Extensive Gap Junctions Research Articles

The Protective Role of L-Cysteine in the Regulation of Blood-Testis Barrier Functions-A Brief Review.

Blood-testis barrier (BTB) genes are crucial for the cellular mechanisms of spermatogenesis as they protect against detrimental cytotoxic agents, chemicals, and pathogens, thereby maintaining a sterile environment necessary for sperm development. BTB proteins predominantly consist of extensive tight and gap junctions formed between Sertoli cells. These junctions form a crucial immunological barrier restricting the intercellular movement of substances and molecules within the adluminal compartment. Epithelial tight junctions are complex membrane structures composed of various integral membrane proteins, including claudins, zonula occludens-1, and occludin. Inter-testicular cell junction proteins undergo a constant process of degradation and renewal. In addition, the downregulation of genes crucial to the development and preservation of cell junctions could disrupt the functionality of the BTB, potentially leading to male infertility. Oxidative stress and inflammation may contribute to disrupted spermatogenesis, resulting in male infertility. L-cysteine is a precursor to glutathione, a crucial antioxidant that helps mitigate damage and inflammation resulting from oxidative stress. Preclinical research indicates that L-cysteine may offer protective benefits against testicular injury and promote the expression of BTB genes. This review emphasizes various BTB genes essential for preserving its structural integrity and facilitating spermatogenesis and male fertility. Furthermore, it consolidates various research findings suggesting that L-cysteine may promote the expression of BTB-associated genes, thereby aiding in the maintenance of testicular functions.

Glycogen in retinal horizontal cells of the African mud catfish Clarias gariepinus (Burchell, 1822) and its physiological significance

This paper reports on glycogen store in the retinal horizontal cells (HC) of the African mud catfish Clarias gariepinus, as seen by histochemical reaction with periodic acid Schiff (PAS) and transmission electron microscopy in light- as well as dark-adapted state. Glycogen is abundant in the large somata and less in their axons, characterised ultrastructurally by many microtubules and extensive gap junctions interconnecting them. There was no apparent difference in glycogen content in HC somata between light- and dark adaptation, but the axons clearly showed absence of glycogen in dark condition. The HC somata (presynaptic) make synapses with dendrites in the outer plexiform layer. Müller cell inner processes, which contain more densely packed glycogen, invest the HC. Other cells of the inner nuclear layer do not show any appreciable content of glycogen. Rods, but not cones, contain abundant glycogen in their inner segments and synaptic terminals. It is likely that glycogen is used as energy substrate in hypoxia for this species that dwell muddy aquatic environment with low oxygen content. They appear to have high energy demand, and a high glycogen content in HC could act as a ready source to fulfil physiological processes, like microtubule-based transport of cargo from the large somata to axons and the maintenance of electrical activities across the gap junctions between the axonal processes. It is also likely that they can supplement glucose to the neighbouring inner nuclear layer neurons, which are clearly devoid of glycogen.

Tubuloglomerular Feedback Synchronization in Nephrovascular Networks.

To perform their functions, the kidneys maintain stable blood perfusion in the face of fluctuations in systemic BP. This is done through autoregulation of blood flow by the generic myogenic response and the kidney-specific tubuloglomerular feedback (TGF) mechanism. The central theme of this paper is that, to achieve autoregulation, nephrons do not work as single units to manage their individual blood flows, but rather communicate electrically over long distances to other nephrons via the vascular tree. Accordingly, we define the nephrovascular unit (NVU) to be a structure consisting of the nephron, glomerulus, afferent arteriole, and efferent arteriole. We discuss features that require and enable distributed autoregulation mediated by TGF across the kidney. These features include the highly variable topology of the renal vasculature which creates variability in circulation and the potential for mismatch between tubular oxygen demand and delivery; the self-sustained oscillations in each NVU arising from the autoregulatory mechanisms; and the presence of extensive gap junctions formed by connexins and their properties that enable long-distance transmission of TGF signals. The existence of TGF synchronization across the renal microvascular network enables an understanding of how NVUs optimize oxygenation-perfusion matching while preventing transmission of high systemic pressure to the glomeruli, which could lead to progressive glomerular and vascular injury.

Retinal Waves Modulate an Intraretinal Circuit of Intrinsically Photosensitive Retinal Ganglion Cells.

Before the maturation of rod and cone photoreceptors, the developing retina relies on light detection by intrinsically photosensitive retinal ganglion cells (ipRGCs) to drive early light-dependent behaviors. ipRGCs are output neurons of the retina; however, they also form functional microcircuits within the retina itself. Whether ipRGC microcircuits exist during development and whether they influence early light detection remain unknown. Here, we investigate the neural circuit that underlies the ipRGC-driven light response in developing mice. We use a combination of calcium imaging, tracer coupling, and electrophysiology experiments to show that ipRGCs form extensive gap junction networks that strongly contribute to the overall light response of the developing retina. Interestingly, we found that gap junction coupling was modulated by spontaneous retinal waves, such that acute blockade of waves dramatically increased the extent of coupling and hence increased the number of light-responsive neurons. Moreover, using an optical sensor, we found that this wave-dependent modulation of coupling is driven by dopamine that is phasically released by retinal waves. Our results demonstrate that ipRGCs form gap junction microcircuits during development that are modulated by retinal waves; these circuits determine the extent of the light response and thus potentially impact the processing of early visual information and light-dependent developmental functions. Light-dependent functions in early development are mediated by intrinsically photosensitive retinal ganglion cells (ipRGCs). Here we show that ipRGCs form an extensive gap junction network with other retinal neurons, including other ipRGCs, which shapes the retina's overall light response. Blocking cholinergic retinal waves, which are the primary source of neural activity before maturation of photoreceptors, increased the extent of ipRGC gap junction networks, thus increasing the number of light-responsive cells. We determined that this modulation of ipRGC gap junction networks occurs via dopamine released by waves. These results demonstrate that retinal waves mediate dopaminergic modulation of gap junction networks to regulate pre-vision light responses.

A tale of two neurotransmitters.

Amacrine cells are a diverse set of local circuit neurons of the inner retina, and they all release either GABA or glycine, amino acid neurotransmitters that are generally inhibitory. But some types of amacrine cells have another function besides inhibiting other neurons. One glycinergic amacrine cell, the Aii type, excites a subset of bipolar cells via extensive gap junctions while inhibiting others at chemical synapses. Many types of GABAergic amacrine cells also release monoamines, acetylcholine, or neuropeptides. There is now good evidence that another type of amacrine cell releases glycine at some of its synapses and releases the excitatory amino acid glutamate at others. The glutamatergic synapses are made onto a subset of retinal ganglion cells and amacrine cells and have the asymmetric postsynaptic densities characteristic of central excitatory synapses. The glycinergic synapses are made onto other types of ganglion cells and have the symmetric postsynaptic densities characteristic of central inhibitory synapses. These amacrine cells, which contain vesicular glutamate transporter 3, will be the focus of this brief review.

Cx32 and Cx47 mediate oligodendrocyte:astrocyte and oligodendrocyte:oligodendrocyte gap junction coupling

In addition to the extensive gap junction coupling between astrocytes themselves, oligodendrocytes are thought to be exclusively coupled to astrocytes (O:A coupling) via heterotypic gap junctions composed of Cx47:Cx43 and Cx32:Cx30. We used fluorescent dyes to examine functional coupling in acute slices from the cerebra of mice lacking Cx32 and/or Cx47. In the corpus callosum, unexpectedly, oligodendrocytes appeared to be directly and exclusively coupled to other oligodendrocytes (O:O coupling), and electron microscopy revealed gap junctions between adjacent oligodendrocytes. O:O coupling was more affected in mice lacking Cx32 than in mice lacking Cx47. In the neocortex, oligodendrocytes appeared to be directly and exclusively coupled to astrocytes; Cx47, but not Cx32, was required for O:A coupling.

The light-induced reduction of horizontal cell receptive field size in the goldfish retina involves nitric oxide

Horizontal cells of the vertebrate retina have large receptive fields as a result of extensive gap junction coupling. Increased ambient illumination reduces horizontal cell receptive field size. Using the isolated goldfish retina, we have assessed the contribution of nitric oxide to the light-dependent reduction of horizontal cell receptive field size. Horizontal cell receptive field size was assessed by comparing the responses to centered spot and annulus stimuli and from the responses to translated slit stimuli. A period of steady illumination decreased the receptive field size of horizontal cells, as did treatment with the nitric oxide donor (Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate (100 μM). Blocking the endogenous production of nitric oxide with the nitric oxide synthase inhibitor, N(G)-nitro-L-arginine methyl ester (1 mM), decreased the light-induced reduction of horizontal cell receptive field size. These findings suggest that nitric oxide is involved in light-induced reduction of horizontal cell receptive field size.

Abstract 1416: IGF-1 Gene Transfer Promotes Connexin-43 Expression and Enhances Integration of Bone Marrow Stem Cells in the Infarcted Heart

For functional benefits, bone marrow stem cells should engraft and develop functional syncitium with the host myocytes in the infarcted heart. We report that IGF-1 overexpression significantly enhances connexin-43 (Cx-43) in mesenchymal stem cells (MSCs) which promotes their survival and functional integration with host myocardium post-engraftment. IGF-1 gene transduced MSCs ( IGF-1 MSCs) expressed higher IGF-1 ( p < 0.001 ) as compared with GFP gene transduced cells ( GFP MSCs). After 8h anoxia, MSCs, H2C9 and endothelial cells treated with IGF-1 MSCs conditioned medium ( IGF-1 CM) showed higher survival ( p < 0.001 vs GFP MSCs conditioned medium ( GFP CM) supported by higher Akt activation which was abolished by wortmannin. Immunodetection showed Cx-43 plaques in the peripheral areas besides punctate distribution in the cytoplasm around the nucleus in IGF-1 MSCs and IGF-1 CM treated MSCs whereas GFP MSCs and GFP CM treated MSCs showed Cx-43 expression in regions of intimate cell to cell contact only. IGF-1 overexpression or IGF-1 CM treatment of MSCs also induced higher level Akt and p27 activation, and Cx-43 expression as compared with GFP MSCs ( p = 0.02 ) which was abolished by wortmannin. For in vivo studies, 70 μ l DMEM without cells (group-1) or containing 1x10 6 GFP MSC (group-2) or IGF-1 MSC (group-3) were injected intramyocardially in female rat model of coronary artery ligation (n=16/group). The animals were harvested on 7 days and 6 weeks after cell engraftment. FISH and sry -gene analysis on 7 day showed extensive survival of the male donor cells in the heart. Real-time PCR and Western blot on the heart tissue showed higher level of Cx-43 and activation of p27 in group-3 ( p < 0.05 vs group-2). The number of TUNEL + cells was lower in group-3 ( p = 0.01 vs group-2). Immunostaining for α -sarcomeric actin and Cx-43 showed extensive myogenic differentiation of IGF-1 MSCs and gap junction formation between adjacent neofibers. Indices of heart function including ejection fraction (63.05±1.37%) and fractional shortening (28.54±0.92%) were improved in group-3 ( p < 0.001 vs group-2 ) . IGF-1 enhances Cx-43 expression in MSCs and promotes their engraftment and functional integration in the heart and improves heart function.

Endothelial coordination of cerebral vasomotion via myoendothelial gap junctions containing connexins 37 and 40

Control of cerebral vasculature differs from that of systemic vessels outside the blood-brain barrier. The hypothesis that the endothelium modulates vasomotion via direct myoendothelial coupling was investigated in a small vessel of the cerebral circulation. In the primary branch of the rat basilar artery, membrane potential, diameter, and calcium dynamics associated with vasomotion were examined using selective inhibitors of endothelial function in intact and endothelium-denuded arteries. Vessel anatomy, protein, and mRNA expression were studied using conventional electron microscopy high-resolution ultrastructural and confocal immunohistochemistry and quantitative PCR. Membrane potential oscillations were present in both endothelial cells and smooth muscle cells (SMCs), and these preceded rhythmical contractions during which adjacent SMC intracellular calcium concentration ([Ca(2+)](i)) waves were synchronized. Endothelium removal abolished vasomotion and desynchronized adjacent smooth muscle cell [Ca(2+)](i) waves. N(G)-nitro-l-arginine methyl ester (10 microM) did not mimic this effect, and dibutyryl cGMP (300 muM) failed to resynchronize [Ca(2+)](i) waves in endothelium-denuded arteries. Combined charybdotoxin and apamin abolished vasomotion and depolarized and constricted vessels, even in absence of endothelium. Separately, (37,43)Gap27 and (40)Gap27 abolished vasomotion. Extensive myoendothelial gap junctions (3 per endothelial cell) composed of connexins 37 and 40 connected the endothelial cell and SMC layers. Synchronized vasomotion in rat basilar artery is endothelium dependent, with [Ca(2+)](i) waves generated within SMCs being coordinated by electrical coupling via myoendothelial gap junctions.

In differentiating prefusion myoblasts connexin43 gap junction coupling is upregulated before myoblast alignment then reduced in post-mitotic cells

Previously we have shown that during in vivo muscle regeneration differentiating rat primary myoblasts transiently upregulate connexin43 (Cx43) gap junctions and leave cell cycle synchronously. Here, we studied the temporal regulation of Cx expression in relation to functional dye coupling in allogenic primary myoblast cultures using western blotting, immuno-confocal microscopy and dye transfer assays. As in vivo, Cx43 was the only Cx isotype out of Cx26, 32, 37, 40, 43 and 45 found in cultured rat myoblasts by immunostaining. Cultured myoblasts showed similar temporal regulation of Cx43 expression and phenotypic maturation to those regenerating in vivo. Cx43 protein was progressively upregulated in prefusion myoblasts, first by the cytoplasmic assembly in sparse myoblast meshworks and then in cell membrane particles in aligned cells. Dye injection using either Lucifer Yellow alone, Cascade Blue with a non-junction permeant FITC-dextran revealed an extensive gap junction coupling between the sparse interacting myoblasts and a reduced communication between the aligned, but still prefused cells. The aligned myoblasts, uniformly upregulate p21(waf1/cip1) and p27(kip1) cell cycle control proteins. Taken together, in prefusion myoblasts less membrane-bound Cx43 was found to mediate substantially more efficient dye coupling in the growing cell fraction than those in the aligned post-mitotic myoblasts. These and our in vivo results in early muscle differentiation are consistent with the role of Cx43 gap junctions in synchronizing cell cycle control of myoblasts to make them competent for a coordinated syncytial fusion.

Transient upregulation of connexin43 gap junctions and synchronized cell cycle control precede myoblast fusion in regenerating skeletal muscle in vivo

The spatio-temporal expression of gap junction connexins (Cx) was investigated and correlated with the progression of cell cycle control in regenerating soleus muscle of Wistar rats. Notexin caused a selective myonecrosis followed by the complete recapitulation of muscle differentiation in vivo, including the activation, commitment, proliferation, differentiation and fusion of myogenic cells. In regenerating skeletal muscle, only Cx43 protein, out of Cx-s 26, -32, -37, -40, -43 and -45, was detected in desmin positive cells. Early expression of Cx43 in the proliferating single myogenic progenitors was followed by a progressive upregulation in interacting myoblasts until syncytial fusion, and then by a rapid decline in multinucleate myotubes. The significant upregulation of Cx43 gap junctions in aligned myoblasts preceding fusion was accompanied by the widespread nuclear expression of cyclin-dependent kinase inhibitors p21(waf1/Cip1) and p27(kip1) and the complete loss of Ki67 protein. The synchronized exit of myoblasts from the cell cycle following extensive gap junction formation suggests a role for Cx43 channels in the regulation of cell cycle control. The potential of Cx43 channels to stimulate p21(waf1/Cip1) and p27(kip1) is known. In the muscle, proving the involvement of Cx43 in either a direct or a bystander cell cycle regulation requires functional investigations.

Four classes of intercellular channels between glial cells in the CNS.

Astrocytes form extensive gap junctions with other astrocytes and with oligodendrocytes. Junctional communication between CNS glia is likely of critical importance because loss of the gap junction channel-forming proteins, connexins Cx32 and Cx47, result in severe demyelination. However, CNS glia express at least six connexins, and the cellular origins and relationships of these proteins have not been determined. We produced a Cx29 reporter mouse in which the connexin coding sequence was replaced with a histological marker, which was used to demonstrate that Cx29, Cx32, and Cx47 are expressed specifically in oligodendrocytes. To determine the relationships between astrocyte and oligodendrocyte connexins, we used double- and triple-immunofluorescence microscopy using semithin sections (<1 microm) of adult mouse spinal cord. Astrocytes form two distinct classes of gap junctions with each other; those composed of Cx26 and those composed of Cx43 and Cx30. In addition, astrocytes establish two classes of intercellular channels with oligodendrocytes, heterotypic Cx26-Cx32 channels and heterotypic Cx30/Cx43-Cx47 channels that may also be heteromeric. In contrast, Cx29 does not colocalize with any of the other five connexins. The data provide the first in vivo demonstration of heterotypic intercellular channels and reveal an unexpected complexity in the composition of glial gap junctions.

Electrical Synapses Mediate Signal Transmission in the Rod Pathway of the Mammalian Retina

In the retina, AII (rod) amacrine cells are essential for integrating rod signals into the cone pathway. In addition to being interconnected via homologous gap junctions, these cells make extensive heterologous gap junctions with ON-cone bipolar cells (BCs). These gap junctions are the pathway for transfer of rod signals to the ON-system. To investigate the functional properties of these gap junctions, we performed simultaneous whole-cell recordings from pairs of AII amacrine cells and ON-cone bipolar cells in the in vitro slice preparation of the rat retina. We demonstrate strong electrical coupling with symmetrical junction conductance (approximately 1.2 nS) and very low steady-state voltage sensitivity. However, signal transmission is more effective in the direction from AII amacrine cells to ON-cone bipolar cells than in the other direction. This functional rectification can be explained by a corresponding difference in membrane input resistance between the two cell types. Signal transmission has low-pass filter characteristics with increasing attenuation and phase shift for increasing stimulus frequency. Action potentials in AII amacrine cells evoke distinct electrical postsynaptic potentials in ON-cone bipolar cells. Strong and temporally precise synchronization of subthreshold membrane potential fluctuations are commonly observed.

Ultrastructure and blood supply of the tegmentum vasculosum in the cochlea of the duckling

The tegmentum vasculosum of the duckling consists of a highly folded epithelium which extends over the dorsal and lateral walls of the cochlear duct, separating the scala media from the scala vestibuli. This epithelium consists of two distinct cell types, dark cells and light cells, and is well vascularized. The surface of the epithelium is formed by a mosaic of alternating dark and light cells. The goblet-shaped dark cells have an electron-dense, organelle-rich cytoplasm, and are expanded basally by extensive basolateral plasma membrane infoldings, within which are numerous mitochondria. Dark cells are isolated from each other and from the capillaries within the epithelium by intervening light cells. In contrast, columnar light cells exhibit an electron-lucent, organelle-poor cytoplasm and may extend from the underlying capillaries to the endolymphatic surface. Light cells contain abundant, coated endocytic vesicles on their apical surfaces and are bound, apically, to other light cells or to dark cells by tight junctions and desmosomes. Laterally, light cells are linked to each other either by complex, fluid-filled membrane interdigitations or by extensive gap junctions. Plasma membrane interdigitations and obvious, fluid-filled intercellular spaces characterize the lateral borders between light and dark cells. Vascular corrosion casting reveals the three-dimensional anatomy of the cochlear vasculature. A continuous arteriolar loop fed by anterior and posterior cochlear arterioles encircles the cochlear duct. The rich capillary beds of the tegmentum vasculosum are supplied by arching arterioles arising from this loop. These capillaries are the continuous type and are situated primarily within the core of the epithelium or along its border with the scala vestibuli. The structure and blood supply of the tegmentum vasculosum are characteristic of an epithelium involved in active transport.

Epithelial Organization of the Mammalian Lens

To understand the structural organization responsible for lens function, we have studied the three-dimensional arrangement of cells in the lens, and the location and molecular composition of specialized junctions controlling the paracellular and transcellular pathways. The lens is formed by a single layer of polarized cells that elongate along their apical–basal axis from the anterior to the posterior pole to form the cortex, and fold inward at the posterior pole to form the nucleus. The basal surfaces of all cells of the cortex (approximately two thirds of all lens cells) are bathed by the aqueous and vitreous humors. Therefore, their metabolism is not limited by diffusion of nutrients into the avascular lens. The apical surfaces of all cortical fibers are directed toward the interior of the lens, where they form two distinct structures here referred to as the ‘apical interface’ and the ‘modiolus’. The apical interface is located at a point close to the anterior pole, and is formed by the association of the apical surface of anterior cortical cells and the apical surface of cortical fibers extending from the posterior pole. The modiolus is located close to the equator at the lateral edge of the apical interface, and is formed by the tapered apical ends of equatorial cortical fibers. The plasma membrane of cortical cells at the anterior pole are connected through ‘leaky’ tight junctions and small gap junctions. Extensive gap junction plaques composed of connexin43 connect equatorial fibers at the modiolus and posterior cortical fibers at the apical interface. Single cell-to-cell channels composed of connexin46 and connexin50 connect the lateral surfaces of equatorial and posterior cortical fibers. The lateral surfaces of these fibers also contain extensive junctions composed of aquaporin-0. The nucleus is connected to the humors through the paracellular pathway represented by the anterior (apical) and posterior (basal) suture lines. Therefore, the metabolic needs of nuclear fibers cannot be fulfilled by simple diffusion and requires the cell-to-cell pathway formed by specialized junctions. The lateral surfaces of nuclear fibers contain extensive wavy junctions composed of aquaporin-0, probably for the control of the permeability of the paracellular pathway. We propose a simple epithelium model for the lens in which nutrients move into the nucleus through the paracellular pathway represented principally by the suture lines, and the transcellular pathway represented by an extensive network of gap junction plaques composed of connexin43 at the apical surface, and single or small plaques of cell-to-cell channels composed of connexin46 and connexin50 in the lateral surfaces.

Gap junctional intercellular communication and connexin 43 expression in ovarian carcinoma

Objectives: Gap junctions, which are composed of subunits termed connexins, are plasma membrane channels that link the interior of adjacent cells and permit cells to directly exchange small molecules and ions. Loss or dysfunction of gap junctions appears to be important in allowing cancer cells to escape growth regulation. In a previous study we showed that human ovarian surface epithelial cells exhibited extensive gap junctions and expression of connexin 43. These were nearly absent in human ovarian adenocarcinoma cell lines. To ensure that this variation was not artificially produced by culturing techniques, this study evaluated gap junctions and connexin 43 expressions in normal ovaries and in ovarian adenocarcinomas. Study Design: Specimens of normal ovaries and ovarian adenocarcinomas were obtained at the time of surgery and flash-frozen in liquid nitrogen. Connexin 43 immunostaining was performed on all specimens. Results: Among the 11 normal ovaries an average of 59% of the surface epithelium stained positively for connexin 43. In contrast, among the 10 ovarian adenocarcinomas only 19% of each specimen stained positively for connexin 43 ( P = .01). Conclusion: Similar to our studies on human ovarian surface epithelial cells and ovarian adenocarcinoma cell lines, surgical specimens of normal ovary exhibited extensive connexin 43 expression, whereas connexin 43 expression was nearly absent in ovarian adenocarcinomas. It thus appears that the previously reported loss of gap junctions and connexin 43 was actually associated with a neoplastic process, rather than being artificially induced in the laboratory. (Am J Obstet Gynecol 2000;182:999-1000.)

Ultrastructure of the supporting cells in the paratympanic organ of chicken, Gallus gallus domesticus

The paratympanic organ is a specialized sensory organ of birds located in the medial wall of the tympanic cavity. It possesses a sensory epithelium formed by type II hair cells and supporting cells. The supporting cells are tall, narrow units that extend from the basement membrane to the free epithelial surface. They show a fine structure characterized by numerous mitochondria, a conspicuous Golgi complex and a well-developed RER. Moreover, some uncommon structures, probably formed by heaped RER cisternae, are frequently present in the cytoplasm. Adjacent supporting cells are connected by numerous and extensive gap junctions; moreover, small gap junctions between hair cell and supporting cells are to be found. The possible mechanical and metabolical functions of the paratympanic organ supporting cells are discussed. J. Morphol. 236:65–73, 1998. © 1998 Wiley-Liss, Inc.

Ultrastructure of the supporting cells in the paratympanic organ of chicken, Gallus gallus domesticus.

The paratympanic organ is a specialized sensory organ of birds located in the medial wall of the tympanic cavity. It possesses a sensory epithelium formed by type II hair cells and supporting cells. The supporting cells are tall, narrow units that extend from the basement membrane to the free epithelial surface. They show a fine structure characterized by numerous mitochondria, a conspicuous Golgi complex and a well-developed RER. Moreover, some uncommon structures, probably formed by heaped RER cisternae, are frequently present in the cytoplasm. Adjacent supporting cells are connected by numerous and extensive gap junctions; moreover, small gap junctions between hair cell and supporting cells are to be found. The possible mechanical and metabolical functions of the paratympanic organ supporting cells are discussed.

Ultra-structural characteristics of bovine granulosa cells associated with maintenance of oestradiol production in vitro

We investigated whether the maintenance of oestradiol production by bovine granulosa cells (GC) in vitro was related to GC ultra-structure, and studied the effects of inclusion of serum as a cell attachment factor on oestradiol secretion, cell morphology and ultra-structure. Bovine granulosa cells from medium-sized follicles (4–8 mm diameter), in a serum-free (SF) culture system, maintained oestradiol production for 6 days, whereas oestradiol secretion by cells cultured in serum-coated (SC) wells declined rapidly with time, in culture. SF cells formed clumps consisting of two types of cells. Cells within clumps presented a phenotype similar to GC in vivo, being spherical, tightly joined by extensive gap junctions and interdigitated pseudopodia/microvilli, had abundant rough and smooth endoplasmic reticulum (ER) and mitochondria with trabecular cristae. In contrast, cells cultured in either SC wells or in the flattened base of cell clumps from SF cultures were enlarged, containing less rough ER, had fewer mitochondria (which tended to be round) and contained endosome-like structures, morphological characteristics suggestive of early luteinisation.

Efferent fibers and the posteromedial eye of the liphistiid spiderHeptathela kimurai (Araneae: Liphistiomorphae)

The fine structure of the posteromedial eyes of liphistiid spiders, kept under a natural daily photoperiod, were examined by electron microscopy. The posteromedial eye in these spiders is erect with about 110 receptor cells. Under the dioptrics, the somata of the receptor cells were found to be surrounded by nonpigmented cells whose processes were multilayered and attached to each other by extensive gap junctions, septate junctions, and adherens junctions. No processes of nonpigmented cells were observed in the retina, in which the rhabdoms were arranged in a roughly hexagonal network in cross-section and changed in size from day to night. Efferent fibers were observed in the retina. They contained characteristic large, electron-dense granules and small, flattened, clear vesicles. They branched within the retina with varicosities, providing synaptoid contacts with receptor cells. These efferent fibers were presynaptic in relation to the receptor cells. After transformation into the intermediate segment, the receptor cells formed axons, and some gathered together sporadically to pass through a tapetal reflecting layer. Pigmented cells were located in the most lateral portion of the eye. They covered the whole eye and were intercalated with the intermediate segments of the receptor cells. © 1996 Wiley-Liss, Inc.