Membrane ultrastructure at mammalian intercellular junctions

Gap junctions coupling photoreceptor axons in the first optic ganglion of the fly

The first optic ganglion of the fly, the lamina ganglionaris, was investigated with the transmission electron microscope for the purpose of demonstrating possible electronic junctions. Within a cartridge, the six short receptor cell axons R1--R6 are extensively coupled by symmetrical gap junctions. This is mainly seen in the distal third of the first synaptic region where none or only a few lateral branches of the centrally lying L-fibres (L1, L2) penetrate the ring of six short receptor fibre endings. Gap junctions as found between R1--R6 are distinguished morphologically from chemically-mediated synapses by the closely apposed cell membranes. They exhibit only a 2--4 nm extracellular cleft. Unlike the chemical synapse the gap junction in the neuropile of the fly appears structurally symmetrical. No such gap junctions are found either between R-fibres and glial cells, interneurons and glial cells, between glial cells and between interneurones themselves, nor between the parallel long receptor axons R7/8, which bypass the lamina outside the cartridge. In accordance with electrophysiological data, it can now be argued that the six short receptor axons R1--R6 are electrically interconnected by symmetrical gap junctions.

The oligodendrocytic junctional complex

The junctional complex of oligodendrocytes was studied by means of different electron microscopical techniques. This complex is composed of the following junctional membrane formations: 1) tight junctional domains in the oligodendrocytic membrane near the some of the cells, 2) fasciae occludentes or focal tight junctions on the outer oligodendrocytic loop of myelin and on the outermost myelin membrane, 3) gap junctions of considerable size variations, either on membranes near the soma or on peripheral oligodendrocytic processes, and 4) non-paranodal transverse bands. The different types of oligodendrocytic junctions are discussed in terms of their functional implications.

Physiological and morphological evidence for coupling in mouse salivary gland acinar cells

Three experimental techniques were employed to examine coupling between acinar cells of the mouse salivary gland. Passage of DC current pulses via intracellular microelectrodes between neighboring cells showed that small ions could be directly passed from one cell to another. Intracellular iontophoresis of the dye Lucifer Yellow CH into a single cell indicated that small molecules could spread by means of intercellular cytoplasmic bridges througout an acinus and, occasionally, into cells of adjacent acini. Freeze-fracture replicas of acinar cell membranes indicated the presence of gap junctions which were correlated with both electrical and dye coupling experiments. Suggestions are made for the function of direct intercellular exchange in salivary secretory cells. The role of electrical coupling in coordination of the activity of different secretory cell types is discussed as one possible function.

Effect of intercellular communication on the selection of intraspecific human hybrids in HAT and ouabain

Optimal conditions have been determined for selection of hybrids in HAT and ouabain (HOT) from the PEG-mediated fusion of OUAR/HGPRT-/G6PDA and OUAS/HGPRT+/G6PDB human diploid fibroblasts. In addition to the OUARHGPRT+G6PDAB tetraploid hybrids, several other types of HOT-resistant colonies were obtained from these fusions and identified by G6PD isozyme analysis and karyotyping as (1) hybrids contaminated with diploid parental cells, (2) symbiotic mixtures of the two types of parental cells, or (3) spontaneous OUAR mutants. The mechanism for parental cell growth in HOT is most likely the transfer of HAT resistance and/or ouabain resistance through gap junctions formed between resistant and sensitive cells.

Formation of gap junctions by treatment in vitro with potassium conductance blockers

Gap junctions were regularly seen in thin sections of canine tracheal smooth muscle incubated in vitro. Their number was increased in tissued exposed in vitro to either of two potassium conductance blockers, tetraethylammonium (TEA) and 4-aminopyridine (4-AP), and at the same time the muscles became mechanically active, with spontaneous contractions. The presence of gap junctions in this smooth muscle may provide one basis for cell-to-cell coupling, and their increase after TEA- and 4-AP-treatment could account for a decreased junctional resistance between cells, contributing to a longer space constant. However, an increase in gap junctions was not sufficient to change the behavior of trachealis smooth muscle from multiunit to single-unit type. Gap junctions in increased numbers persisted after washout of 4-AP, which caused inhibition of spontaneous contractions, and despite inhibition of the contractile effects of 4-AP by atropine. The rapid induction of gap junction formation was not dependent on de novo synthesis of protein. The fact that the number of gap junctions can be increased by chemical agents has important implications for control of their formation and provides a tool for analysis fo their role in cell-to-cell coupling.

Nexal membrane permeability to anions

The permeability of the septa of the earthworm in the median axon has been calculated for the anions fluorescein and its halogen derivatives. The values ranged from 5.4 X 10(-5) to 4 X 10(-6) cm/s. Previously, the septa had been shown to contain nexuses. By using freeze-fracture material, the surface area of nexus on the septal membranes was determined to be 4.5%, very similar to the percentage of nexus in the intercalated disk of mammalian myocardium. Plasma membrane permeability to these dyes was also calculated and shown to be much less than that of the septal membranes. In addition, an estimate of cytoplasmic binding for each dye was made, and most dyes showed little or no binding with the exception of aminofluorescein.

Cytoplasmic filaments and gap junctions in epithelial cells and myofibroblasts during wound healing

During the healing of an experimental skin wound, epidermal cells and granulation tissue fibroblasts (myofibroblasts) develop an extensive cytoplasmic contactile apparatus. Concurrently, the proportion of epidermal cell surface occupied by gap junctions increases when compared to normal skin, and newly formed gap junctions appear between myofibroblasts; this suggests that epidermal cell migration and granulation tissue contraction are synchronized phenomena.

Membrane structural specialization of the toad urinary bladder revealed by the freeze-fracture technique. III. Location, structure and vasopressin dependence of intramembrane particle arrays

Examination of the toad urinary bladder by freeze-fracture electron microscopy reveals intramembrane particle arrays at a number of membrane sites. An array in which particles are aggregated into closely apposed parallel rows is found in the granular cell luminal membrane of dehydrated toads fixed in situ. These aggregates are structurally indistinguishable from those previously associated with vasopressin exposure in vitro. Aggregates are not found in granular cell luminal membrane in the case of hydrated toads fixed in situ. However, structurally similar arrays are found at low frequency in the membrane of cytoplasmic vacuoles in granular cells and in the plasma membrane of basal cells in both hydrated and dehydrated toads. Aggregates are also present at these sites in control and vasopressin-treated bladders from in vitro experiments. Particle arrays characteristic of gap junctions, desmosomes and hemidesmosomes also occur in the plasma membrane of basal cells. In addition, distinctive square arrays of particles exist in the plasma membrane of the bladder's mesothelium. Although a variety of intramembrane particle arrays exist in the toad urinary bladder, only the occurrence of organized particle aggregates in the luminal membrane of granular cells appears to be associated with vasopressin exposure.

Exocrine pancreas under experimental conditions. IV. Alterations of intercellular junctions between acinar cells following pancreatic duct ligation

Exocrine pancreatic tissue was investigated during various intervals after pancreatic duct ligation. Concomitant to the increase of the intraluminal pressure, alterations are found in the arrangement of the luminal membrane surface and the zonulae occludentes of the acinar cells. The zonulae occludentes exhibit a disarrangement of their strands. The number of strands diminishes and small interruptions as well as large discontinuities of the strands are observed in most regions of the acinar cells. Furthermore, gap junctions are found very infrequently between acinar cells. The ultrastructural alterations of the zonulae occludentes suggest a gradual adaptation to the increasing unilateral pressure. However, a leakage of the paracellular permeability barrier occurs which contributes to the known shunt between the compartments of the pancreatic juice and the interstitial space following pancreatic duct obstruction. The present investigation is a further example of alterations in the paracellular permeability and intercellular communication of epithelial cells under pathological conditions.

Cellular interrelationships in the fetal rabbit testis

The types and patterns of arrangement of membrane interrelationships in the fetal rabbit testis were studied, using coordinated freeze-fracture, lanthanum tracer and standard transmission electron microscopic techniques. The testicular cords contain a mixture of large spherical germ cells and oval to elongated Sertoli cells. Desmosomes are present between germ cells and Sertoli cells and between adjacent Sertoli cells. Tight junctional specializations of the type found between Sertoli cells in the adult are not seen. In freeze-fracture replicas, short strands of particles of two different size populations are found on the surfaces of Sertoli cells. Similar short strands of particles are present on the membranes of peritubular myoid cells. In lanthanum preparations, the tracer passes freely between peritubular cells and through intercellular spaces within the seminiferous cords, indicating lack of a barrier to its passage throughout the testicular tissue. Prominent macular gap junctions similar to those found between adult Leydig cells are readily observed on the surfaces of fetal Leydig cells. The presence of gap junctions in the fetal testis may be important in coordinating the active testosterone production which occurs during this period of development.

A study of communication specificity between cells in culture

We have examined the specificity of communication between cells in culture by co-culturing cells derived from mammalian, avian, and arthropod organisms. Both mammalian and avian culture cells have similar gap junctional phenotypes, while the insect (arthropod) cell lines have a significantly different gap junctional structure. Electrophysiological and ultrastructural methods were used to examine ionic coupling and junctional interactions between homologous and heterologous cell types. In homologous cell systems, gap junctions and ionic coupling are present at a high incidence. Also, heterologous vertebrate cells in co-culture can communicate readily. By contrast, practically no coupling (0-8%) is detectable between heterologous insect cell lines (Homopteran or Lepidopteran) and vertebrate cells (mammalian myocardial or 3T3 cells). No gap junctions have been observed between arthropod and vertebrate cell types, even though the heterologous cells may be separated by less than 10 nm. In additional studies, a low incidence of coupling was found between heterologous insect cell lines derived from different arthropod orders. However, extensive coupling was detected between insect cell lines that are derived from the same order (Homoptera). These observations suggest that there is little or no apparent specificity for communication between vertebrate cells in culture that express the same gap junctional phenotype, while there is a definite communication specificity that exists between arthropod cells in culture.

Membrane alterations during cornification of mammalian squamous epithelia: a freeze-fracture, tracer, and thin-section study

Tight junctions (zonulae occludentes) create a pericellular barrier to the diffusion of large molecules in non-keratinizing mammalian epithelia. However, in cornifying epithelia such as the epidermis, the importance of tight-junctional elements versus secreted intercellular lipid for barrier function is uncertain. In an attempt to resolve this question, we compared membrane structure in the stratum granulosum and stratum corneum of epidermis, esophagus, and vagina of newborn and adult humans and mice under both normal and various experimental conditions. We incubated pieces of epidermis in organ culture and infused tissues with lanthanum or horseradish peroxidase in vivo and in vitro. All were processed for electron microscopy of freeze-fracture replicas or thin sections. Lanthanum seeped outward to the stratum granulosum in all tissues examined--further apical migration was halted by lamellar-body contents in skin. A similar pattern of intercellular lamellar lipid deposition and membrane structure occurred in all epithelia studied. Freeze-fracture replicas of these obstructive regions revealed occasional, incomplete junctional strands (particularly in moist epithelia) and abundant lamellar material, but complete zonulae occludentes were never encountered. A possible relationship between moisture and tight junction formation was further suggested by organ culture experiments during which brief incubations stimulated an increase in the number of junctional strands and diminished numbers of lamellar bodies. We conclude that, in the epithelia studied, the deposition of secreted lamellar body contents forms the barrier to water-soluble tracer loss: tight-junctional elements are either absent or too fragmentary to constitute an effective barrier.

Intercellular junctional complexes of the rat seminiferous tubules: a freeze-fracture study

This paper provides a description of the intercellular junctions in the rat testis, as observed using the freeze fracture technique. These intercellular junctions were categorized into four general types: Sertoli cell tight junctions, myoid cell tight junctions, gap junctions, and "heterogeneous junctions." The Sertoli cell tight junctions had a mean depth of 3.1 micron in the basal to apical direction, and contained 25 to 50 (average: 36) parallel rows of particulate sealing elements. The myoid cell tight junction was neither continuous nor extensive, but focal in nature. Interestingly the sealing elements of this junction, like those of the Sertoli cell tight junction, were quite particulate in nature. Typical gap junctions were observed between Sertoli cells where they were intercalated between the parallel rows of the Sertoli cell tight junction. The most interesting observation was the identification of gap junction-like structures, in various stages of formation, on germ cell membrane fracture faces, both in the basal and adluminal compartments. Lastly, the unusual "heterogeneous junction" was observed on large membrane fracture faces in close proximity to cells in the adluminal compartment, presumably between Sertoli cells. These junctions appeared to consist of both tight and gap junction elements.

Ultrastructure of the blood-aqueous barrier in normal condition and after paracentesis A freeze-fracture study in the rabbit

There is in the ciliary epithelium a barrier which prevents the passage of plasma proteins into the posterior chamber of the eye. The anatomical site of this blood-aqueous barrier is at the zonulae occludentes (tight junctions) located between the lateral plasma-membranes of the nonpigmented epithelial cells. Using the freeze-fracture technique we have studied these junctions in the pars plicata. As in many epithelia, they are formed by an anastomosing network of ridges on the fracture PF face and by a complementary set of furrows on the fracture EF face of plasma membranes. Features of these junctions are the presence of frequent parallel and closely associated double or triple ridges, and a few small gap junctions, associated with tight junctional elements of the zonulae occludentes. We also show that the number of junctional strands (ridges and furrows from apex to base) varies from a few strands to about 15, according to their position around the nonpigmented epithelial cells. These observations suggest that the rabbit's ciliary epithelium is to be classified among the 'tight' or 'very tight' epithelia (Claude and Goodenough, 1973). After paracentesis, we observed no breakdown of the zonulae occludentes. This supports the hypothesis that the site of leakage of the plasma proteins is elsewhere than ciliary epithelium.

Epidermal intercellular relationships during carcinogenesis and cocarcinogenesis as revealed by scanning electron microscopy

Investigations with the scanning electron microscope were carried out on the skin of 80 NMRI mice after treating them with small doses of the carcinogenic substance DMBA and the cocarcinogenic agent TPA, respectively. The results were correlated with histologic, transmission electron microscope and autoradiographic observations. The epidermis of TPA-treated animals was markedly hyperplastic with an orderly arrangement of cell layers. Autoradiographically only the basal cells were heavily labelled. With the scanning and transmission electron microscope a reduced number of intercellular connections and dilatation of the intercellular spaces could be detected. After treatment with DMBA the epidermis was only moderately hyperplastic but severely dysplastic with 3H-thymidine-labelled cells in the upper layers. The most characteristic findings were the loss of the intercellular connections, especially the lateral ones, and a pronounced dilatation of the intercellular spaces. The results obtained with the scanning electron microscope were quantified using morphometrical methods.

Freeze-fracture observations on the membranes and junctions in human prostatic carcinoma and benign prostatic hypertrophy

In human prostatic carcinomatous acini, the columnar cells possessed a loosely organized meshwork of ridges and grooves and many isolated, short, and disorganized strands of tight junctions, unlike those of benign prostatic hypertrophy (BPH), where the tight junctional ridges and grooves were numerous and compact. Desmosomes were more irregular in size, shape and distribution in cancerous cells than in BPH. Our observation indicated that the junctional complexes were altered and defective in cancerous cells and probably facilitated migration of some acinar cells into the stroma. In addition, we have also shown that the membranes including the intramembranous particles of Golgi complexes, mitochondria, secretory granules and vacuoles, lipofuscin granules and nuclei, were essentially similar in cancerous and BPH columar cells.

Freeze-fracture aspects of the junctional complexes in the round window membrane

Replicas of the freeze-fractured round window membrane were studied in chinchillas. Morphologically identifiable zonulae occludentes were found between the cells facing the tympanic cavity and between the cells bordering the perilymphatic space. Gap junctions were only found between the perilymphatic cells.

Glial cells in the earthworm ventral nerve cord make an A-type nexus

Nexuses have been demonstrated between glial cell processes in the earthworm ventral nerve cord. The nexuses have been demonstrated by freeze-cleavage to be A-type neuxuses, thus demonstrating for the first time the type of nexus present in the Annelida. If the nexal cleavage pattern has physiological significance then the results suggest that physiologically the nexuses of the earthworm may be similar to those of vertebrates.

In vivo and in vitro formation of the junctional complex in choroid epithelium. A freeze-etching study

The junctional complex of choroid epithelial cells was studied during in vivo formation, disaggregation after trypsin treatment, and in vitro reaggregation. The in vivo formation begins with the occurrence of amorphous patches of particles followed by the formation of small particulate rows and polygonal-ordered particle assemblies. Further arrangement of the zonula occludens continues with the confluence of particles and smooth contoured ridges. At the 9th day stage a fully developed zonula occludens has developed. In a subsequent step nexus become integrated within the tight junction formation. Disaggregation after trypsination results in fragmentation of the zonulae occludentes. Parts of the disassembling aggregates become incorporated in vacuoles indicating an endocytotic mode of "digestion". The in vitro reconstruction of the zonula occludens proceeds from remnants of the former zonula occludens. On the 3rd to 4th day of cultivation mature tight junctions are visible. In vitro integrations of nexus were observed during a later phase. On the 7th day, cultivated choroid epithelial cells reveal well differentiated junctional complexes consisting of continuous zonulae occludentes and integrated gap junctions.

Intercellular communication and tissue growth: IX. Junctional membrane structure of hybrids between communication-competent and communication-incompetent cells

The structure of the membrane junctions of the hybrid cell system, examined in the companion paper in respect to competence for communication through cell-to-cell membrane channels, is here examined by freeze-fracture electron microscopy. The junctions of the channel-competent parent cell and of the channel-competent hybrid cells present aggregates of intramembranous particles typical of "gap junction"; those of the channel-incompetent parent cell and channel-incompetent segregant hybrid cells do not. Competence for junctional communication and for gap junction formation are genetically related. The junctions of the intermediate hybrid cells with incomplete channel-competence (characterized by cell-to-cell transfer of small inorganic ions but not of fluorescein), present special intramembranous fibrillar structures instead of discrete gap-junctional particles. The possibility that these structures may constitute coupling elements with subnormal permeability is discussed in terms of incomplete dominance of the genetic determinants of gap junction.

Cell membrane structure of vascular smooth muscle of circle of Willis

Cell membranes of vascular smooth muscles of the circle of Willis were studied in thin sections and freeze-replicas. The cell membranes were differentiated into a caveolae intracellulares zone and caveolae-free zone, both of which were generally arranged in an alternate manner and parallel to the major axis of the smooth muscle cell. In the former zone, the caveolae intracellulares, about 600 A in diameter, were neatly oriented in one to several rows running parallel to the longitudinal axis of the muscle cell with a center-to center distance of about 800 A. The latter zone was of variable width and smooth, apart from membrane particles or scattered caveolae, and corresponded mainly to the dense area and partially to the myofibril area beneath the cell membrane. Membrane particles were generally more numerous on face A than on face B, and their average number per micronm2 was about twice as many inside the rows of the caveolae as outside. Rosette formations of membrane particles were often evident at the stomal rims of the caveolae. Adherentes and gap junctins were occasionally found on the caveolae-free areas which often protruded externally. Tight junctions appeared as a collection of scattered strands, which frequently showed free ends and were parallel to each other and also to the major axis of the smooth muscle cell.

Freeze-fracture studies of the developing cell surface. I. The plasmalemma of the corneal fibroblast

The freeze-fracture technique was used to study changes in the corneal fibroblast cell membrane during morphogenesis in chick embryos. Fibroblasts migrate into the acellular primary corneal stroma on day 6 of embryogenesis, moving between the orthogonal layers of collagen fibrils which serve as their substratum. Morphometric analysis of the intramembrane particles (IMP) reveals their concentration on the P face to decrease from 756 to 534/mum2 from day 6 to day 14. After day 14, fibroblast migration and cell division cease and the stroma condenses due to dehydration, so that by day 18 all of the layers of fibroblasts are extremely flattened and the cornea has taken on its mature, transparent form. The cell membranes of the terminally differentiated, highly compacted fibroblasts are rich in IMP (1,300/MUM2, P face). In seeking to relate the particle increase to cell differentiation, we analyzed synthetic events taking place at this time, but no correlation, we analyzed synthetic events taking place at this time, but no correlation with 25SO4 or proline-3H incorporation was found. The event which seems best correlated with the doubling of P face particles between days 15 and 18 is the dehydration and condensation of the stroma, an event which is associated with cessation of both cell division and migration. Thyroxine stimulates premature condensation of the stroma, whereas thiouracil delays condensation, but neither of these treatments affects IMP concentration. Interestingly, IMP concentration on the filopodia of migrating fibroblasts is similar to that on the cell bodies, suggesting that the new membrane has the same composition as the pre-existing membrane. Observations are also presented on tight and gap junctions between fibroblasts and on the relation of extracellular matrix to the outer etched surface of the fibroblast plasmalemma.

Gap junctions between the supporting cells in some acoustico-vestibular receptors

Extensive gap junctions are found between the supporting cells in acoustico-vestibular receptors (saccular macula of the goldfish; ampullar crista, utricular macula and organ of Corti of the guinea pig). The fine structural details of these gap junctions were examined using lanthanum hydroxide staining and freeze-fracture replicas, as well as conventional thin sections. It was found in the lanthanum treated saccular macula of the goldfish that the gap junction globules consist of five or six subunits surrounding a central 2 nm hole. Similar subunits of the gap junction globule are also found in freeze-fracture replicas of the saccular macula of the goldfish and the ampullar crista of the guinea pig. Possible functions of the extensive gap junctions between supporting cells of these receptors are discussed.

Freeze-fracture of the normal and pathological megakaryocyte lineage in chronic megakaryocytic-granulocytic myelosis

Freeze-fracture and thin sections were performed on human bone marrow of chronic megakaryocytic-granulocytic myelosis (CMGM) to study the three-dimensional fine structure and maturation of normal and atypical megakaryocytes and thrombocytes. In the many normally maturing megakaryocytes the development of the demarcation membrane system (DMS) was best investigated by comparison of thin sections with freeze-fracture replicas. The DMS shows no connections with the Golgi apparatus or rough-surfaced endoplasmic reticulum, but originates from tubular infoldings of the plasma membrane. These infoldings are always in continuity with the extracellular space and form an intracellular membranous pool by branching and coalescing of flattened tubules from which finally the perforated cisternae of the DMS arise. Freeze-fracture of the normal thrombocytes confirms earlier findings. The abnormal giant platelets seen in CMGM display extensive areas of smooth membranes of a spongy structure consisting of dense tubules surrounded by the labyrinth of the surface-connected system. Their physiological significance in these atypical platelets remains unsolved.

Intercellular communication and tissue growth: VII. A cancer cell strain with retarded formation of permeable membrane junction and reduced exchange of a 330-dalton molecule

A cancer (hepatoma) cell strain is described in which the formation of junctional membrane channels is abnormally slow. The development of electrical junctional coupling following the establishment of contact between these (reaggregated) cells is at least 15 times slower than that between their normal counterparts; and junctional transfer of fluorescein eventually develops, but only in about 5 per cent of the contacts (as against 100 per cent normally). This deviant membrane behavior is interpreted as a retardation in the process of accretion of junctional membrane channels. Its possible etiological role in defective growth regulation is discussed.

The distribution of intercellular gap junctions in the developing retina and pigment epithelium of Xenopus laevis

The distribution of gap junctions in the developing retina and pigment epithelium of Xenopus has been examined from optic vesicle to photoreceptor outer segment stages. In the retina and pigment epithelium walls of the optic vesicle gap junctions are found between ventricular cells in the apical contact zone and close to the outside wall; a neural tube type of distribution. Optic cup formation brings the retina and pigment epithelium into contact and gap junctions form between them. After the stage of retinal specification gap junctions, previously more numerous dorsally, are more often found in the ventral retina and pigment epithelium. They continue to be found in the retinal centre between ventricular cell processes in the apical contact zone and near the vitreal basement lamella above the ganglion cell layer until stage 35. Gap junctions are occasionally made by ganglion cells and their axons, providing possible pathways initiating cell differentiation. After stage 35 gap junctions seem to be confined to the peripheral rim of the eye cup where new cells are formed throughout larval life. The observed distribution suggests that gap junctions may provide intercytoplasmic pathways for retinal specification intrinsic to the retina and pigment epithelium.

Influence of the sodium pump on intercellular communication in heart fibres: effect of intracellular injection of sodium ion on electrical coupling

1. The effect of intracellular sodium injection on the electrical coupling between cardiac Purkinje cells was investigated. 2. It was found that an increase in the intracellular sodium concentration produces uncoupling in about 500 sec and increases the input resistance of the injected cell. Both effects were completely reversible. 3. Inhibition of the sodium pump by ouabain (6-8 x 10(7) M) also causes electrical uncoupling. 4. The decoupling of heart cells achieved by sodium injection was considerably accelerated in fibres treated with ouabain. 5. The influence of sodium injection on cell communication seems to be related to the intracellular calcium concentration 6. The above results indicate that the maintenance of a low intracellular sodium concentration by the sodium pump is essential for the preservation of a high junctional conductance in cardiac fibres.

Electrophysiological study of coupling between cultured cells of the mouse mammary gland in five distinct physiological states

Electrical coupling has been observed between cultured cells of the mouse mammary gland in five distinct physiological or pathological states. We have employed young primary cultures of cells dissociated from the following tissues: normal glands from young virgin or midpregnant females, hyperplastic alveolar nodules (believed to be precancerous) transplanted in gland-free mammary fat pads, and spontaneous mammary adenocarcinomas and their pulmonary metastases. All successfully impaled pairs of cells (a total of 97 pairs) were found to be ionically coupled. Furthermore, in normal and tumor cell cultures, electrical coupling was observed between dome-dome and dome-nondome cell pairs. This study correlates with electronmicroscopic studies of fresh normal, hyperplastic, and tumor samples, which show the presence of gap junctions in all three.

Tight and gap junctions in a vertebrate inner ear

The auditory organ of the alligator lizard has been investigated with the transmission electron microscope using methods which distinguish between tight and gap junctions. There is a continuous zone of tight junctions located near the endolymphatic surface of the organ forming a boundary between the endolymph in scala media and the interstitial spaces between the cells. No such tight junctions were observed between the perilymph of scala tympani and the interstitial fluid within the organ. Small gap junctions occur between hair cells and supporting cells and large gap junctions occur between adjacent supporting cells. The locations of the tight junctions suggest that the composition of the intercellular fluid in the receptor organ is probably more like perilymph than like endolymph. The presence of gap junctions between hair cells and supporting cells provides a possible morphological basis for the occurrence of intracellular responses to sound in supporting cells, and for elctric coupling of receptor cells.

Membrane structural specialization of the toad urinary bladder revealed by the freeze-fracture technique. II. The mitochondria-rich cell

Examination of the toad urinary bladder by freeze-fracture electron microscopy reveals that the mitochondria-rich cells of the epithelium possess distinctive and characteristic membrane structural specialization. Unique rod-shaped intramembrane particles are found in luminal and basal membranes as well as certain intracellular vesicles of this cell type. The consistent findings of two discrete patterns of luminal membrane structural organization supports the possibility that two morphological forms of mitochondria-rich cell exist within the toad bladder epithelium.