Length Of Junctions Research Articles

Gap junctions are non-randomly distributed inDrosophila wing discs.

The distribution of gap junctions in mature larvalDrosophila melanogaster wing discs was analyzed by means of quantitative electron microscopy. Gap junctions are non-randomly distributed in the proximal-distal disc axis and in the apical-basal cell axis of the epithelium. In the epithelial cells, the surface density, number and length of gap junctions are greatest in the apical cell region and distal disc region. The average gap junction surface density is 0.0572 μm-1 and 2.77% of the lateral cell surface is composed of gap junctions. In the adepithelial cells, the gap junction surface density is 0.0005 μm-1 and 0.06% of the cell surface is composed of gap junctions. No gap junctions were observed between epithelial cells and adepithelial cells. The absolute area of gap junctions was estimated in a proximal-distal strip of cells in the disc and is considerably less in the folded regions of the epithelium compared to the flat notum and wing pouch regions. The results are discussed with respect to pattern formation and growth control in imaginal discs.

Cellular junctions in perifollicular contractile tissue of the rat ovary during the preovulatory period.

Rat ovarian perifollicular contractile tissue was examined at specified intervals prior to ovulation to determine the type, relative number, and length of cellular junctions. Rat ovaries were taken for electron-microscopic observation at 1500 h on the afternoon of proestrus (proestrus 0-h group), at 2000 h (proestrus 5 h group), at 0100 h (proestrus 10-h group) and at 1600 h on the afternoon of diestrus I. Close junctions, intermediate junctions, and gap junctions were counted and measured. Then number of gap junctions/1,000 micrometers of membrane and the number of intermediate junctions/1,000 micrometers of membrane was significantly higher in the proestrus 10 h groups as compared to the other groups. There was no difference in the number of close junctions during the periods studied. Also the length of all junctions was similar in all groups. These morphological findings are discussed in the context of contractile role for perifollicular tissue in the ovulatory process.

Cell contacts in the kidney epithelium of Helisoma (mollusca: gastropoda)—Effects of osmotic pressure and brain extracts: A freeze-fracture study

Kidney epithelial cell contacts of Helisoma have been studied under different osmotic conditions (hyposmotic, isosmotic, control). In hyposmotic medium 20% of the observed zonulae adherentes appear opened, and septate junctions appear short with few septa or long with many septa showing irregular alignment and periodicity; intercellular spaces are wide. Snails from isosmotic medium show long septate junctions with compact regular septal periodicity and greatly reduced intercellular spaces. The length of septate junctions and the number of septa appear to be related to intercellular space width. Lanthanum-impregnated septa appear pleated and punctate. In freeze-fracture replicas septate junctions from hyposmotic medium have fewer rows or irregular sinuous rows of junctional particles. Osmotically induced changes in the junctional complexes are reversible. In vitro treatment with crude brain extract dramatically increases intercellular space width with significant changes in the junctional complexes. It is proposed that the septate junctions are involved in osmoregulation and a brain factor may regulate them. Gap junctions are found in various places in the kidney cell membranes; they may provide additional structural integrity in the epithelium. Rhombic particle arrays and desmosome-like particles have been observed in freeze-fracture replicas but their identity is unknown and no clear correlation for these particles in thin sections has been possible.

Ultrastructural changes with high activity and subsequent recovery at locust motor nerve terminals. A stereological analysis

The ultrastructural changes occurring at locust motor nerve terminals following a period of high activity and subsequent periods of rest have been stereologically evaluated from cross-sections. Retractor unguis muscles were fixed either immediately after stimulation of the motor nerve for 7 min at 20 Hz or after a subsequent rest of 2 min or 1 h and compared with unstimulated controls. In the regions of synaptic junctions there is, after stimulation, on average a decrease in the total number of synaptic vesicles of about 40% and a reduction of vesicle surface of about 20%; an increase in axolemma of 23%; an increase of about 70% in length of the profiles of smooth endoplasmic reticulum. After 2 min of rest these changes are largely reversed and with 1 h of rest no appreciable further changes are observed. The mean number of mitochondria is increased by about 40% immediately and 2 min after stimulation. The number and size of cisternae, the mean nerve terminal cross-sectional area and the length of the synaptic junctions do not change significantly under the different experimental conditions. The width of the synaptic cleft, however, is reduced by about 15% after stimulation, immediately and with 1 h of rest. In interjunctional regions the changes are similar but the axolemma shows no increase and the number of mitochondria declines by about 35% after stimulation. The calculated vesicle membrane per unit length of terminal lost after stimulation and the amount of axolemma gained are in the same range and the same applies to the corresponding gain of vesicular membrane and loss of axolemma after 2 min of rest. Depolarization of the terminals by elevated [K +] for 1 h has more pronounced effects of a similar kind, leading to considerable swelling and disorganization of mitochondria, an increase in the number of cisternae and swelling of the terminal. The results are consistent with an exo-endocytotic shift of membrane between vesicles and axolemma. The total membrane within the terminal is, however, somewhat reduced after stimulation. The transient increase in the amount of smooth endoplasmic reticulum could indicate a role in the formation of new vesicles for transmitter release or may be related to the sequestration of Ca 2+. Formation of cisternae is possibly relevant to degradation of membrane.

Hydrostatic pressure changes related to paracellular shunt ultrastructure in proximal tubule

We examined the effets of changes in hydrostatic pressures on the ultrastructural geometry of the lateral intercellular space and tight junctions in proximal tubules of contrtol (C) and volume-expanded (VE) Necturus kidney. The following groups of tubules were studied: (1) C, free-flow pressure, (2) C, stopped-flow, high-luminal pressure, (3) C, stopped-flow, low-luminal pressure, (4) VE, free-flow pressure, and (5) VE, stopped-flow, high-luminal pressure. Intratubular and peritubular capillary pressures were monitored before and during standardized perfusion-fixation for electron microscopy, and complete cross-sections of all sampled tubules were subjected to morphometric analysis. Average lateral intercellular space widths decreased significantly in C and VE stopped-flow tubules with high-luminal pressures but widened greatly in C stopped-flow tubules with low-luminal pressures. The length or width of the tight junctions did not change between the five experimental conditions. The ultrastructural changes correlate with the applied transepithelial pressure gradients rather than with transepithelial volume fluxes. The narrowing of lateral intercellular spaces in high pressure tubules correlate with the previously described increase in electrical resistance expressed per unit length tubule indicating that in these conditions part of the paracellular resistance is located in the free interspaces. The geometry of the lateral intercellular space in the proximal tubule of Necturus favors models of near-isotonic transport that do not depend on long and narrow interspaces.

Gap junctions in the myometrium of pelvic-neurectomized rats with blocked parturition.

AbstractPregnant Sprague‐Dawley rats were laparotomized on days 8–10 and sham‐operated (S) or subjected to bilateral section of the pelvic parasympathetic nerves (pelvic neurectomy (PN)). Both S and PN animals were allowed to go to term and the time of delivery was recorded. Eight of ten S animals delivered on the afternoon of day 22 and two delivered on the morning of day 23. Pelvic neurectomy blocked parturition in five rats autopsied on day 24, and five rats autopsied on day 26. On these days the PN animals had full‐term fetuses; live on day 24, but dead on day 26. In a second study, the fine structure of the myometrium of S and PN pregnant rats was examined during the parturient period for the presence of gap junctions. Gap junctions were present between myometrial smooth muscle cells of the S group during delivery and in the PN group on days 23, 24, and 25, in the absence of delivery. There was a significant increase (p < 0.05) in the number of gap junctions on day 23 in the PN animals. There was no difference in the length of gap junctions in the different groups. These observations indicate that the parturition block characteristic of PN animals is not attributable to the failure of gap junction formation between smooth muscle cells. Apparently, the nervi erigentes participate in the orchestration of events terminating in parturition, but their specific role remains an enigma.

Mechanisms of fluid absorption during proximal tubule development

Passive permeation characteristics and paracellular pathway ultrastructure were studied in vitro by perfusion of rabbit isolated proximal convoluted tubules during postnatal ontogenesis. The influence upon net volume flow (Jv) of transepithelial hydrostatic and protein osmotic pressure was significantly higher during early postnatal maturation than in the mature tubule. Hydraulic hydrostatic conductance (X10(-3) ml - cm-2 - min-1 - cm H2O-1) was 0.0367 +/- 0.0048 during early postnatal maturation (N = 99) and 0.0052 +/- 0.002 at maturity (N = 78). Hyperoncotic serum (12.7 +/- 0.4 g/100 ml) in the bath increased Jv by 67.5 +/- 21.1% from 0.31 +/- 0.06 to 0.52 +/- 0.08 nl-mm-1-min-1 in the neonatal proximal tubule, whereas an increase of only 25.7 +/- 20.4% from 1.08 +/- 0.15 to 1.32 +/- 0.18 nl-mm-1-min-1 was noted in the mature proximal tubule during this elevated bath protein-osmotic pressure. Electron microscopic observations showed that microperoxidase passed from tubule lumen through the basement membrane via intercellular spaces in immature tubules perfused at an increased transtubular pressure gradient. This suggests that a transepithelial shunt pathway may participate in changes of conductance during ontogenesis, although length and ultrastructural configuration of tight junctions did not vary with these variables. 1) Hydrostatic and oncotic water conductance of the rabbit proximal tubule changes with postnatal development. 2) Ultrastructural tracer studies suggest that the change in conductance is due to alteration of the paracellular pathway. 3) Isotonic absorption of the neonatal proximal tubule may depend more on transepithelial pressure gradients than in the mature tubule.

Retinal capillary junctions: ultrastructural tight junction artefacts induced by sodium ions and membrane reduction in streptozotocin diabetes.

Retinal capillary junctions were analysed in normal and diabetic rats and in a human retina with the electron microscope. Diabetes mellitus was induced with streptozotocin. The retinae were fixed in Palade's osmium tetroxide containing sodium or calcium ions and block-stained in uranyl acetate. With Ca-fixation, no significant difference in interendothelial cleft width was detected between retinal layers or between normal and diabetic retinae. Diabetes caused a narrowing of the clefts in the Na-fixed tissue X +/- SE, n=375; Normal: 78.6 +/- 300 A; Diabetic: 57.7 +/- 2.42 A; p less than 0.001). A significant correlation was found between cleft width and the length of the tight junctions or zonulae occludentes (p less than 0.001). In the nerve fibre layer of the Na-diabetic retina, where cleft narrowing was greatest, there was an increase in length of the zonulae occludentes from 22.8 +/- 2.2% to 41.6 +/- 3.7% (p less than 0.001). Ca-fixation prevented these changes, indicating that at least some zonulae occludentes were interendothelial extraction artefacts. In the normal retina, endothelial cell membrane thickness was greater with Ca- than Na-fixation (p less than 0.001). Diabetes caused a decrease in membrane thickness of Ca-fixed tissue (p less than 0.001). The diabetic decrease in membrane thickness may explain the increased fragility and increased permeability of diabetic capillaries. Calcium binding by endothelial cell membranes is of primary importance in anticoagulation which is defective in diabetes.