LPAR2 receptor activation attenuates radiation-induced disruption of apical junctional complexes and mucosal barrier dysfunction in mouse colon.

The tight junction (TJ) and barrier function of colonic epithelium is highly sensitive to ionizing radiation. We evaluated the effect of lysophosphatidic acid (LPA) and its analog, Radioprotein-1, on γ-radiation-induced colonic epithelial barrier dysfunction using Caco-2 and m-ICC12 cell monolayers in vitro and mice in vivo. Mice were subjected to either total body irradiation (TBI) or partial body irradiation (PBI-BM5). Intestinal barrier function was assessed by analyzing immunofluorescence localization of TJ proteins, mucosal inulin permeability, and plasma lipopolysaccharide (LPS) levels. Oxidative stress was analyzed by measuring protein thiol oxidation and antioxidant mRNA. In Caco-2 and m-ICC12 cell monolayers, LPA attenuated radiation-induced redistribution of TJ proteins, which was blocked by a Rho-kinase inhibitor. In mice, TBI and PBI-BM5 disrupted colonic epithelial tight junction and adherens junction, increased mucosal permeability, and elevated plasma LPS; TJ disruption by TBI was more severe in Lpar2-/- mice compared to wild-type mice. RP1, administered before or after irradiation, alleviated TBI and PBI-BM5-induced TJ disruption, barrier dysfunction, and endotoxemia accompanied by protein thiol oxidation and downregulation of antioxidant gene expression, cofilin activation, and remodeling of the actin cytoskeleton. These data demonstrate that LPAR2 receptor activation prevents and mitigates γ-irradiation-induced colonic mucosal barrier dysfunction and endotoxemia.

Modulation of radiation-induced oral mucositis (mouse) by dermatan sulfate: effects on differentiation processes.

PURPOSE: During head and neck cancer radiotherapy, oral mucositis is the most frequent early side effect. Systemic dermatan sulfate (DS) administration has been shown to significantly decrease oral mucosal radiation reactions during daily fractionated irradiation (IR) in an established mouse model. The aim of this study was to investigate the mechanism of the oral epithelial differentiation process, during IR alone and in combination with DS treatment in the same mouse model. METHODS: Fractionated IR 5â€¯× 3 Gy/week was given to the snouts of mice over two weeks, either alone (IR) or in combination with daily DS treatment of 4 mg/kg (IR + DS). Groups of mice (n = 3) were sacrificed every second day over the course of 14 days in both experimental arms. Their tongue was excised and subjected to immunohistochemical processing. RESULTS: In the p16 analysis as a proliferation marker, the difference between IR alone and IR + DS in the germinal (proliferation) layer was not significant, not stimulating the proliferation process. For the p21 analysis as a differentiation marker on the functional (differentiation) layer, the difference between IR alone and IR + DS arms was significant, indicating that DS inhibited the differentiation process. In the cytokeratin (CK) analysis as the indicator of cellular skeletal integrity, the percentage of antibody-positive cells was above the normal level in both experimental arms and significantly superior in the IR + DS arm. CONCLUSION: The mucosal protective activity of DS, instead of stimulating proliferation, is based on prevention of cell loss by a combination of effects leading to the inhibition of cellular differentiation and an increase in the expression of epithelial mechanical strength between intercellular mechanical junctions.

Ionizing Radiation Enhances Paracellular Permeability Through Alteration of Intercellular Junctions in Cultured Human Lymphatic Endothelial Cells.

BACKGROUND: A problematic complication after radiation therapy is lymphedema. Development of lymphedema is associated with an increase in lymphatic paracellular permeability. The current study investigated the effects of radiation on intercellular junctions and paracellular permeability in cultured human dermal lymphatic endothelial cells (HDLECs). METHODS AND RESULTS: Double immunofluorescence staining with vascular endothelial (VE)-cadherin and actin immediately after X-ray irradiation (5 or 20 Gy) was performed. Morphological changes induced by irradiation were assessed. Cell viability and paracellular permeability after irradiation were also evaluated. Broad junctions in which VE-cadherin was accumulated at cell-cell contacts and almost colocalized with actin were significantly decreased in a dose-dependent manner in confluent and sparse irradiated HDLECs. Irradiation shortened the width of VE-cadherin-positive areas at the cell-cell contacts. Actin filaments did not colocalize with VE-cadherin after 20 Gy irradiation. Although cell viability was not affected by irradiation, paracellular permeability significantly increased in a dose-dependent manner. CONCLUSIONS: A dose of 5 or 20 Gy irradiation in HDLECs does not affect cell viability, but changes VE-cadherin mediated intercellular junctions and actin structure, resulting in an increase of paracellular permeability. Further investigations on the regulatory proteins involved in radiation-induced changes, which were observed in the current study, may contribute to development of lymphedema therapy.

Post-Irradiated Human Submandibular Glands Display High Collagen Deposition, Disorganized Cell Junctions, and an Increased Number of Adipocytes.

Salivary glands are vital for maintaining oral health. Head and neck radiation therapy is one of the most common causes of salivary gland hypofunction. Little is known about the structural changes that occur in salivary glands after radiation therapy. The aim of this study is to understand the structural changes that occur in post-irradiated human (submandibular gland [SMG]) as compared with untreated ones. We determined changes in epithelial polarity, presence of collagen deposition, and alteration in adipose tissue. We used formalin-fixed paraffin-embedded human SMG from two female subjects exposed to head and neck irradiation. We utilized hematoxylin and eosin staining and Masson's Trichrome staining. The immunostained tissue sections were examined using confocal microscopy. The number and size of adipocytes per tissue section were calculated using ImageJ, Prism, and SPSS software. Post-irradiated human SMG displayed high collagen deposition, disorganized cell junctions, and an increased number of adipocytes as compared with non-irradiated controls. These findings are important to improve our understanding of the individual risk and variation in radiation-related salivary gland dysfunction.

Disruption of cell-cell junctions and induction of pathological cytokines in the retinal pigment epithelium of light-exposed mice.

PURPOSE: To elucidate the influences of light exposure on the retinal pigment epithelium (RPE) in vivo that may be involved in the pathogenesis of AMD. METHODS: Six- to 7-week-old BALB/c mice were exposed to light at 2000 lux for 3 hours. Flat-mount RPE samples were immunostained with anti-ZO-1 antibody for evaluating tight junction, anti-N-cadherin, and anti-ß-catenin antibodies for adherens junction, and stained with phalloidin for actin cytoskeleton. The reactive oxygen species (ROS) level was measured using DCFH-DA; Rho-associated coiled-coil forming kinase (ROCK) activity was by ELISA. Cytokine expression was analyzed by real-time RT-PCR and/or ELISA in the RPE-choroid, and macrophage recruitment was by real-time RT-PCR and immunohistochemistry. Either an antioxidant, N-Acetyl-L-cysteine (NAC), or a ROCK inhibitor, Y-27632, were administered to analyze the roles of ROS and ROCK activation, respectively. RESULTS: Light exposure disrupted staining patterns of tight junctions, adherens junctions, and actin cytoskeleton in the RPE, where ROS was elevated. However, NAC treatment avoided the RPE changes, reducing ROS. ROCK activity increased after light exposure was suppressed by NAC, and the structural disruptions were suppressed by Y-27632. The levels of MCP-1, CCL11, and IL-6 increased after light exposure were suppressed by NAC. Light-induced MCP-1 and IL-6 were suppressed by Y-27632. Macrophage recruitment after light exposure was also suppressed either by NAC or Y-27632. CONCLUSIONS: Light exposure induced ROS and Rho/ROCK activation, which caused disruption of cell-cell junctions (tight junctions and adherens junctions) and actin cytoskeleton, the RPE's barrier structure, and induced AMD-associated pathological changes in the RPE-choroid.

Short term effects of gamma radiation on endothelial barrier function: uncoupling of PECAM-1.

A limiting factor in the treatment of cancer with radiotherapy is the damage to surrounding normal tissue, particularly the vasculature. Vessel pathologies are a major feature of the side effects of radiotherapy and little is known about early events that could initiate subsequent diseases. We tested the hypothesis that gamma radiation has early damaging effects on the human endothelial barrier. Two models were used; Human Brain Microcapillary Endothelial Cells (HBMEC), and Human Umbilical Vein Endothelial Cells (HUVEC). Endpoints included Trans-Endothelial Electrical Resistance (TEER), barrier permeability to 10 kDa and 70 kDa tracer molecules, and the localization of F-actin, and junction proteins and the Platelet Endothelial Cell Adhesion Molecule (PECAM-1). Radiation induced a rapid and transient decrease in TEER at 3 h, with effects also seen at the radiotherapy doses. This dip in resistance correlated to the transient loss of PECAM-1 in discrete areas where cells often detached from the monolayer leaving gaps. Redistribution of PECAM-1 was also seen in 3-D human tissue models. By 6 h, the remaining cells had migrated to reseal the barrier, coincident with TEER returning to control levels. Resealed monolayers contained fewer cells per unit area and their barrier function was weakened as evidenced by an increased permeability over 24 h. This is the first demonstration of a transient and rapid effect of gamma radiation on human endothelial barriers that involves cell detachment and the loss of PECAM-1. Considering the association of cell adhesion molecules with vasculopathies, such an effect has the potential to be clinically relevant to the longer-term effects of radiotherapy.

Microbeam radiation-induced tissue damage depends on the stage of vascular maturation.

PURPOSE: To explore the effects of microbeam radiation (MR) on vascular biology, we used the chick chorioallantoic membrane (CAM) model of an almost pure vascular system with immature vessels (lacking periendothelial coverage) at Day 8 and mature vessels (with coverage) at Day 12 of development. METHODS AND MATERIALS: CAMs were irradiated with microplanar beams (width, ∼25 µm; interbeam spacing, ∼200 µm) at entrance doses of 200 or 300 Gy and, for comparison, with a broad beam (seamless radiation [SLR]), with entrance doses of 5 to 40 Gy. RESULTS: In vivo monitoring of Day-8 CAM vasculature 6 h after 200 Gy MR revealed a near total destruction of the immature capillary plexus. Conversely, 200 Gy MR barely affected Day-12 CAM mature microvasculature. Morphological evaluation of Day-12 CAMs after the dose was increased to 300 Gy revealed opened interendothelial junctions, which could explain the transient mesenchymal edema immediately after irradiation. Electron micrographs revealed cytoplasmic vacuolization of endothelial cells in the beam path, with disrupted luminal surfaces; often the lumen was engorged with erythrocytes and leukocytes. After 30 min, the capillary plexus adopted a striated metronomic pattern, with alternating destroyed and intact zones, corresponding to the beam and the interbeam paths within the array. SLR at a dose of 10 Gy caused growth retardation, resulting in a remarkable reduction in the vascular endpoint density 24 h postirradiation. A dose of 40 Gy damaged the entire CAM vasculature. CONCLUSIONS: The effects of MR are mediated by capillary damage, with tissue injury caused by insufficient blood supply. Vascular toxicity and physiological effects of MR depend on the stage of capillary maturation and appear in the first 15 to 60 min after irradiation. Conversely, the effects of SLR, due to the arrest of cell proliferation, persist for a longer time.

Effects of prolonged hypobaric hypoxia on carotid nerve endings and glomus cells. Changes in intercellular coupling.

Carotid bodies were removed from anesthetized rats kept under normobaric (640 Torr) and hypobaric conditions (380 Torr for 2-3 weeks). Slices (100-150 microm) of the organ were viewed under an inverted microscope for simultaneous stimulation and recording of coupled glomus cells and carotid nerve endings. The latter were identified by their more negative Em, high input resistance (Ro) and time-dependent rectification in response to negative current pulses. Also, when nerve endings had an Em more negative than -40 mV showed spontaneous activity in the form of mini-receptor potentials (mrps). Glomus cells had less negative Em and lower Ro. Prolonged hypobaric hypoxia did not change the Em of nerve endings and glomus cells. However, in both structures, Ro increased. Also, the mrps became smaller and occurred less frequently. Intercellular coupling was recognized when currents applied to one cell spread to adjoining ones. In the case of glomus cells (GC/GC coupling), it was mostly resistive and bidirectional. Coupling between nerve endings and glomus cells was more complex, When a glomus cell was stimulated, current spread to the nerve ending (GC/NE coupling) was similar in magnitude (2-3%) to coupling between GCs. However, when NE was stimulated current spread to GC (NE/GC coupling) was minimal (less than 0.1%) and transient (capacitive). Nerve endings were also bidirectionally and capacitively coupled (NE/NE coupling) with a median of 2,8%. Intracellularly injected Lucifer Yellow or Alexa 488 diffused to neighboring structures. Prolonged hypobaric hypoxia significantly tightened coupling modes GC/NE, NE/GC, and NE/NE but reduced GC/GC coupling. Tighter coupling was accompanied by lower coupling resistance, and the opposite occurred when intercellular coupling decreased. Increased GC/NE and reduced GC/GC coupling during hypobaric hypoxia may be partly responsible for the increased reactivity of these receptors under this condition.

Bystander cell proliferation is modulated by the number of adjacent cells that were exposed to ionizing radiation.

BACKGROUND: Direct cell-to-cell contact appears to be a prerequisite for the proliferative response of bystander WB-F344 cells co-cultured with irradiated cells; however, neither gap junctional intercellular communication nor long-range factors released into the medium appear to be involved (Cytometry 2003;56A:71-80). The present work investigated whether the proliferative bystander response depends on the number of irradiated cells (cells exposed to external gamma-rays or cells exposed to short-range beta-particles emitted by DNA-incorporated (3)H-thymidine) that are adjacent to unirradiated bystander cells. METHODS: Subconfluent monolayers of rat liver epithelial cells (WB-F344) were incubated in the presence of (methyl-(3)H)thymidine at a concentration of 5.8 kBq/ml for 18 h. Radiolabeled cells containing 0.7 x 10(-3) Bq/cell (absorbed dose: 0.14 Gy) were plated together with unlabeled cells in proportions of 6% and 94%, 12% and 88%, 25% and 75%, 50% and 50%, and 75% and 25%, respectively, keeping constant the total number of plated cells. In a parallel experiment, cells acutely exposed to 5 Gy of (137)Cs gamma-rays were plated with unirradiated cells in the same proportions. In both experiments, cells were co-cultured for 24 h followed by a flow cytometric study of their proliferation. The two cell populations in the co-cultures were distinguished by staining one population with carboxyfluorescein diacetate, succinimidyl ester, which metabolizes intracellularly. RESULTS: Increasing the fraction of irradiated cells relative to unirradiated bystander cells led to an increase in proliferation of bystander cells. Specifically, in co-cultures in which irradiated cells were initially mixed with unirradiated cells in proportions of 50% and 50% and of 75% and 25%, respectively, bystander cells showed a statistically significant increase of their proliferation compared with the controls. CONCLUSIONS: The proliferative response of WB-F344 bystander cells is modulated by the number of adjacent cells that are exposed to ionizing radiation from external gamma-rays or intracellularly emitted (3)H beta-particles.

Functional and structural alterations of epithelial barrier properties of rat ileum following X-irradiation.

Irradiation of the digestive system leads to alterations of the small intestine. We have characterized the disruption of the barrier integrity in rat ileum from 1 to 14 days following irradiation ranging from 6 to 12 Gy. The intestinal permeability to 14C-mannitol and 3H-dextran 70 000 was measured in vitro in Ussing chambers. In parallel to these functional studies, immunohistochemical analyses of junctional proteins (ZO-1 and beta-catenin) of ileal epithelium were performed by confocal microscopy. Irradiation with 10 Gy induced a marked decrease in epithelial tissue resistance at three days and a fivefold increase in mannitol permeability, without modifications of dextran permeability. A disorganization of the localization for ZO-1 and beta-catenin was also observed. At 7 days after irradiation, we observed a recovery of the organization of junctional proteins in parallel to a return of intestinal permeability to control value. In addition to these time-dependent effects, a gradual effect on epithelial integrity of the radiation doses was observed 3 days after irradiation. This study shows a disruption of the integrity of the intestinal barrier in rat ileum following abdominal X-irradiation, depending on the time postirradiation and on the delivered dose. The loss of barrier integrity was characterized by a disorganization of proteins of tight and adherent junctions, leading to increased intestinal permeability to mannitol.

Role of gap junctional intercellular communication in radiation-induced bystander effects in human fibroblasts.

Involvement of gap junctional intercellular communication (GJIC) in bystander responses of confluent human fibroblasts irradiated with a carbon-ion beam was investigated. It was found that the lower the radiation dose, the higher the yield of radiation-induced micronuclei per nuclear traversal, suggesting the existence of bystander effects. This low-dose sensitivity was increased when GJIC was enhanced by treating cells with 8-Br-cAMP, but it was partly reduced by treating cells with DMSO, an effective scavenger of reactive oxygen species (ROS). Moreover, no low-dose sensitivity was observed when cells were treated with 100 micro M lindane, an inhibitor of GJIC. The survival of irradiated cells was increased by DMSO but was not influenced significantly by cAMP or lindane. On the other hand, G(1)-phase arrest was detected in the irradiated cells, and it was enhanced by cAMP. In contrast, this arrest was reduced or almost eliminated by DMSO or lindane, respectively, even when cells were irradiated with such a high dose that each cell received five nuclear traversals on average. Thus the bystander responses occurred after both low-dose and relatively high-dose irradiation. Our results indicated that both GJIC and ROS contributed to the radiation-induced bystander effect, but gap junctional channels might play an essential role by modulating the release of radiation-induced signaling factors.

Low power millimeter wave irradiation exerts no harmful effect on human keratinocytes in vitro.

Low power millimeter wave (LP-MW) irradiation has been successfully used in clinical practice as an independent and/or supplemental therapy in patients with various diseases. It is still not clear, however, whether exposed skin is directly affected by repeated LP-MW irradiation and whether cells of the epidermis can be activated by the absorbed energy. Keratinocytes, the most numerous component of the epidermis are believed to manifest functional responses to physical stimuli. In this study we analyzed whether LP-MW irradiation modulated the production of chemokines, including RANTES and IP-10 of keratinocytes in vitro. We also investigated whether LP-MW irradiation induces a heat stress reaction in keratinocytes, and stimulates heat shock protein 70 (Hsp70) production. Vital staining of keratinocytes with carboxyfluorescein succinimidyl ester and ethidium bromide was used to analyze the MW effect on the viability of adherent cells. In addition, we studied the effect of LP-MW irradiation on intercellular gap junctional communication in keratinocyte monolayers by Lucifer yellow dye transfer. We found no significant changes in constitutive RANTES and inducible IP-10 production following LP-MW irradiation. LP-MW exposure of keratinocyte monolayers did not alter Hsp70 production, unlike exposure to higher power MWs (HP-MW) or hyperthermia (43 degrees C; 1 h). LP-MW irradiation and hyperthermia did not alter the viability of adherent keratinocytes, while HP-MW irradiation induced cellular damage within the beam area. Finally, we found no alteration in the gap junctional intercellular communication of keratinocytes following LP-MW irradiation, which on the other hand, was significantly increased by hyperthermia. In summary, we detected no harmful effect of LP-MW irradiation on both keratinocyte function and structure in vitro, although these cells were sensitive to higher MW power that developed heat stress reaction and cellular damage. Our results provide further evidence that LP-MW irradiation does not induce evidence of skin inflammation or keratinocyte damage and that its clinical application appears to be safe.

Cell culture dosimetry for low-frequency magnetic fields.

Calculations of the current density and electric field distributions induced in cell cultures by an applied low-frequency magnetic field have assumed that the medium is uniform. This paper calculates these distributions for a more realistic, inhomogeneous, anisotropic model in which the cells are regarded as conducting squares surrounded by insulating membranes. Separate parameters are used to specify the resistivities of the cell interior, the cell membrane parallel to its surface, the cell membrane perpendicular to its surface, and the intercellular junction parallel to the membrane. The presence of gap junctions connecting the interiors of adjacent cells is also considered. For vertical applied magnetic fields, the induced currents and field distributions may deviate considerably from the homogeneous medium model if there is sufficiently tight binding of the cells to each other. The presence of gap junctions can produce relatively large transmembrane electric fields or intracellular current densities. These considerations are generally less important for horizontal applied fields. A simple microscopic model of the cell surface is also discussed.

Effects of ultraviolet radiation on intercellular communication in V79 Chinese hamster fibroblasts.

The effects of ultraviolet (UV) radiation on gap junctional intercellular communication (GJIC) in V79 Chinese hamster fibroblasts were studied by means of a dye transfer assay. Intercellular communication was shown to be altered by UVB (297/302 nm) and UVA (365 nm) radiation, the effect depending on the wavelength of exposure and time between irradiation and microinjection of the dye in the dye transfer assay. Exposure to 297/302 nm radiation induced a reduction in intercellular communication 6 min after exposure. Incubation of the cells post-irradiation reversed the inhibition of GJIC. From 2 to 24 h after exposure an increase in GJIC over the control cells was seen, with a maximum at 8 h post-irradiation. UVA (365 nm) radiation, on the other hand, induced an increase in the intercellular communication 6 min after irradiation. Incubation of the cells post-irradiation led to a decrease in the number of communicating cells, with a minimum seen 4 h after exposure. The reduction in communication observed after exposure to UVB and UVA was not correlated with similar modifications in the gap junction protein connexin43 as found when exposing the cells to the tumour promoter 12-O-tetradecanoyl-phorbol-13-acetate. For the higher fluences of UVA, a decrease in immunorecognizable connexin43 was seen, concomitant with a markedly increased background of higher mol. wt compounds. This may be due to UVA-induced crosslinking of connexin43. No correlation was found between changes in communication induced by UV radiation and levels of cyclic AMP.

Up-regulation of the connexin43+ gap junction network in haemopoietic tissue before the growth of stem cells.

The early developmental stages of haemopoiesis are thought to be regulated by paracrine growth factors and by the haemopoietic environment. Are gap junctions involved here? Gap junctions are structures in cell membranes allowing the direct transfer of ions and small molecules between adjacent cells and are known to be involved in development. We have found that although connexin43 gap junctions are rare (0.00016 +/- 0.0002/microns2 tissue) in normal adult mouse marrow their expression is 80-fold higher (0.0292 +/- 0.0147/microns2) in neonatal marrow. One difference between neonatal and adult haemopoietic tissue is that in the latter more haemopoietic cells are dividing. To test if more gap junctions were due to increased division we altered adult blood-formation by mobilizing or destroying end cells--granulocytes and red cells--or by forcing stem cells to divide by making them regenerate an ablated blood-forming system. Mobilizing end cells had no effect on the number or distribution of gap junctions in marrow but forced stem cell division caused a 100-fold increase in gap junction expression and did so before any recognizable haemopoietic cells formed. There were greater than normal numbers of gap junctions in radio-protected adult mouse marrow. The cells coupled by gap junctions are TE-7+ mesodermally derived fibroblasts, STRO-1+ stromal cells, and CD45+ and CD34+ haemopoietic cells. We propose that there is a latent network of Cx43+ gap junctions in normal quiescent marrow. In response to events that call for active division of stem cells this network is amplified and coupled to haemopoietic stem cells, perhaps enabling them to divide.

Effects of modulated and continuous microwave irradiation on pyroantimonate precipitable calcium content in junctional complex of mouse small intestine.

The pyroantimonate precipitable calcium content of intestinal epithelial cells was investigated in mice following total body irradiation with 2450 MHz continuous and low frequency (16 Hz) square modulated waves. In the control animals the reaction products appeared in the intercellular space of adjacent cells including intermediate junctions and desmosomes and were absent in the area of tight junctions. Immediately after low frequency modulated microwave irradiation at 0.5 and 1mW/cm2 power densities, a rapid distribution of pyroantimonate precipitable calcium content was observed. The pyroantimonate deposits were located on the cytoplasmic side of lateral membrane, in the area of junctional complex, including tight junction, and in other parts of lateral plasma membrane. These changes were reversible and 24 hours after the irradiation the distribution of pyroantimonate deposits was similar to the control. Continuous waves with same energy not altered the distribution of precipitable calcium. We conclude the low frequency modulated microwave irradiation can modify the calcium distribution without heat effects.

Morphological and histochemical changes in intercellular junctional complexes in epithelial cells of mouse small intestine upon X-irradiation: changes of ruthenium red permeability and calcium content.

Changes of calcium-content and permeability of tight junction following X-irradiation were investigated in mouse intestinal epithelial cells by electron microscopy. In the control animals the lower parts of tight junctional area as well as the other junctional elements and the intercellular space are labeled by pyroantimonate precipitates, which contain calcium as revealed by electron spectroscopy and electron energy loss spectrometry. X-irradiation, parallel with morphological changes, lead to rapid decrease of pyroantimonate precipitable calcium content and increase of the permeability of tight junctions indicated by the penetration of ruthenium red into the intercellular space. These changes were readily reversible following 0,5 Gy doses of irradiation however, they persisted up to 24 hours following 5 Gy irradiation. We conclude that irradiation at the applied doses can transiently destabilize the tight junctions in the epithelial layer of the small intestine, presumably through a calcium dependent mechanism.

[The effect of He-Ne laser radiation on the adhesive properties of the cell membrane]. / Vliianie izlucheniia He-Ne lazera na adgezivnye svoistva kletochnoi membrany.

Changes in the number of individual cells and cellular complexes after a standard dispergation procedure were used as a criterion for evaluating the strength of the cellular contacts at various time-points after the irradiation of HeLa monolayers with a He-Ne laser (100 J/m2, 10 W/m2, 10 s). The per cent of cellular complexes increased after the irradiation, being maximal (19.5 +/- 0.6) at 30 minutes of post-irradiation, and then decreased to the control level (12.1 +/- 0.5). Per cent of cellular complexes increased again at longer intervals (90-180 min) after the irradiation.

Modulation of connexon densities in gap junctions of horizontal cell perikarya and axon terminals in fish retina: effects of light/dark cycles, interruption of the optic nerve and application of dopamine.

In the fish retina, connexon densities of gap junctions in the outer horizontal cells are modulated in response to different light or dark adaptation times and wavelengths. We have examined whether the connexon density is a suitable parameter of gap junction coupling under in situ conditions. Short-term light adaptation evoked low connexon densities, regardless of whether white or red light was used. Short-term dark adaptation evoked high connexon densities; this was more pronounced in the axon terminal than in perikaryal gap junctions. Under a 12 h red light/12 h dark cycle, a significant difference in connexon densities between the light and the dark period could be established in the gap junctions of the perikarya and axon terminals. Under a white light/dark cycle, only the gap junctions of axon terminals showed a significant difference. Crushing of the optic nerve resulted in an increase in connexon densities; this was more pronounced in axon terminals than in perikarya. Dopamine injected into the right eye of white-light-adapted animals had no effect. However, dopamine prevented the effect of optic-nerve crushing on connexon density. The reaction of axon-terminal gap junctions to different conditions thus resembles that of perikaryal gap junctions, but is more intense. Axon terminals are therefore thought to play an important role in the adaptation process.