The morphology of the toad urinary bladder: A stereoscopic and transmission electron microscopical study

Summary The appearance of the mucosal cell layer of the isolated urinary bladder of the toadBufo marinus, has been examined using stereoscopic and conventional transmission electron microscopy.Three cell types can be identified in surface view, these are granular cells, mitochondriarich cells and goblet cells. Cell boundaries between granular cells are clearly defined by membranous folds along their margins. Although no changes are seen in the stereoscopic electron micrographs when the granular cells are made permeable to water by vasopressin, the changes observed on transmission electron micrographs include swelling of cell bodies and nuclei, filling of intercellular channels with water, and the appearance beneath the mucosal cell membrane surface of electron dense granules.Differences between the appearance of the bladder mucosal cells by the two methods of electron microscopical examination are due largely to water loss when the tissue is freeze dried prior to stereoscopic examination.Grateful thanks are due to Dr. W. D. E. Thomas and Miss Elizabeth Hull of the Long Ashton Research Station for use of the Stereoscan microscope, and also to Dr. John Clamp and Mr. P. J. Summers for help and advice.In receipt of a personal research grant from the Medical Research Council, London.     

Effects of colchicine and cytochalasin B on hypertonicity-induced changes in toad urinary bladder

Summary Coincident with an increase in the water permeability of toad urinary bladder induced by serosal hypertonicity, a transformation of the ridge-like surface structures of the granular cells into individual microvillous structures occurs. This study was initiated to establish whether the transformation is mediated by the cytoskeletal network and, thus, can be prevented by disruption of microtubulemicrofilament function with colchicine or cytochalasin B (CB). Scanning electron microscopy revealed the characteristic branching ridges on granular cells of control bladder incubated with colchicine or CB. In contrast, transformation of ridges to discrete microvilli was observed in experimental bladders exposed to serosal hypertonicity alone or in combination with either colchicine or CB. These results suggest that the mechanism underlying hypertonicity-induced surface changes which are associated with increased water permeability does not involve either microtubules or microfilaments.     

Mucosal surface morphology of the toad urinary bladder. Scanning electron microscope study of the natriferic and hydro-osmotic response to vasopressin

The mucosal cell surface of the toad urinary bladder was examined by scanning electron microscopy, and changes in the structure of the surface of the granular cell were correlated with specific physiological responses to vasopressin. Survey views of the mucosal surface demonstrated that there was no consistent repeating anatomical relationship between the granular cell and the mitochondria-rich cell that would support the concept of cooperativeness in the response to vasopressin. During base-line states of Na+-transport and water flux, the microvilli on the mucosal surface of the granular cell are arranged in a ridge-like network with occasional individual projections. When water flux is increased by exposing the tissue to vasopressin, in the presence of an osmotic gradient across the tissue the microvilli on the granular cell lose the ridge structure and appear, predominantly, as individual projection. Variability-of this appearance points out the necessity of examining large areas and many samples before the significance of any morphological change can be assessed. Blocking the simultaneously occurring natriferic response of the toad urinary bladder with 10(-2)M ouabain does not prevent these changes in the microvilli. When the hydro-osmotic response is blocked by eliminating the osmotic gradient, the granular cell shows no consistent change in mucosal surface morphology even when fixed at the height of the natriferic response. The mitochondria-rich and mucous cells did not show any change in morphology throughout these studies. We conclude that the changes in the mucosal surface morphology of the toad bladder seen after exposure to vasopressin are a result of the increased water flux that occurs when an osmotic gradient exists across the tissue, and are not related to the natriferic response or any specific alteration in the membrane properties.     

The morphology of the esophageal mucosa of the rat: a scanning electron microscopic study

The morphology of the oesophageal mucosa of adult male and female albino rats (Rattus norvegicus) is studied by means of scanning electron microscopy of several levels. A precise surface analysis of the upper, middle, and lower portion of the esophagus is done and the results are compared with each other.     

Three-dimensional scanning electron microscopic study of the normal hamster olfactory epithelium

Brain Cell Biology - The olfactory epithelium of the adult hamster (Mesocricetus auratus) was studied using the scanning electron microscope. A method that produced fractures in the epithelium...     

Effects of melittin on a model renal epithelium, the toad urinary bladder

The bee venom melittin, 10(-6) M, on the mucosal (urinary) side of the toad urinary bladder (in vitro), markedly decreased transepithelial potential difference, short-circuit current (Isc, sodium-dependent) and resistance. However, these effects were not seen when the toxin was placed on the opposite (serosal) side of the membrane preparation. The electrical effects were accompanied by a large increase in the transepithelial permeability to 22Na. The response was not changed by meclofenamic acid (which blocks formation of prostaglandins) but it was inhibited by La3+. In the presence of amiloride, which usually inhibits active Na transport and Isc, melittin, on the mucosal side, increased the Isc. The action of melittin appears to involve an interaction with anionic sites, which mediate its effects. Such sites appear to be present on the apical plasma membranes of the toad bladder epithelial cells, but they are not as abundant or they are inaccessible on the basal plasma membrane.     

Transport-related modulation of the membrane properties of toad urinary bladder epithelium.

Impedance analysis and transepithelial electrical measurements were used to assess the effects of the apical membrane Na+ channel blocker amiloride and anion replacement on the apical and basolateral membrane conductances and areas of the toad urinary bladder (Bufo marinus). Mucosal amiloride addition decreased both apical and basolateral membrane conductances (Ga and Gbl, respectively) with no change in membrane capacitances (Ca and Cbl). Consequently, the specific conductances of these membranes decreased without significant changes in membrane area. Following amiloride removal, an increase was obtained in the steady-state rate of sodium transport compared to values before amiloride addition. This increase was independent of the initial transport rate, suggesting activation of a quiescent pool of apical sodium channels. Chloride replacement by acetate or gluconate had no significant effects on apical or basolateral membrane capacitances. The effects of these replacements on membrane conductances depended on the anion species. Gluconate (which induces cell shrinkage) decreased both membrane conductances. In contrast, acetate (which induces cell swelling) increased Ga and had no effect on Gbl. The increase in the apical membrane conductance was due to an increase in the amiloride-sensitive Na+ conductance of this membrane. In summary, mucosal amiloride addition or chloride replacements led to changes in membrane conductances without significant effects on net membrane areas.     

Differential effects of aldosterone and ADH on intracellular electrolytes in the toad urinary bladder epithelium

Summary Quantitative electron microprobe analysis was employed to compare the effects of aldosterone and ADH on the intracellular electrolyte concentrations in the toad urinary bladder epithelium. The measurements were performed on thin freeze-dried cryosections utilizing energy dispersive x-ray microanalysis. After aldosterone, a statistically significant increase in the intracellular Na concentration was detectable in 8 out of 9 experiments. The mean Na concentration of granular cells increased from 8.9±1.3 to 13.2±2.2 mmol/kg wet wt. A significantly larger Na increase was observed after an equivalent stimulation of transepithelial Na transport by ADH. On average, the Na concentration in granular cells increased from 12.0±2.3 to 31.4±9.3 mmol/kg wet wt (5 experiments). We conclude from these results that aldosterone, in addition to its stimulatory effect on the apical Na influx, also exerts a stimulatory effect on the Na pump. Based on a significant reduction in the Cl concentration of granular cells, we discuss the possibility that the stimulation of the pump is mediated by an aldosterone-induced alkalinization.Similar though less pronounced concentration changes were observed in basal cells, suggesting that this cell type also participates in transepithelial Na transport. Measurements in mitochondria-rich cells provided no consistent results.     

Investigation of articular cartilage surface morphology with a semiquantitative scanning electron microscopic method

A semiquantitative scanning electron microscopic method for analysis of the articular cartilage surface morphology was developed. The method was based on a survey of large picture montages (ca. 70 X 100 cm) and classification of the cartilage surface changes at three levels. Computer technique was utilized in the analysis. The method ensured numerical expression and statistical treatment of the results. With this method we investigated the effects of physical exercise and immobilization on the articular cartilage of rabbit patella.     

The ependymal surface of the fourth ventricle of the rat: a combined scanning and transmission electron microscopic study.

The morphological features of the ependymal surface and supraependymal elements of the fourth ventricle of the rat were examined by scanning electron microscopy (SEM) and by the transmission electron microscopy (TEM). The results confirm the following aspects: 1) The presence of supraependymal elements and microvilli in the ependymal territories, including the sites where the cilia completely cover the ependymal surface; 2) The existence of cilia with oval or spherical thickenings together with supraependymal bulbs similar in size to those of the larger ciliary swellings; 3) Identification of the long supraependymal fibres with intermittent fusiform dilations observed under the SEM with the nerve fibres seen under the TEM; 4) The existence of intraventricular axodendritic synapses.     

Filamentous microbes indigenous to the murine small bowel: A scanning electron microscopic study of their morphology and attachment to the epithelium

Segmented, filamentous prokaryotic microorganisms colonize and attach to the cells in the epithelium of the mucosa of the small bowels of mice and rats. Scanning electron micrographs, derived from specimens of mouse small intestine, reveal microbial filaments of at least two types. One type is thin (0.8m) with only faint lines suggesting septa; the other is thicker (1.4m) and has distinct segments with pronounced septa. Most of the segments are rounded; a few are thin and elongated. Immediately surrounding the attachment site of these organisms, the surface of the epithelial cells appears roughened and occasionally stringy. The filaments may differ morphologically because they represent different phases in the life cycle of a single microbial type. Alternatively, however, they may differ because they are the cells of different microbial types colonizing the same epithelial habitat.     

The vasculature of the rat penis: a scanning electron microscopic and histologic study.

As a basis for understanding the mechanism of erection in an animal model frequently used in research in reproductive biology, the angioarchitecture of the penis of the rat has been described using scanning electron microscopy. Study of the penile vasculature of the rat indicates that the corpora cavernosa penis and the corpus spongiosum are independent erectile tissues, each with its own arterial and venous vessels. The large vascular spaces and abundant smooth muscle of the penile crura are compatible with its role in regulating blood flow to more distal penile tissues. Helicine arteries of the crura, but not the parent deep penile artery or arteries elsewhere, have muscular cushions in their walls. The venous drainage of the penile crura is via subtunical veins which are thought to be compressed during erection to elevate pressure within the penis. Large, paired cavernous veins drain the shaft of the penis. A unique method for inhibiting blood flow from the penis is indicated by the division of the cavernous veins into smaller channels prior to joining the subtunical venous plexus. Erectile tissue in the bifid origins of the corpus spongiosum has abundant cavernous muscle, while in the remainder of the corpus spongiosum little smooth muscle lines the cavernous spaces. The cavernous spaces on either side of the urethra coalesce to form vessels, each of which communicates with cavernous spaces in the glans. In addition, a bypass of the glans is effected by communication of these vessels directly with the deep dorsal vein. The apparent absence of muscular pads in vessels of the spongiosum, the relative paucity of cavernous smooth muscle, and the ample venous drainage provided by the deep dorsal vein may account for the lack of a venous occlusive mechanism similar to that of the corpora cavernosa penis.     

Microelectrode studies in toad urinary bladder epithelium. effects of Na concentration changes in the mucosal solution on equivalent electromotive forces

Microelectrode techniques were employed to measure membrane potentials, the electrical resistance of the cell membranes, and the shunt pathway, and to compute the equivalent electromotive forces (EMF) at both cell borders in toad urinary bladder epithelium before and after reductions in mucosal sodium concentration. Basal electrical parameters were not significantly different from those obtained with impalements from the serosal side, indicating that mucosal impalements do not produce significant leaks in the apical membrane. A decrease in mucosal Na concentration caused the cellular resistance to increase and both apical and basolateral EMF to depolarize. When Na was reduced from 112 to 2.4 mM in bladders with spontaneously different baseline values of transepithelial potential difference (Vms), a direct relationship was found between the change in Vms brought about by the Na reduction and the base-line Vms before the change. A direct relationship was also found by plotting the change in EMF at the apical or basolateral border caused by a mucosal Na reduction with the corresponding base-line EMF before the change. These results indicate that resting apical membrane EMF (and, therefore, resting apical membrane potential) is determined by the Na selectivity of the apical membrane, whereas basolateral EMF is at least in part the result of rheogenic Na transport. These results are consistent with data of others that suggested a link between the activity of the basolateral Na pump and apical Na conductance.     

A scanning electron microscopic study of the dorsal surface of the human tongue

To study the dorsal surface of the human tongue using a scanning electron microscopy (SEM), tissue specimens were taken from the anterior part of the tongues of 15 individuals aged from 21- to 28-years-old. The formalin-fixed samples were processed routinely for SEM. With SEM the surface of the normal tongue mucosa was shown to be rather evenly covered by filiform papillae, with some fungiform papillae scattered among them. Filiform papillae consisted of two parts: the body and hairs. The mucosal surface of the body was smooth; the squamous epithelial cells were polygonal, and their boundaries were prominent. On the surface of the superficial epithelial cells were parallel or branching microplicae. Each filiform papilla had 6-10 hairs, which were scaled and covered by an extensive plaque of microorganism. The upper surface of the fungiform papillae was smooth; only a few desquamating cells were seen. The superficial cells had a pitted appearance and cell boundaries overlapped. Taste pores, up to 3 pores in a single papilla, were found on the upper surface. Desquamation was more pronounced on the base of the fungiform papillae than on the upper surface. In almost all fungiform papillae some hairs protruded from the base. Parallel microplicae were found on the surface of the superficial cells of the base. The structure and function of the human tongue, as well as the microplicae of its superficial cells, are compared to those of various species of animals.     

Sodium transport effects on the basolateral membrane in toad urinary bladder

In toad urinary bladder epithelium, inhibition of Na transport with amiloride causes a decrease in the apical (Vmc) and basolateral (Vcs) membrane potentials. In addition to increasing apical membrane resistance (Ra), amiloride also causes an increase in basolateral membrane resistance (Rb), with a time course such that Ra/Rb does not change for 1-2 min. At longer times after amiloride (3-4 min), Ra/Rb rises from its control values to its amiloride steady state values through a secondary decrease in Rb. Analysis of an equivalent electrical circuit of the epithelium shows that the depolarization of Vcs is due to a decrease in basolateral electromotive force (Vb). To see of the changes in Vcs and Rb are correlated with a decrease in Na transport, external current (Ie) was used to clamp Vmc to zero, and the effects of amiloride on the portion of Ie that takes the transcellular pathway were determined. In these studies, Vcs also depolarized, which suggests that the decrease in Vb was due to a decrease in the current output of a rheogenic Na pump. Thus, the basolateral membrane does not behave like an ohmic resistor. In contrast, when transport is inhibited during basolateral membrane voltage clamping, the apical membrane voltage changes are those predicted for a simple, passive (i.e., ohmic) element.     

The surface of the conjunctiva in domestic ruminants. A scanning electron microscopic investigation

The surface of the conjunctiva was investigated in goats, sheep and bovines. The lid-facing surface of the nictitating membrane carries a serrated crest. At a low magnification the areas covered by a stratified squamous epithelium appear as a mosaic. In the superior and inferior conjunctival fornices the mucous membrane has a uniform appearance. Areas of goblet cells have an irregular appearance. Four functional stages can be observed in the goblet cells. At a high magnification the superficial cells of the palpebral and bulbar conjunctiva are covered by microplicae. In the fornix conjunctival microvilli project over the superficial cells.