Lanthanum "staining* of the lateral and basal membranes of the mitochondria-rich cell in toad bladder epithelium

The events relating to lanthanide ions enhanced permeability of human erythrocyte membrane: binding, conformational change, phase transition, perforation and ion transport

The binding and uptake of Gd3+ ions by human erythrocytes in vitro were studied by determining the Gd contents in membrane and in cytosol by means of particle-induced X-ray emission (PIXE) spectrometry. Results obtained from varied incubation time revealed that the Gd3+ ions bind to the membrane proteins and lipids at first. Gd3+ binding to the membrane lipids and proteins lasts 0 approximately 20 and 20 approximately 100 ms respectively, as shown by the stopped-flow studies. Then a fraction of Gd3+ ions diffuses through the membrane. The kinetics of Gd3+ binding indicates that the binding to phospholipids is prior to that to the membrane proteins, but a portion of the lipid-bound Gd3+ redistributed later to the proteins. PIXE studies showed that the entry of Gd3+ increased the influx of Ca2+ and Cl-. By monitoring the changes in fluorescence of proteins and that of the Ln3+, the uptake of La3+, Eu3+, Gd3+ and Tb3+ was shown to be a process comprising a series of events. Binding to the membrane molecules induces the phase transition of lipid bilayer and conformational changes and aggregation of membrane proteins. Conformational changes of the proteins were characterized by Fourier transform IR spectroscopy (FT-IR) deconvolved spectra, i.e. alpha-helix content decreases while beta-sheet increases. ESR spectra of MSL-labeled proteins reflect the aggregation state related with the conformational change. [31P]NMR spectra of membrane lipid bilayer revealed the Ln3+ ions induced hexagonal (H(II)) phase formation. Phase transition and aggregation of membrane proteins cause the formation of domain structure and perforation in the membrane. These alterations in membrane structure are responsible for the Ln3+ enhanced membrane permeability. Thus the previous Ln3+ binding will facilitate the across-membrane transport of other Ln3+ ions through the membrane.

Diffusion barrier properties of the perineurium: an in vivo ionic lanthanum tracer study

While the perineurium as a diffusion barrier has been extensively investigated by light and electron microscopy, such studies have been largely restricted to the use of protein tracers. In the present study the permeability of the perineurium to a physiologically more relevant ionic tracer has been assessed. In vivo the rat sural or tibial nerve was either microinjected with lanthanum nitrate solution for endoneurial application or bathed in the lanthanum solution for epineurial application. The findings generally demonstrated an effective barrier to the tracer which failed to penetrate the inner layers of the perineurium. Only at the highest lanthanum concentration and longest time intervals employed did trace quantities occasionally penetrate the barrier and then only in the presence of some cytopathological changes to the outermost perineurial cells. The usefulness of the microinjection method was limited by the slight but unavoidable trauma to the perineurium. The findings are related to those of other studies which have used electron dense tracers, also to studies using physiological including electrophysiological techniques and morphological including freeze-fracture methods.

Ultracytochemical localization of calcium in the superficial pineal gland of the Mongolian gerbil

In order to demonstrate fine localization of Ca2+ in the superficial pineal gland of Meriones unguiculatus, the pyroantimonate technique was employed. Control experiments were performed with EGTA and analysis of obtained reaction product using an energy-dispersive x-ray microanalysis. Precipitates of calcium antimonate were formed almost exclusively in swollen clear pinealocytes, in and along their cell membranes, over their nuclei, in mitochondria, the Golgi apparatus, endoplasmic and integrade reticulums, acervuli, in vesicles surrounding synaptic bars, cytoplasmic matrix, and flocculent extracellular material. It has been concluded that the swollen pinealocytes represent a degenerative cell form probably occurring by impairment of plasmalemmal Ca2+-ATPase's ability to eliminate Ca2+ ion from the cell, with consecutive increase of calcium in the cytoplasmic matrix, followed by increase of intramitochondrial Ca2+ concentration, gradual arrest of mitochondrial function, depolymerization of cytoskeletal microtubuli, loss of the cell form, and cell death. Decrease of function of pinealocyte plasmalemma seems to be related to aging.

Nodes of Ranvier and Schmidt-Lanterman incisures: an in vivo lanthanum tracer study

The permeability of the tight junctional system of myelin, at the juxtanodal myelin terminal loops and Schmidt-Lanterman incisures, was investigated using the ionic tracer lanthanum (a) in vivo followed by fixation, (b) concurrently with fixation, (c) following fixation. Employing the same methods the juxtanodal membrane complex formed between myelin loops and axolemma was also tested. The results of this study demonstrate that the periaxonal space (between axon and Schwann cell) is apparently accessible to lanthanum via the myelin loop-axolemmal junction, irrespective of the mode of exposure of myelinated fibres to the tracer. Similarly, the tight junctions between adjacent myelin terminal loops apparently do not prevent lanthanum penetration either in living or in fixed nerves. By contrast the tracer obtained access to the extracellular space within incisures only in vivo. The results are interpreted in terms of the permeability of nodes and incisures in vivo to physiologically important ions and related to current concepts of the electrophysiology of the myelinated nerve fibre.

The use of lanthanum chloride as a marker for intercellular junctions in rat exocrine pancreas

A simple technique of perfusion and immersion of tissue in fixative containing lanthanum chloride as an extracellular tracer is described. In addition to functioning as a tracer, the lanthanum chloride appears to enhance electron staining. In rat exocrine pancreas, intercellular spaces between exocrine and centroductular cells were outlined clearly be electron dense material and, at cellular interfaces, spot desmosomes, gap junctions, and tight junctions were demonstrated. The technique proved simple and effective and should prove useful in studies of epithelial and other tissues.

Lanthanum as an intracellular stain for electron microscopy

Results obtained after the normal aldehyde fixation of duodenal enterocytes for electron microscopy have been compared with results obtained when 0.1% Malachite Green or 10 mM lanthanum chloride had been added during aldehyde fixation. Sections were examined without further staining, and after counterstaining with lead citrate and uranyl acetate. In unstained sections, lanthanum-treated material showed improved contrast when compared to results from the other two methods. Also, after counterstaining, areas showing excellent contrast were much more frequent and more readily detected in the lanthanum-treated material. In the microvilli of enterocytes fixed in the presence of lanthanum, the plasmalemma-glycocalyx was defined more clearly and the results were more pleasing subjectively. When Malachite Green was present in the fixative, good contrast was observed more frequently than in routinely fixed tissues, but less often than in those treated with lanthanum. It is suggested that the addition of lanthanum chloride or Malachite Green to the fixative may prove useful in many ultrastructural studies.

Effect of hydrostatic pressure on ADH induced osmotic water flow in toad bladder

The effect of hydrostatic pressure (HP) on antidiuretic hormone (ADH) stimulated osmotic water flow (Jv) across the toad urinary bladder was evaluated. Jv for ADH-stimulated bladders was significantly reduced by an elevation of the serosal HP gradient to 1 cm H2O. Subsequent elimination of the HP gradient resulted in a recovery of Jv. Serosal HP also caused a reversible increase in sucrose permeability (P sucrose). For ADH-treated bladders fixed with glutaraldehyde during serosal HP exposure, subsequent exposure to a mucosal or serosal HP gradient caused acceleration or inhibition of Jv, respectively. The reduction in ADH-associated Jv with serosal HP was apparently caused by a back-flux of water through a paracellular pathway. Jv and P sucrose were not affected by mucosal HP during ADH stimulation. The results suggest a specific sensitivity of a paracellular pathway to a small serosal HP gradient in bladders with ADH-stimulated water flow. The reversibility of this effect on P sucrose suggests that the elements comprising the apical junctions are dynamic structures capable of recovering at least some of their permeability properties.

Mitochondrial calcium of intact and mechanically damaged bone and cartilage cells studied with K-pyroantimonate

Cellular cation was localized with K-pyroantimonate osmium fixation in whole fetal mouse metatarsal bones and in deliberately mechanically damaged specimens. X-ray microprobe analysis of ultrathin sections showed a positive correlation between the concentration of Ca (and Sb) and the amount of electron-dense precipitate. In non-damaged osteoblasts and growth-plate chondrocytes dense precipitate had accumulated along the plasmalemma and the mitochondrial membranes, whereas damaged cells showed the precipitate on round granules in the mitochondrial matrix but not on membranes. Intermediate stages between these two patterns were also found. In a non-calcifying tissue such as liver no membrane-bound precipitate was found in intact cells. However, damaged liver cells showed precipitate-containing mitochondrial granules similar to those in damaged bone cells, but only after incubation of the damaged tissue for 1 h in a Ca-containing balanced salt solution. Freezing of fresh whole bones in liquid N2 before fixation in K-pyroantimonate osmium did not change the precipitate pattern in the damaged cells, but in intact cells it produced a random distribution of precipitate unrelated to membranes. The results are compared with those obtained in other studies on the subcellular localization of calcium and in biochemical studies on membrane versus matrix loading in calcium-accumulating isolated mitochondria.

Effects of mucosal lanthanum on electrical parameters of isolated frog skin. Mechanism of action

The effect of mucosal La3+ on electrical parameters of isolated frog skins was studied on isolated frog skins with normally polarized or depolarized apical membrane. La3+ increases R8, the paracellular or shunt resistance and diminishes RNa, the resistance of the active sodium path, in both polarized and depolarized skins. The stimulatory effect of La3+ on short-circuit current (Is.c.) is correlated with this decrease in RNa. The characteristics of the stimulatory effect are: very rapid onset, ionic strength dependency, the possibility of being elicited by many other ions besides La3+. These features allow us to postulate that La3+ might affect the external interfacial potential which in turn affects the resistance of the sodium path.