells interact with one another via gap junctions, but information on the precise connexin make-up of endothelial gap junctions in intact arterial tissue is limited. One factor contributing to this lack of information is that standard immunocytochemical methodologies applied to arterial sections do not readily permit unequivocal localization of connexin immunolabeling to endothelium. Here we introduce a method for multiple labeling with specific endothelial cell markers and one or more connexin-specific antibodies which overcomes this limitation. Applying this method to localize connexins 43, 40, and 37 by confocal microscopy, we show that the three connexin types have quite distinctive labeling patterns in different vessels. Whereas endothelial cells of rat aorta and coronary artery characteristically show extensive, prominent connexin40, and heterogeneous scattered connexin37, the former, unlike the latter, also has abundant connexin43. The relative lack of connexin43 in coronary artery endothelium was confirmed in both rat and human using three alternative antibodies. In the aorta, connexins43 and 40 commonly co-localize to the same junctional plaque. Even within a given type of endothelium, zonal variation in connexin expression was apparent. In rat endocardium, a zone just below the mitral valve region is marked by expression of greater quantities of connexin43 than surrounding areas. These results are consistent with the idea that differential expression of connexins may contribute to modulation of endothelial gap junction function in different segments and subzones of the arterial system.

Effect of cardioplegia infusion pressure on coronary artery endothelium and cardiac mechanical function

OBJECTIVE

Monitoring of cardioplegia infusion pressure may be important, particularly in immature hearts and in hearts without coronary artery disease. We have investigated the effects of infusion pressure on the preservation of the isolated rat heart.

METHODS

Hearts (five in each group) were subjected to a single (20 ml) infusion of St. Thomas' Hospital cardioplegic solution at pressures of 60, 120, 180 and 240 cmH2O (44-176 mmHg), followed by 30 min of hypothermic (20 degrees C) ischemia.

RESULTS

Mean recovery of cardiac output (expressed as a percentage of its preischemic value) decreased with increasing infusion pressure: 96.1 +/- 0.6%, 87.3 +/- 2.1% (P < 0.05 vs. 60 cmH2O), 79.3 +/- 2.8% (P < 0.05 vs. 120 cmH2O), 72.0 +/- 3.0% (not significant vs. 180 cmH2O), respectively. Endothelial function, as assessed by pre- and post-ischemic ability to secrete NO in response to 5-hydroxytryptamine, remained relatively normal after infusion at 60 cmH2O, but changed from vasodilation to vasoconstriction after infusion at 240 cmH2O. Electron microscopy revealed mild endothelial damage after infusion at 240 cmH2O, which was greatly exacerbated by reperfusion and was accompanied by regions of myocyte damage compatible with reperfusion of unprotected myocardium. The relationship between cardioplegia infusion pressure and infusion time was not linear and implied that infusion pressures greater than 120 cmH2O caused vascular smooth muscle constriction.

CONCLUSIONS

These results suggest that even mildly raised cardioplegia infusion pressures may be detrimental to cardiac preservation and the effects are possibly mediated through endothelial damage and pressure-induced coronary vasoconstriction.

Dystrophin is not a specific component of the cardiac costamere

Dystrophin is a key component of the subsarcolemmal skeleton of muscle cells, and lack of dystrophin is the direct cause of Duchenne muscular dystrophy. In skeletal muscle, dystrophin is reported to be localized specifically at costameres, transversely oriented riblike subsarcolemmal plaques that mechanically couple the contractile apparatus to the extracellular matrix. Costameres are characteristically rich in vinculin and are prominent in cardiac as well as skeletal muscle. To define the precise spatial relationship between dystrophin in relation to the costamere in cardiac muscle, we applied high-resolution single- and double-immunolabeling techniques, under a range of preparative conditions, with visualization of vinculin (as a costamere marker) and dystrophin by confocal microscopy and by the freeze-fracture cytochemical technique, fracture label. Immunoconfocal visualization revealed dystrophin as a continuous uniform layer at the cytoplasmic surface of the peripheral plasma membrane of the rat cardiac myocyte at both costameric and noncostameric regions. The pattern of labeling was reproducible with three different antibodies and was independent of time and antibody concentration. Platinum/carbon replicas and thin sections of fracture-label specimens permitted high-resolution visualization of the distribution of dystrophin in plane views of the freeze-fractured plasma membrane and in relation to the sarcomeric banding patterns of the underlying myofibrils. These results confirmed no preferential association of dystrophin with costameres or with any region of the sarcomeres of underlying myofibrils in rat cardiac tissue. We conclude that in contrast to skeletal muscle, dystrophin in cardiac muscle is not exclusively a component of the costamere.

Dissociated spatial patterning of gap junctions and cell adhesion junctions during postnatal differentiation of ventricular myocardium

Nonuniformity in the spatial patterning of gap junctions between heart muscle cells is now recognized as an important determinant of electromechanical function in working myocardium. Breakdown of the normal geometry of electrical intercellular connectivity in diseased myocardium correlates with reentry, arrhythmia, and conduction disturbance. The developmental mechanism(s) that determines this precise spatial order in gap junction organization in normal myocardium is at present unknown. To examine this question, we have used immunoelectron and immunoconfocal microscopy to analyze the spatial distributions of gap junctional (connexin43), desmosomal (desmoplakin), and adherens junctional (N-cadherin) components during maturation of rodent and canine left ventricular myocardium. In rats, a striking divergence in the distribution of gap junctions and cell adhesion junctions emerged within the first 20 days of postnatal life. It was found that although gap junctions initially demonstrated dispersed distributions across myocyte cell membranes, desmosomes and adherens junctions showed more rapid polarization toward cell termini (ie, nascent intercalated disks) after birth. Over subsequent postnatal development (20 to 90 postnatal days), gap junctions became progressively concentrated in these cell adhesion junction-rich zones of membrane. Quantitative analyses of this process in a series of rats aged 15 embryonic and 1, 5, 10, 20, 40, 70, and 90 postnatal days indicated that significantly higher levels (P < .01) of N-cadherin and desmoplakin than of connexin43 were immunolocalized to cell termini by as early as postnatal day 5. Although all three junctions types showed increasing polarization to myocyte termini with development, variation between junctions remained significant (P < .05) at all times points between 5 and 70 postnatal days. Only at 90 postnatal days, when the animals were nearly full grown, did the proportions of gap junction, desmosome, and adherens junction at intercalated disks become statistically similar (P > .05). Examination of myocardium from 1- and 3-month-old canines revealed that related differential changes to the spatiotemporal distribution of intercellular junctions occurred during postnatal maturation of the dog heart, suggesting that the process was not rodent specific. It is concluded that this progressive change in the organization and pattern of association between gap junctions and cell adhesion junctions is likely to be an important factor in maturation of electromechanical function within the mammalian heart.

Quantitative immunoconfocal analysis of human myometrial gap junction connexin43 in relation to steroid hormone concentrations at term labour

The aim of this study was to quantify gap junction expression in the human myometrium in relation to progesterone and oestradiol concentrations, and to establish whether oxytocin-resistant dystocia is due to an abnormality in gap junction expression. Three groups of patients were investigated: (i) before labour (at term), (ii) normal labour and (iii) oxytocin-resistant dystocia (eight patients per group). For each patient, the concentrations of oestradiol and progesterone in maternal blood and in myometrial tissue were measured, and the number and area of immunostained connexin43 gap junctions per unit volume of tissue determined by quantitative analysis of digital images obtained by confocal microscopy. No significant difference in connexin43 gap junction content was observed between the three patient groups. When all groups were pooled, there was a significant positive correlation (P < 0.05) between the quantity of immunolabelled gap junctions and the oestradiol:progesterone ratio, but there was no significant difference in this correlation between the groups. Gap junction immunolabelling was not correlated with the progesterone or oestradiol concentration in the maternal blood or the myometrium. These data suggest that in human myometrium: (i) dystocia is not due to a reduced level of immunodetectable connexin43 gap junctions, (ii) onset of labour is not associated with a sudden increase in immunodetectable gap junction protein and (iii) gap junctions can be expressed in the presence of high progesterone concentrations.

Spatial distribution of dihydropyridine receptors in the plasma membrane of guinea pig cardiac myocytes investigated by correlative confocal microscopy and label-fracture electron microscopy

Excitation-contraction coupling in cardiac muscle is thought to depend fundamentally on the spatial organization of sarcolemmal dihydropyridine receptors (L-type calcium channels) in relation to ryanodine receptors (calcium-release channels of the sarcoplasmic reticulum). In the present study, we have investigated the distribution of dihydropyridine receptors in the guinea pig myocyte plasma membrane by correlative immunoconfocal microscopy and label-fracture electron microscopy. Label-fracture, a method in freeze-fracture cytochemistry, permits immunogold localization of cell surface proteins in en face membrane views. Taken together, results from confocal microscopy and label-fracture replicas suggest that, in the peripheral plasma membrane, calcium channels are organized predominantly in the form of clusters. Confocal microscopy also suggests a similar organization in the transverse tubules. It is hypothesized that these clusters may lie adjacent to junctional sarcoplasmic reticulum, permitting the close coupling of influx of calcium through plasma membrane calcium channels to trigger release of calcium from the intracellular stores, as part of the mechanism of calcium-induced calcium release.

Upregulation of connexin43 gap junctions during early stages of human coronary atherosclerosis

Interactions between cells form the framework for understanding the pathogenesis of atherosclerosis, but little information is available on the role of direct intercellular communication via gap junctions in this process. To investigate gap junction expression in the pathogenesis of human atherosclerosis, lesions representing different stages of the disease were obtained from coronary arteries of hearts removed from patients undergoing cardiac transplantation. Twelve hearts, each providing 1 to 3 segments of artery, were used in the study. Sections were examined by confocal laser scanning microscopy after immunofluorescent labeling with a specific antibody against connexin43, the major gap-junctional protein of smooth muscle cells, to permit high-definition visualization of immunolabeled gap junctions through the depth of the specimen. Double labeling using anti-connexin43 and cell type-specific antibodies demonstrated colocalization of gap junctions with smooth muscle cells but not with macrophages, a relationship confirmed by electron microscopy. Regions of intimal thickening and early atheromatous lesions showed markedly increased expression of connexin43 gap junctions between intimal smooth muscle cells compared with the undiseased vessels. This increase in gap junctions was most marked in regions of intimal thickening, semiquantitative analysis of the confocal digital images revealing a > 10-fold increase compared with the undiseased vessel. The quantity of labeled gap junctions in early atheromatous lesions, although higher than that of the undiseased vessel, was lower than that of intimal thickenings, and this trend toward reduced levels of gap junction immunolabeling with lesion progression continued, the value observed in the most advanced atheromatous lesions being lower than that of the undiseased vessel. As the quantity of gap junctions declined, their distribution became more patchy and the sizes of individual junctions larger. The results suggest that enhanced expression of gap junctions between smooth muscle cells may play a role in maintaining the synthetic phenotype during early growth of the atherosclerotic plaque.

Validation of immunohistochemical quantification in confocal scanning laser microscopy: a comparative assessment of gap junction size with confocal and ultrastructural techniques

Confocal scanning laser microscopy (CSLM) is increasingly being used to image antibody-labeled structures visualized with a fluorescent secondary antibody. Such digital images are routinely stored on computer and are well suited to quantitative analysis. Although theoretical aspects of CSLM imaging and resolution are well defined, information is lacking on the relationship observed between measurements of fluorescent antibody-labeled structures and the size of the same structures as determined by electron microscopy (EM). In the present study we examined this relationship for the cardiac gap junction. Data on the size of immunofluorescent-labeled gap junctions were acquired by two methods of analysis from CSLM images and compared statistically with measurements of gap junction size obtained by freeze-fracture EM. The freeze-fracture data were compared before and after exclusion of small junctions, corresponding to those that theoretically would not have been detected in CSLM analysis. The data obtained by the different methods were similar but not identical, reflecting the advantages and limitations of each technique. However, the comparison did indicate that with appropriate sample preparation and orientation, accurate and rapid analysis can be achieved by CSLM, particularly when digital semi-automated techniques are employed.

The spatial distribution and relative abundance of gap-junctional connexin40 and connexin43 correlate to functional properties of components of the cardiac atrioventricular conduction system

Electrical coupling between heart muscle cells is mediated by specialised regions of sarcolemmal interaction termed gap junctions. In previous work, we have demonstrated that connexin42, a recently identified gap-junctional protein, is present in the specialised conduction tissues of the avian heart. In the present study, the spatial distribution of the mammalian homologue of this protein, connexin40, was examined using immunofluorescence, confocal scanning laser microscopy and quantitative digital image analysis in order to determine whether a parallel distribution occurs in rat. Connexin40 was detected by immunofluorescence in all main components of the atrioventricular conduction system including the atrioventricular node, atrioventricular bundle, and Purkinje fibres. Quantitation revealed that levels of connexin40 immunofluorescence increased along the axis of atrioventricular conduction, rising over 10-fold between atrioventricular node and atrioventricular bundle and a further 10-fold between atrioventricular bundle and Purkinje fibres. Connexin40 and connexin43, the principal gap-junctional protein of the mammalian heart, were co-localised within atrioventricular nodal tissues and Purkinje fibres. By applying a novel photobleach/double-labelling protocol, it was demonstrated that connexin40 and connexin43 are co-localised in precisely the same Purkinje fibre myocytes. A model, integrating data on the spatial distribution and relative abundance of connexin40 and connexin43 in the heart, proposes how myocyte-type-specific patterns of connexin isform expression account for the electrical continuity of cardiac atrioventricular conduction.

Expression of connexin43 gap junctions between cultured vascular smooth muscle cells is dependent upon phenotype

The smooth muscle cell is the predominant cell type of the arterial media. In the adult vascular system, smooth muscle cells are found primarily in the contractile phenotype, but following injury or during atherosclerotic plaque formation the secretory synthetic phenotype is expressed. Recently it has been shown that gap junction connexin43 messenger RNA levels are six times higher in cultured smooth muscle cells in the synthetic phenotype than in intact aorta. We have modulated rabbit aortic smooth muscle cells in culture between the synthetic phenotype and one resembling the contractile phenotype, and correlated gap junction expression with phenotype. A dual labelling technique with antibodies against smooth muscle myosin and a synthetic peptide constructed to match a portion of the connexin43 gap junction protein was used for these experiments. Gap junctions are numerous between synthetic phenotype cells but few are observed between contractile cells. Rat aortic smooth muscle cells were also cultured and the growth and structure of gap junctions followed in the synthetic phenotype by use of freeze-fracture electron microscopy and immunohistochemical techniques. Junctional plaques are similar in structure to those observed in cardiac muscle, their size and number increasing with time in culture. The increased numbers of gap junctions between synthetic phenotype smooth muscle cells may be important during vessel development, following injury, or in atherosclerotic plaque formation.

Detrimental effects of temperature on the efficacy of the University of Wisconsin solution when used for cardioplegia at moderate hypothermia. Comparison with the St. Thomas Hospital solution at 4 degrees C and 20 degrees C

BACKGROUND

We have previously reported the superior protective properties of the University of Wisconsin (UW) solution compared with the St. Thomas solution (ST) in the rat heart subjected to the deep hypothermia (4 degrees C), thus demonstrating its possible use in cardiac transplantation. We thought it was important to evaluate the potential of the UW solution as a cardioplegic solution under the moderately hypothermic (20 degrees C) conditions of routine intraoperative myocardial protection.

METHODS AND RESULTS

Isolated rat hearts were subjected to 60 minutes of ischemia at 4 degrees C or 30 (or 60) minutes of ischemia at 20 degrees C with UW, ST, and ST plus 100 mM K (ST + 100) solutions. Coronary flow, mechanical function, endothelial function, and ultrastructure were observed. Mean time (seconds) to infuse 10 ml of cardioplegic solution under constant pressure, a measure of coronary vascular resistance at 4 degrees C and 20 degrees C, respectively, for each solution were ST, 69.2 +/- 6.9 and 64.7 +/- 3.8; UW, 142.2 +/- 8.8 and 187.2 +/- 10.0 (p < 0.01); and ST + 100, 78.2 +/- 8.0 and 176 +/- 8.1 (p < 0.001). Mean recovery values of cardiac output (expressed as percentage of its preischemic value) after 60 minutes of ischemia at 4 degrees C were ST, 95.5 +/- 2.1%; UW, 93.0 +/- 2.4%; and ST + 100, 96.5 +/- 1.5%. After 30 minutes of ischemia at 20 degrees C, values were ST, 88.0 +/- 1.3%; UW, 72.2 +/- 3.6% (p < 0.005 versus ST); and ST + 100, 53.3 +/- 1.8% (p < 0.001 versus ST).

CONCLUSIONS

The efficacies of UW and severely hyperkalemic cardioplegic solutions are affected by the degree of hypothermia under which they are used. Under moderate hypothermia (20 degrees C), severe hyperkalemia induces a marked increase in coronary vascular resistance that is associated with impaired myocardial protection. These studies discourage the use of UW for routine intraoperative cardioplegic arrest where the degree of hypothermia cannot be readily controlled. The ST solution does not share this constraint.

Superior qualities of University of Wisconsin solution for ex vivo preservation of the pig heart

The components of the University of Wisconsin solution have the potential to enhance and extend heart preservation. We have evaluated University of Wisconsin solution by comparing it with St. Thomas' Hospital cardioplegic solution in the isolated pig heart subjected to 8 hours of ischemia at 4 degrees C (n = 6 in each). The hearts were perfused ex vivo with enriched autologous blood for the control and the postpreservation assessments. Morphologic, metabolic, and functional evaluations were performed. Left and right ventricular function as assessed by the slope values of systolic and diastolic pressure-volume relationships of isovolumically contracting isolated heart was better preserved by University of Wisconsin solution (percent reduction: left ventricular systolic, 52.4% +/- 5.5% versus 17.7% +/- 6.7% [p less than 0.001]; right ventricular systolic, 125.6% +/- 46.4% versus 65.5% +/- 31.4% [p less than 0.05]; right ventricular diastolic, 112.3% +/- 48.7% versus 40.2% +/- 31.3% [p less than 0.02] after St. Thomas' Hospital and University of Wisconsin preservation, respectively). Postischemic recovery of left ventricular rate of rise of pressure and myocardial oxygen consumption were significantly improved after University of Wisconsin preservation (percent reduction, rate of rise of pressure: St. Thomas' Hospital 39.3% +/- 8.1%; University of Wisconsin 18.1% +/- 4.6%; percent reduction, myocardial oxygen consumption St. Thomas' Hospital 55.1% +/- 6.9%, University of Wisconsin 24.8% +/- 6.7%; p less than 0.001). Microvascular functional integrity as assessed by coronary vascular resistance was well maintained throughout the postischemic period and was similar to the preischemic control value in the University of Wisconsin group. By contrast, a significant increase was found at the beginning of postpreservation reperfusion, with a progressive rise thereafter in the St. Thomas' Hospital group (p less than 0.001). Preservation of myocardial adenosine triphosphate was improved and energy charge was unchanged after 8 hours of ischemia and reperfusion in the University of Wisconsin-preserved hearts compared with the St. Thomas' Hospital-preserved hearts (p less than 0.01). Electron microscopic examination revealed substantially better preservation of the contractile apparatus after preservation with University of Wisconsin solution. Myocytes from hearts receiving University of Wisconsin solution, unlike those given St. Thomas' Hospital solution, showed relaxed myofibrils with prominent I-bands. We conclude that University of Wisconsin solution has the potential to improve the preservation of the heart and possibly prolong the ischemic period in clinical cardiac transplantation.

Altered patterns of gap junction distribution in ischemic heart disease. An immunohistochemical study of human myocardium using laser scanning confocal microscopy

Arrhythmias are a common and potentially life-threatening complication of myocardial ischemia and infarction in humans. The structural pathways for the rapid intercellular conduction of the electrical impulse that stimulates coordinated contraction in the myocardium are formed by the gap junctions situated at intercalated disks. By raising antibodies to cardiac gap-junctional protein, and using these antibodies in an immunohistochemical procedure in combination with the technique of laser scanning confocal microscopy, we have succeeded in localizing gap junctions, with a clarity not previously possible, through thick volumes of human myocardial tissue. To explore the structural basis for ischemia and infarction-related arrhythmogenesis, antibody labeling and laser scanning confocal microscopy were applied to study the organization, distribution, and other characteristics of gap junctions in the explanted hearts of patients undergoing cardiac transplantation for advanced ischemic heart disease. In areas of myocardium free from histologically detectable structural damage, there was no significant difference in the size of distribution of labeled gap junctions, or in their number per intercalated disk, between left ventricular tissue (in which functional impairment was severe) and right ventricular tissue (in which functional impairment was minimal). However, in myocytes at the border of healed infarcts--zones to which the slow conduction responsible for reentry arrhythmias has been localized--the organization of gap junctions was markedly disordered; instead of being aggregated into discrete intercalated disks, gap-junctional immunostaining was spread extensively over myocyte surfaces. Some infarct zones were bridged by continuous strands of myocytes, coupled to one another by gap junctions, thereby linking healthy myocardium on either side. At their thinnest, these bridges were in some instances no wider than a single attenuated myocyte. The conclusions are 1) a widespread, generalized derangement of gap junction organization does not appear to underlie functional impairment in the ischemic heart, 2) a disorderly arrangement typifies gap junctions in myocytes of the infarct border zone, and this may contribute to alterations in conduction that are capable of precipitating reentry arrhythmias, and 3) delicate chains of myocytes traverse some healed infarcts, apparently forming electrically coupled bridges across what would otherwise constitute blocked zones. The weakest link in this chain can be a single, degenerating myocyte; avoidance of arrhythmia may therefore depend on the continued survival of this single cell.

Formation of "vessel-like" structures by retinal capillary endothelial cells in culture

The formation of "vessel-like" structures has been previously reported in cultures of endothelial cells from both large and small vessels. In this study the formation of such tubular structures was observed in post-confluent cultures of bovine retinal microvascular endothelial cells. As the cells became postconfluent, cell dropout occurred and the remaining islands of cells were observed to be interconnected by cords. Electron microscopy demonstrated that each cord consisted of a continuous lumen surrounded by one or more endothelial cells. The mechanisms of in vitro "vessel formation" by retinal endothelial cells do not appear to relate to either those of embryonic retinal vascularisation or those associated with retinal neovascularisation and may be an unrelated phenomenon only expressed in vitro.

Long-term healing of the central cornea after photorefractive keratectomy using an excimer laser

Using an excimer laser at 193 nm, 3-mm diameter discs were ablated from the optical zone of monkey corneas at a variety of depths up to 130 micron. Tissue was examined by light and electron microscopy 4 and 5 weeks and 6 and 8 months postoperatively. With the exception of the deepest ablation, all corneas were clear immediately postoperatively. At 1 month, ablations of 40 micron remained clear, whereas all others showed some degree of haze. By 3 months, discs at 60 micron depth were clear, and there was less haze in others. Haze was progressively lost over 6 months, but in the deepest discs it could still be discerned on slit-lamp examination. Microscopic observation showed that reepithelialization had occurred within 24 to 48 hours. Over subsequent months, a normal morphology was maintained in this layer with the exception that basal cells were slightly more elevated particularly at the disc margins where the epithelium contained more cell layers. Stromal reorganization was accompanied by an initial phase of vacuolation and invasion by keratocytes, but by 6 months postoperatively almost all vacuolation had disappeared and keratocyte numbers had almost returned to normal. By 8 months, the morphology was near normal with the exception that Bowman's membrane was absent and there was still a degree of disorder in the immediate subepithelial stromal fibers. The basement membrane of epithelial cells was reestablished but slightly more undulant than in nonirradiated areas. This undulation was retained in the 8-month postoperative specimens and at this time a normal thickness of 60 nm was displayed.

Ultrastructural comparison of conventional surgical and argon fluoride excimer laser keratectomy

We used scanning electron microscopy to examine the structure of the surfaces created during keratectomy procedures carried out by conventional surgery and ablation by an excimer laser. The walls and the floor of the surgical site were rough with undulations greater than 10 micron in size, caused by broken lamellae and ruptured cells. In contrast, the surfaces produced by the excimer laser were smooth with perturbations of 1 micron or less and were sealed with a pseudomembrane. This smooth, sealed surface produced by the laser is probably responsible for the transparency of the healed cornea in contrast to the scarring produced when a conventional surgical keratotomy heals.

A comparative study of corneal incisions induced by diamond and steel knives and two ultraviolet radiations from an excimer laser

This paper reviews the potential role of excimer lasers in corneal surgery. The morphology of incisions induced by two wavelengths of excimer laser radiation, 193 nm and 248 nm, are compared with the morphology of incisions produced by diamond and steel knives. Analysis suggests that ablation induced by excimer laser results from highly localised photochemical reactions and that 193 nm is the optimal wavelength for surgery. The only significant complication of laser surgery is loss of endothelial cells when incisions are within 40 micron of Descemet's membrane.

Extensive subretinal pigment epithelial deposit in two brothers suffering from dominant retinitis pigmentosa. A histopathological study

The eyes of two brothers with retinitis pigmentosa were removed after death and examined by a variety of techniques, including conventional histology, fluorescence microscopy and both scanning and transmission electron microscopy. Their condition was considered to be of an autosomal dominant type but with some atypical clinical features. The outstanding histological feature in both pairs of eyes was a predominantly acellular deposit of amorphous material situated between the retinal pigment epithelium and Bruch's membrane. This material extended from the disc to beyond the ora serrata. In some regions of the retinae of both brothers, there was a cellular infiltrate into the deposit and this included multinucleate cells. In one brother the deposit was lined externally by a fibrovascular membrane in some few locations. All retinae were degenerate, but all showed preservation of abnormally short and sparse photoreceptor cells in both the peripheral and macular areas. There was only patchy loss of the choriocapillaris, which could have been age-dependent rather than disease-dependent, and the remaining choroidal vessels were patent in all cases. The widespread distribution of the deposit is unusual and suggests that it arises from disordered metabolism of the retinal pigment epithelium. We could not determine whether it was a primary disease process or if it arose as a secondary phenomenon.

An ultrastructural study of corneal incisions induced by an excimer laser at 193 nm

Far ultraviolet light (193 nm) produced by an excimer laser has been used to produce a variety of incisions in the corneas of anaesthetised rabbits. Tissue was lost from the site of irradiation but the nature of the underlying molecular interactions responsible for such tissue erosion remain obscure. Ultrastructural analysis of the walls of the ablated areas show damage to the adjacent structures to be confined to a zone 60 to 200 nm in width. These dimensions could either be attributed to photochemical processes in which high energy photons directly break organic molecular bond, or to thermal reactions which result in limited heat flow and damage confined to the absorption depth at 193 nm of less than 1 micron. In non-penetrating incisions that reached within 40 micron of Descemet's membrane, endothelial cells were lost beneath the line of the irradiation. This spalling of cells seemed to be generated by shock or acoustic waves.