Electrical coupling of individual electrocatalytic oscillators

The catalytic electro-oxidation of some small organic molecules is known to display kinetic instabilities, which reflect on potential and/or current oscillations. Under oscillatory conditions, those systems can be considered electrocatalytic oscillators and, therefore, can be described by their amplitude, frequency, and waveform. Just like mechanical oscillators, the electrocatalytic ones can be coupled and their dynamics can be changed by setting different coupling parameters. In the present work, we study the unidirectional coupling of electrocatalytic oscillators, namely, those comprehending the catalytic electro-oxidation of methanol and formic acid on polycrystalline platinum in acidic media under potentiostatic control. Herein, we explore two different scenarios (the coupling of compositionally identical and non-identical oscillators) and investigate the effects of the master's identity and of the coupling constant on the slave's dynamics. For the master (methanol)-slave (methanol) coupling, the oscillators exhibited phase lag synchronization and complete phase synchronization. On the other hand, for the master (formic acid)-slave (methanol) coupling, the oscillators exhibited complete phase synchronization with phase-locking with a 2:3 ratio, complete phase synchronization with phase-locking with a 1:2 ratio, phase lag synchronization, and complete phase synchronization. The obtained results suggest that both the master's identity and the coupling constant (sign and magnitude) are parameters that play an important role on the coupled systems, in such a way that even for completely different systems, synchronization could emerge by setting a suitable coupling constant. To the best of our knowledge, this is the first report concerning the electrical coupling of hidden N-shaped-negative differential resistance type systems.

Voltammetric investigation on iron-(nickel-)sulfur surface under conditions for the emergence of life

Iron (II) sulfide minerals have gained attention in the last decades due to their relevance in hypotheses for the emergence of life on the early Earth around 4 billion years ago. In the submarine vent theory, it has been proposed that those minerals, especially mackinawite, had a key role in prebiotic processes. Those are estimated to be present in a natural electrochemical setting, analogous to a chemiosmotic one, formed in the interface between the early ocean and the interior of the alkaline hydrothermal systems, the early vent-ocean interface. To evaluate this and other hypotheses, voltammetric studies were performed to better understand the electrochemical behavior of minerals under conditions analogous to the vent-ocean interface. The preliminary results presented here indicate that, in the potential range estimated to exist in that interface, mackinawite can transition to other mineral phases and may posibly coexist with other minerals, resulting from its oxidation. This can create a local chemical diversity. In addition, it has been tested a protocol for Ni incorporation in mackinawite structure, resulting in a surface that showed an interesting behavior in the presence of CO2, although definitive experiments showed necessary for a deeper comprehension of that behavior. Overall, the results are consistent with previous results on electrocatalytical properties of Fe-Ni-S materials for CO2 reduction, and also could lead to the emergence of a protometabolism on early Earth.

Probing the surface fine structure through electrochemical oscillations

In the course of (electro)catalytic reactions, reversible and irreversible changes, namely the formation of adsorbed poisons, catalyst degradation, surface roughening, etc., take place at distinct time-scales. Reading the transformations on the catalyst surface from the measurement of the reaction rates is greatly desirable but generally not feasible. Herein, we study the effect of random surface defects on Pt(100) electrodes toward the electro-oxidation of methanol in acidic media. The surface defects are gently generated in situ and their relative magnitudes are reproducibly controlled. The system was characterized under conventional conditions and investigated under an oscillatory regime. Oscillatory patterns were selected according to the presence of surface defects, and a continuous transition from large amplitude/low frequency oscillations (type L) on smooth surfaces to small amplitude/high frequency oscillations (type S) on disordered surfaces was observed. Importantly, self-organized potential oscillations were found to be much more sensitive to the surface structure than conventional electrochemical signatures or even other in situ characterization methods. As a consequence, we proved the possibility of following the surface fine structure in situ and in a non-invasive manner by monitoring the temporal evolution of oscillatory patterns. From a mechanistic point of view, we describe the role played by surface defects and of the adsorbed and partially oxidized, dissolved species on the oscillations of type S and L.

Pericytes. Morphofunction, interactions and pathology in a quiescent and activated mesenchymal cell niche

We review the morphofunctional characteristics of pericytes and report our observations. After a brief historical background, we consider the following aspects of pericytes: A) Origin in embryonic vasculogenesis (mesenchymal stem cells, neurocrest and other possible sources) and in embryonic and postnatal life angiogenesis (pre-existing pericytes, fibroblast/ myofibroblasts and circulating progenitor cells). B) Location in pericytic microvasculature and in the other blood vessels (including transitional cell forms and absence in lymphatic vessels), incidence (differences depending on species, topographical location, and type and stage of vessels) and distribution (specific polarities) in blood vessels. C) Morphology (cell body, and longitudinal and circumferential cytoplasmic processes), structure (nucleus, cytoplasmic organelles and distribution of microtubules, intermediate filaments and microfilaments) and surface (caveolae system). D) Basement membrane disposition, formation, components and functions. E) Contacts with endothelial cells (ECs) (peg and socket arrangements, adherent junctions and gap junctions) and with basal membrane (adhesion plaques). F) Molecular expression (pericyte marker identification). G) Functions, such as vessel stabilization, regulation of vascular tone and maintenance of local and tissue homeostasis (contractile capacity and vessel permeability regulation), matrix protein synthesis, macrophage-like properties, immunological defense, intervention in coagulation, participation in mechanisms that regulate the quiescent and angiogenic stages of blood vessels (including the behaviour of pericytes during sprouting angiogenesis and intussuceptive vascular growth, as well as pericyte interactions with endothelium and other cells, and with extracellular matrix) and plasticity, as progenitor cells with great mesenchymal potential, originating other pericytes, fibroblast/myofibroblasts, preadipocytes, chondroblasts, osteoblasts, odontoblasts, vascular smooth muscle and myointimal cells. This mesenchymal capacity is seen in a broad section on the perivascular mesenchymal cell niche hypothesis and in the concept of pericyte and EC "marriage and divorce". H) Peculiar pericyte types, such as hepatic stellate cells (Ito cells), bone marrow reticular cells and mesangial cells. I) Involvement in pathological processes, such as repair through granulation tissue, pericyte-derived tumors, tumor angiogenesis and tumoral cell metastasis, diabetic microangiopathy, fibrosis, atherosclerosis and calcific vasculopathy, lymphedema distichiasis, chronic venous insufficiency, pulmonary hypertension, Alzheimer disease and multiple sclerosis. J) Clinical and therapeutic implications (de-stabilization of vessels or formation of a stable vasculature).

Histogenesis and morphofunctional characteristics of chromaffin cells

This article reviews the current status of research about the histogenesis and morphofunctional characteristics of chromaffin cells in the adrenal medulla. First, this study reports the selective migration, transcription and activation factors, and the morphological events of the chromaffin cell precursors during adrenal medulla development. Subsequently, the morphofunctional characteristics of adrenergic and non-adrenergic cells are considered, with particular reference to the characteristics of chromaffin granules and their biological steps, including their formation, traffic (storage, targeting and docking), exocytosis in the strict sense and recapture. Moreover, the relationship of chromaffin cells with other tissue components of the adrenal medulla is also revised, comprising the ganglion cells, sustentacular cells, nerves and connective-vascular tissue.

Cell contribution of vasa-vasorum to early arterial intimal thickening formation

In occluded femoral artery segments, intimal thickening occurred and abundant neovascularization from the surrounding microcirculation developed. Under these conditions, the contribution of vasa-vasorum as a source of supplementary population of cells during the early intimal thickening formation was studied. Using a technique that specifically labels venules, predominantly postcapillary venules, a marker-Monastral Blue B-was used as a tracer to follow the pericyte, endothelial cell and monocyte/macrophage lineages. In the first two days of the experiment, the marker was restricted to the wall of the periarterial microcirculation, being incorporated by endothelial cells, pericytes and some monocytes/macrophages crossing the venule walls. Later, the marker continues to be observed in some of the following cells: endothelial cells and pericytes of the newly-formed vessels, fibroblast-like cells, transitional cells between pericytes and fibroblast-like cells, macrophages migrating into the interstitium, myointimal cells and neoendothelial cells of the arterial lumen. These findings provide evidence that, during arterial intimal thickening formation in occluded arterial segments, the periarterial microvascularization contributes, in addition to recruited macrophages, newly-formed endothelial cells and a supplementary population of fibroblast-like cells and myointimal cells.

Adult stem and transit-amplifying cell location

Adult stem cells (ASC)--able to self renew and to intervene in maintaining the structural and functional integrity of their original tissue--can express greater plasticity than traditionally attributed to them, adopting functional phenotypes and expression profiles of cells from other tissues. Therefore, they could be useful to regenerative medicine and tissue engineering. Transit-amplifying cells (TAC) are committed progenitors among the ASC and their terminally differentiated daughter cells. The ASC reside in a specialized physical location named niche, which constitutes a three-dimensional microenviroment where ASC and TAC are protected and controlled in their self-renewing capacity and differentiation. The niche can be located near or far from the recruitment point, requiring a short or long-distance cellular migration, respectively. This paper briefly reviews the current status of research about ASC plasticity, transdifferentiation, fusion and functional adaptation mechanisms. Subsequently, ASC and TAC occurrence, characteristics and location have been considered in the skin, cornea, respiratory tract, teeth, gastrointestinal tract, liver, pancreas, salivary glands, kidney, breast, prostate, endometrium, mesenchyma, bone marrow, skeletal and cardiac muscle, nervous system and pituitary gland. Moreover, the role of cancer ASC has also been revised.

Pattern formation in stiff oscillatory media with nonlocal coupling: a numerical study of the hydrogen oxidation reaction on Pt electrodes in the presence of poisons

The impact of the strength of negative (desynchronizing) global coupling (NGC) on the spatiotemporal dynamics of an electrochemical relaxation oscillator is studied numerically with a prototypical model, the electro-oxidation of hydrogen in the presence of poisons. The results are compared with recent experiments. The NGC has a destabilizing effect on the homogeneous oscillations. Both, in theory and in experiments, the basic patterns found with increasing global coupling strength are modulated oscillations, target patterns (including an asymmetric variant), and modulated pulses, the average spatial inhomogeneity during an oscillation increasing with the intensity of the NGC. It is suggested that this scenario is typical for strong relaxation oscillations, and a comparison with an electrochemical oscillator exhibiting harmonic oscillations points to the fact that the critical coupling strength, upon which the complete synchronization is destroyed, is larger for relaxation oscillations than for harmonic oscillations. In addition, the numerical simulations predicted two- and three-phase cluster patterns at high coupling strength. Also in experiments cluster patterns were observed, however only in parameter regions of the local dynamics which were different from the one investigated in this study.

Asymmetric target patterns in one-dimensional oscillatory media with genuine nonlocal coupling

We report the observation of a self-organized asymmetric wave source in a one-dimensional (1D) electrochemical system, namely, the hydrogen oxidation reaction on Pt in the presence of poisons. Numerical simulations reveal that the nonlocal migration coupling is crucial for the endogenous persistence of the perturbation that causes the asymmetry. Experiments and simulations agree perfectly for the regular and irregular variant of these asymmetric waves, manifesting the existence of nonlocal coupling induced patterns also in physical systems.

Spatial bifurcations of fixed points and limit cycles during the electrochemical oxidation of H2 on Pt ring-electrodes

Pattern formation during the oscillatory oxidation of H2 on Pt ring-electrodes in the presence of electrosorbing ions was studied under potentiostatic control for three different positions of the reference electrode (RE). The position of the RE crucially affects the degree of the global feedback which is imposed by the potentiostatic operation mode, and the three configurations selected corresponded to zero, maximum and intermediate global coupling. In the absence of global coupling, 'communication' among different positions occurs exclusively through migration coupling (the electrochemical counterpart to diffusion in reaction-diffusion systems). In this case, spatially inhomogeneous oscillations that were attributed to a spatial bifurcation of the homogeneous limit cycle were observed throughout. This implies that the system is Benjamin-Feir unstable. For the strongest global coupling adjustable, travelling pulses were found that emerged in a wave bifurcation with n = 1 from the homogeneous steady state. The pulses exhibited modulations in velocity and width that most likely resulted from the interaction between inhomogeneities of the catalytic surface and the nonlinear reaction dynamics. In the case of an intermediate global coupling strength, a diversity of spatio-temporal motions was observed. The dynamics ranged from pulses over target patterns and so-called asymmetric target patterns to mixed states where two or three of these states alternate. For some parameters these mixed states were in addition separated by bursts of the system to a nearly homogeneous unreactive state.

Arterial wall neovascularization induced by glycerol

An intense and significant neovascularization, with numerous capillaries growing into the media layer of the rat femoral artery, was demonstrated when glycerol was administered into the interstitium between the femoral vein and the femoral artery. The maximum microvascularization was observed at days 7 and 9 after glycerol administration. Afterwards, involution of the majority of the newly-formed microvessels in the arterial wall occurred. Other substances containing glycerol in their molecules, such as triacetyl-glycerol and tributyril-glycerol, failed to produce significant neovascularization in the media layer of the femoral artery. Neovascularization of the arterial wall was preceded by a considerable decrease in the number of the smooth muscle cells, which experienced apoptosis and necrobiosis, disappearing in extense areas of the arterial segment affected by glycerol. Coinciding with neovascularization and microvascular involution, repopulation of the media layer by smooth muscle cells was observed.

Participation of angiogenesis from rat femoral veins in the neovascularization of adjacent occluded arteries

The neovascularization of the arterial wall in human and experimental pathology has been demonstrated. The occlusion of the of the rat femoral artery is a suitable model for the study of these angiogenesis processes. Newly formed capillaries growing into the arterial wall have been described in this model. The origin of these ingrowing capillaries has been attribute to the preformed surrounding venules and capillaries. The contribution of the adjacent femoral vein with a supplementary population of vascular sprouts could also be possible. To test this hypothesis in half of the occluded arteries, the adventitia was removed from the side facing the femoral vein. Between 1 and 3 days after surgery several alterations were found both in the endothelial cells and the smooth muscle cells of the tunica media. Between 3 and 6 days, solid or canalized endothelial sprouts were observed arising from the femoral vein. By days 4 and 6, newly formed capillaries grew into the adventitia and tunica media of the femoral artery. Some of them, penetrated the internal elastic lamina. This microvascular penetration from the femoral vein was more prominent in the area of the ostium of the collateral and when the adventitia was removed. Some ingrowing capillaries were in continuity with the endothelial cells of the arterial neointima. At days 7 and 8, regressing capillaries were observed in the neomicrovasculature network between artery and vein, with a selective loss of the smaller vessels. From day 9 onwards, fewer and larger vascular channels were present between the femoral vein and the femoral artery. An arterial neolumen contained what appeared to be circulating "fresh" blood. Quantitatively, the venous neocapillary density increased from days 4 to 6 and then declined significantly by day 8. The arterial neocapillary density increased form days 4 to 8 and declined significantly by day 12. Moreover, both densities were significantly greater when the arterial adventitia was removed. The perfusion with barium solution showed the presence of the contrast material in the newly formed vessels, the lumen of the femoral vein, and the neolumen of the occluded arterial segment. The present findings indicate that putative angiogenic molecules released form the occluded arterial segment may reach the adjacent wall of the vein inducing neovascularization from it. The vein vascular sprouts are connected to the ingrowing capillaries in the occluded arterial wall and to the neocapillaries form the preexisting pericytic microvasculature. When the arterial adventitia were removed up to 2 times greater vein neocapillary's density was observed suggesting an easily access of the putative angiogenic factors to the vein.

Perineurial cell tumor (perineurioma) with granular cells

A form of benign cutaneous tumor with perineurioma findings and with the presence of associated granular cells is described. The two cases studied consisted of whorls made up of a high number of circumferentially arranged flattened cells, with perineurial characteristics, including bipolar cell processes, pinocytotic vesicles, a basal lamina, a positive immunoreactivity for EMA, and absence of immunostaining for S-100 protein. The granular cells, enclosed within the whorls, contained densely packed vesicles, particles with an apparently solid core, as well as membrane-limited vacuoles with disintegrating cellular organelles and electron-dense amorphous material. While failing to demonstrate any immunoreactivity for EMA, the granular cells showed positivity for S-100 protein, which supports their Schwann-cell origin. Due to its morphological and immunohistochemical characteristics, this peculiar form of tumor can be considered as a perineurioma with perineurial cell whorls and granular cell changes occurring in associated Schwann cells at the center of the whorls.

Induction of neovascularization in vivo by glycerol

Glycerol, injected into a site between the femoral vessels of the rat, induced neovascularization, both from the preexisting microcirculation and from the side of the femoral vein facing the artery-vein interstitium where the glycerol was administered. The use of glycerol together with a known angiogenic substance (PGE2) did not modify the neocapillary density (NCD) obtained with glycerol alone. In contrast, the lower level of NCD achieved with an acylglycerol (triacetylglycerol) was increased when the latter was associated with PGE2. Values reached were similar to, but never higher than, those for glycerol alone, or combined with PGE2. The results suggest that glycerol and some substances containing glycerol, amongst which 1-butyrylglycerol has been previously considered, may stimulate angiogenesis by a direct or indirect mechanism of action.

Contribution of the proximal and distal nerve stumps to peripheral nerve regeneration in silicone chambers

The specific contribution of the proximal and distal nerve stumps across an 8 mm gap within silicone chamber regeneration models was studied. For this, proximal and distal (Group A), distal and distal (Group B) and proximal and proximal (Group C) nerve stumps were placed in opposite ends of silicone chambers. In all the groups, a tissue cable forms between the nerve stumps, demonstrating that, without distinction, proximal or distal stumps can stimulate the growth of other proximal or distal stumps. Furthermore, in Group B, the newly formed pseudo-nerve, in the absence of regenerating axons, contains a number of Schwann cells significantly similar to Group A, which confirms that proliferation and migration of Schwann cells do not require axonal presence or contact. Likewise, the findings demonstrate that, with the exception of the axons, the distal stump contributes to the peripheral nerve regeneration in the same way as the proximal stump. Finally, when proximal stumps are placed in both the opposite ends of the silicone chamber, Schwann cells and regenerating axons grow into the chamber gap from both inserts, and myelination also proceeds from both ends to the centre of the chambers.

[Chagas disease in northern Chile. Serological prevalence in pregnant women of the city of Antofagasta, 1991-1993]

Antofagasta, the big city-port in North Chile is a triatomines free locality. Chagas infection was serologically diagnosed in 44 out of 2063 (2.1%) pregnant women from Antofagasta, studied by means of an indirect immunoflourescence test (IIFT), during 1991-1993. Out of the 44 seropositive mothers, 31 and 10 were born in the II (moderate endemic area) and IV Región (hiperendemic area), respectively. The usefulness of a screening programme for congenital Chagas' disease at primary health care in Chile is discussed.

Angiogenesis: an update

Angiogenesis is the neovascularization or formation of new blood vessels from the established microcirculation. It is particularly important and indispensable in a large number of normal and pathological processes during pre- and post-natal life, including neoplasia, inflammation, wound repair and collaterization in response to ischemic stimuli. The current interest in the role of neovascularization in the transition from hyperplasia to neoplasia, as well as in the tumour growth and metastasis, has brought about a large number of studies on angiogenesis. The complex processes of neovascularization, quiescent in the adult organism, may occur rapidly in several circumstances, with the implication of the following events: a) endothelial cell (EC) and pericyte activation; b) basal lamina degradation; c) migration and proliferation of EC and pericytes; d) formation of a new capillary vessel lumen; e) appearance of pericytes around the new capillaries; f) development of a new basal lamina; g) capillary loop formation; h) persistence or involution, and differentiation of the new vessels; and i) capillary network formation and, eventually, organization into larger microvessels. The use of numerous "in vivo" and "in vitro" systems has facilitated the assessment of angiogenesis control, in which angiogenic (fibroblast growth factors, vascular endothelial growth factor, platelet endothelial growth factor, E series prostaglandin, angiogenin, monobutyrin) and antiangiogenic (cartilage-derived angiogenic inhibitor, thrombospondin, protamine, platelet factor 4, interferon, angiostatic antibiotics, steroids) substances intervene. Heparin and heparin sulphate also play a key role in these mechanisms. A greater knowledge of angiogenesis control may lead to the development of a potential therapy in angiogenesis-related processes.

Study of Bacillus sp. culture conditions to promote production of unhairing proteases

The substitution of chemical depilatory agents in the leather industry by proteolytic enzymes produced by Bacillus species has an important economical and environmental impact. In previous assays, a Bacillus sp. showing a promising depilatory activity was isolated. In this paper, a culture medium that stimulated the synthesis and segregation of depilatory proteases, was selected. The influence of pH, oxygen supply rate (KLaC*), and inoculum age was evaluated on cell growth and protease production. Assays were carried out in lab bioreactors (1.2-1.4 l) at 37 degrees C. Five different media that differed in carbon and nitrogen sources were tested. pH ranged from 4.0 to 8.5. KLaC* varied between 40 and 470 mmol/lh. The best medium culture for protease production contained: nutrient broth (Britania) 8 g/l, yeast extract (Britania) 3 g/l, and mineral salts. Protease production was more effective at pH of 6.7, KLaC* of 360 mmol/lh, and inoculum age of 12 hours. These experimental conditions led to the following results: maximum proteolytic activity 2700 U/ml, overall volumetric protease productivity 300 u/ml-h, average specific growth rate 0.62 h-1, and average specific protease production rate 2.50 x 10(5) U/gh.

Intense vascular sprouting from rat femoral vein induced by prostaglandins E1 and E2

The formation of new capillaries from the rat femoral vein was specifically explored to assess whether venous vessels of this caliber may participate in the process of angiogenesis. Prostaglandins of the E series (PGE1 and PGE2) were administered into the soft connective tissue surrounding the rat femoral vessels as angiogenic inducers. In these conditions, between 2 and 7 days, a great number of new capillaries were observed in the media of the femoral vein, arising from the endothelial cells (EC) in the intima. The events of the capillary growth from the femoral vein included EC activation, local degradation of the basal membrane followed by migration and proliferation of EC, solid sprout formation with posterior canalization, development of a new basal membrane, and appearance of pericytes around the new capillary. Although numerous vascular buds were also observed arising from the small venules and capillaries in the periadventitial tissues, they were separated at first from those in the media of the femoral vein by the venous adventitia. Later, connections were observed between both newly formed microcirculations. The present study shows the capacity of PGE1 and PGE2 in the extravascular position of inducing capillary sprouting from veins. Furthermore, the observations provide greater evidence that vessels with characteristics similar to those of the rat femoral vein may contribute to angiogenesis, on occasion with an intense neovascularization. This fact may be of interest for the establishment of a functional circulation after angiogenesis by anastomoses of the new capillaries with those arising from pre-existing vessels of greater caliber than the venules.

Behavior of postcapillary venule pericytes during postnatal angiogenesis

Autogeneic bone marrow was implanted into an artificially created cavity in a segment of rat sciatic nerve, after removal of nerve fascicles, without damaging the epineurium or surrounding microcirculation. Under these conditions, the bone marrow induces capillary growth and forms granulation tissue from surrounding tissues, the behavior of pericytes being studied in the preformed (preexisting) postcapillary venules of the latter. Beginning 20 h after bone marrow implantation, the pericytes of the preexisting postcapillary venules hypertrophy, with shortening of their processes, prominent nucleoli, dispersal of ribosomes into their free form, fragmentation of basal lamina, and increased DNA synthesis. The number of contact surfaces between pericytes and endothelium is noticeably lower than in controls. Many pericytes are in mitosis. Cells with a shape transitional between pericytes and interstitial fibroblast-like cells appear. In some cases, Monastral Blue (MB) was used as a marker of the cells in preexisting venule walls of the graft bed. In the earlier stages of the experiment, the MB labelling is restricted to the cytoplasm of pericytes and endothelial cells of postcapillary venules, and to the macrophages that occur in the space between pericytes and endothelium. Furthermore, the marker continues to be observed, at a later stage, in some of the following cells: pericytes and endothelial cells of the newly formed vessels, macrophages migrating into the interstitium, transitional cells between pericytes and fibroblasts, and typical fibroblasts of the granulation tissue. The present study provides greater evidence that preformed microvasculature pericytes are substantially activated during postnatal angiogenesis and granulation tissue formation, suggesting that they may contribute to the origin of new pericytes and fibroblasts.

Effect of aeration rate on the alcoholic fermentation of whey by Kluyveromyces fragilis

In this paper, the influence of aeration rate on the alcoholic batch fermentation of whey by Kluyveromyces fragilis NRRL Y-2415 was investigated. Assays in 1.5-L fermentor using concentrated whey permeate containing 100 g/L of lactose were carried out at different oxygen supply rate (KLaC*) from 0 to 82 mmol/Lh. Optimum response was obtained at 14 mmol/Lh: ethanol production rate reached was 3.4 g/Lh yielding 0.46 g of product per gram of initial lactose. An increase of KLaC* from 0 to 14 mmol/Lh improved the ethanol production: maximum specific ethanol production rate (qpm) increased 3.3 times from 0.3 to 1.0 g/gh. For higher aeration levels, ethanol production diminished and biomass formation was stimulated. The declination of qpm and the increase of microns at higher aeration level lead to conclude the importance of a controlled oxygen supply in order to obtain the required balance between yeast biosynthetic needs and ethanol production.

Pericytes as a supplementary source of osteoblasts in periosteal osteogenesis

In the adult rat femur, lifting a periosteum strip with microscopic bone flakes on its deep surface, if performed without damaging the surrounding microcirculation, rapidly leads to new bone formation and angiogenesis. Using vascular labeling, the pericytes and endothelial cells (ECs) were labeled with monastral blue (MB) in the preformed, preexisting postcapillary venules of the periosteal microcirculation. MB was detectable by light and electron microscopy and it persisted in some of the daughter cells. Between one and 21 hours, the MB labeling was restricted to the pericytes and ECs of postcapillary venules. Immediately afterward, both pericytes and ECs of these vessels were activated and continued to show MB. The phenomenon of pericyte activation includes enlargement, disruption of their basal lamina, separation from the walls of the preformed vessels, and the presence of mitotic figures. At this stage, activated pericytes with MB in their cytoplasm, fibroblast-like cells, and transitional cell forms between them were seen in interstitial areas. After 27 hours, vascular buds appeared and MB was detected in some ECs and pericytes. Between three and six days, when bone-tissue development was observed, some osteoblasts were MB labeled. Previous findings support the hypothesis that when the periosteum is activated, the process of bone formation from cells already present in the periosteum is augmented by proliferation and differentiation of pericytes, which contribute a supplementary population of osteoprogenitor cells.

Microvascular pericytes: a review of their morphological and functional characteristics

A hundred years after the first description, many aspects of pericytes remain to be examined. Mesenchymal in origin, pericytes form an incomplete envelopment around the endothelial cells and within the microvascular basement membrane of capillaries and postcapillary venules. Morphologically, they appear as long, slender, polymorphic cells, showing an elongated cell body, from which arise longitudinal and circumferential branches. Cell bodies and cytoplasmic processes of pericytes, as well as the endothelial cells, are enveloped by the same basal lamina, except for where they make direct contacts with each other. The pericyte/endothelial cell contacts are peg and socket, adhesion plaques and gap junctions, making up structural mechanisms for force transmission and a possible receptor system for cells, in which the pericyte and endothelial cells respond to secondary signals generated in the other cells. Electron microscopic studies have revealed an elaborate network of cytoplasmic filaments. Pericyte intermediate filament proteins show species and tissue differences, expressing vimentin or vimentin and desmin. The pericytes also express protein typical of contractile cells, i.e. smooth muscle-specific isoforms of actin and myosin, cyclic GMP-protein kinase and tropomyosin. A gradual transition is observed between pericytes and smooth muscle cells in both terminal arterioles and venules. Several general functions for the pericytes have been postulated: contractability; permeability regulator; integrity maintainer; endothelial cell growth modulator; and cell progenitor with considerable mesenchymal potential.

Inducible perivascular cells contribute to the neochondrogenesis in grafted perichondrium

Autogeneic perichondrium was implanted above the cremaster muscle of the rat, and the new formation of two types of cartilage (types I and and II) was confirmed. Also, granulation tissue was observed before the type II cartilage formation. Under these conditions, the contribution to the neocartilage of graft bed derived cells, mainly of the venule pericytes, was studied. To follow the pericyte lineage, we used a marker--Monastral Blue B--the administration of which was based on the principle of vascular labeling. While the perichondrium was kept free, before its implantation, the preformed (preexisting) venules in the cremaster muscle were exclusively labeled with Monastral Blue B, which was incorporated into the cytoplasm of pericytes and endothelial cells. After perichondrium implantation, the following sequence in tracer distribution was demonstrated. During the earlier stages, labeling was restricted to the pericytes and endothelial cells of venules in the graft bed. Later the tracer was observed in some endothelial cells and pericytes of the growing vessels and in fibroblast-like cells of the granulation tissue. Finally, some type II neochondrocytes appeared labeled. Tracer was not found in type I neochondrocytes. The presence of label in type II neochondrocytes demonstrates that they arise from progenitor cells present in the graft bed, principally from small venule pericytes.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of the pericytes of the adventitial microcirculation in the arterial intimal thickening

Segments of rat femoral arteries, with one collateral each, occluded between ligatures and dissected from surrounding tissue, developed intimal thickening, with or without ligation of their collaterals. Numerous newly-formed capillaries from the surrounding arterial microcirculation growing into the adventitia, tunica media and intimal thickening were demonstrated by means of serial longitudinal sections, predominantly in the ostium of the collateral. When the ligatures were applied without damaging the microcirculation surrounding the artery and the normal continuity of the adventitial vessels was unchanged, earlier presence of intimal thickening was observed. When the fibrous layers of the adventitia were removed at the moment of the arterial ligation, the continuity between newly-formed vessels of the neoadventitia and those growing into the media and neointima was much more evident. It was then noted that the pericytes constituted a major component of the intimal thickening. The introduction of contrast material in microcirculation confirmed the connections between newly-formed adventitial and intimal vessels. At the beginning of the experiment, autoradiographic studies showed an increased DNA synthesis in the cells of preformed postcapillary venules and capillaries of surrounding arterial microcirculation and later in those of the newly-formed vessels growing into the arterial wall. These results indicate that newly-formed capillaries derived from surrounding arterial microcirculation penetrate the wall of the occluded arterial segments and contribute to the intimal thickening formation. It is likely that the pericytes and endothelial cells (EC) of these ingrowing vessels are sources of myointimal cells at the intimal thickening and of endothelium at the luminal surface, respectively.