Transcellular Passage Research Articles

Transcellular labeling of taste bud cells by carbocyanine dye (diI) applied to peripheral nerves in the barbels of the catfish, Ictalurus punctatus

In order to study the pattern of innervation of taste buds and the surrounding epithelium, the carbocyanine dye diI was applied to the nerve stump in isolated, paraformaldehyde-fixed barbels obtained from channel catfish, Ictalurus punctatus. After a diffusion period of 7-41 days, the barbels were sectioned on a vibratome and examined with epifluorescence. Labeled axons were observed up to 1 cm from the site of application. Frequently, a fascicle of labeled axons turned outward toward the epithelium to innervate taste buds or to end apparently as free endings within the epithelium. Within 2-3 mm of the dye-application site, many taste buds contained one or at most 5-10, labeled spindle-shaped, presumed receptor, cells. In taste buds containing multiple labeled cells, the cells usually were arranged as intertwined pairs or triplets rather than being homogeneously distributed within the taste bud. In a few cases, labeled basal cells could be discerned among the labeled axons of the basal plexus. The cells of the taste bud apparently were labeled by transcellular passage of the dye from the nerve fibers into the cells. The limited number of labeled cells within each taste bud may indicate a special relationship between these cells and the nerve fibers innervating them.

Tauroursodeoxycholate prevents taurolithocholate-induced cholestasis and toxicity in rat liver

Ursodeoxycholate has been advocated for the treatment of cholestatic liver diseases. The coinfusion of tauroursodeoxycholate with taurolithocholate in the perfused rat liver completely prevented the decrease of bile flow and the increase of oxygen uptake found with taurolithocholate only. Bile flow and bile salt secretion were increased with the coinfusion of both bile acids as compared with the infusion of tauroursodeoxycholate only (+4.30 microliters/g liver per 30 min) with 16 and 32 mumol/l tauroursodeoxycholate (+1.55 microliters/g liver per 30 min with 80 and 160 mumol/l). Morphological examination revealed a 50% decrease of the number of necrotic cells in the periportal area. Tauroursodeoxycholate did not inhibit the uptake of taurolithocholate, but increased its transcellular passage and biotransformation. Thus, tauroursodeoxycholate prevents taurolithocholate-induced cholestasis and liver cell toxicity probably by an intracellular mechanism.

Ovarian structural specializations facilitate aplacental matrotrophy in Jenynsia lineata (cyprinodontiformes, osteichthyes).

Jenynsia lineata retains its embryos within the ovarian cavity for a prolonged gestation. In the absence of egg envelopes, maternal-embryonic transfer occurs through ovarian fluid across apposed epithelia, relatively lining the ovarian lumen and the surface of the embryos. There are no hypertrophied extraembryonic structures that could provide expanded exchange surfaces for the passage of nutrients beyond the 8-mm stage, but structural specializations of the ovary then form, and these may sustain embryogenesis. Outgrowths of the inner lining of the ovary, villi ovariales, enter the pharyngeal cavity of the embryos via an opercular cleft remaining from early stages of development, after depletion of yolk reserves, until shortly before term. The ovary and its villi are lined by a monolayer of squamous cells showing evidence of vesicular transport of macromolecular substances both on the apical surface and at the basolateral pole. It serves for transcellular passage of maternally derived substances rather than as a source of secretory products. Most adjacent cells interdigitate, and the epithelium is continuous except for few gaps at the villous tips, which allow paracellular passage of particulate matter. These epithelial cells contain abundant filaments, electron-dense granules within the cytoplasm and the nucleus, sparse elements of the rough endoplasmic reticulum, a Golgi apparatus, and different sorts of vacuoles. The capillaries in the intraovarian lining are spaced most densely at the ovarian wall, less so toward the tips of the villi. The villi ovariales contain a network of connective tissue that forms endotheliumlike septa, which divide the interior into numerous different-sized loculi.

Maternal-embryonic relationships in the goodeid teleost, Xenoophorus captivus

The endodermal trophotaenial epithelium in goodeid embryos acts as a placental exchange site. Fine structural and cytochemical data indicate that the trophotaenial absorptive cells are endocytotically highly active. To test their micropinocytotic capacity and characterize the cellular mechanisms involved in membrane, solute and ligand movements, living embryos of Xenoophorus captivus were incubated in saline media containing horseradish peroxidase (HRP) and/or cationized ferritin (CF) in vitro, and the uptake of these tracer proteins examined by both time sequence analysis and pulse-chase procedures. In some embryos, the effects of prolonged exposure to CF injected into the ovarian cavity, was also investigated. Labelling of the free cell surface was detectable with CF only, but interiorization of both probes was quick from all incubation media. Adsorptive pinocytosis of CF and fluid-phase uptake of HRP sequentially labelled pinocytic vesicles, endosomes, and lysosome-like bodies. In addition, CF-molecules were sequestered within apical tubules and small vesicles. HRP was largely excluded from both organelles and ended up in the lysosomal compartment. For CF, two alternative pathways were indicated by the pulse-chase experiments; transcellular passage and regurgitation of tracer molecules to the apical cell surface. The latter procedure involves membrane and receptor recycling, in which apical tubules are thought to mediate. In double-tracer experiments, using an 8:1 excess of HRP, external labelling with CF was light or lacking after 1-3 min, and the initial uptake-phase produced pinocytic vesicles and endosomes that mainly contained HRP-reaction product. Prolonged incubation, however, resulted in densely CF-labelled plasmalemmal invaginations and pinocytic vesicles that predominantly carried ferritin granules. After 60 min, the vacuoles of the endosomal compartment contained either high concentrations of HRP-reaction product, both tracers side by side, or virtually exclusively CF.

Gastrointestinal Absorption of Intact Proteins

There is now no reasonable doubt that small quantities of intact proteins do cross the gastrointestinal tract in animals and adult humans, and that this is a physiologically normal process required for antigen sampling by subepithelial immune tissue in the gut. It is too small to be nutritionally significant in terms of gross acquisition of amino-nitrogen, but since it has important implications relating to dietary composition it must receive consideration from nutritionists. The process of intact protein absorption occurs without eliciting harmful consequences for most individuals, but it appears likely that a small number of people absorbing these "normal" amounts may react idiosyncratically; also, some individuals may absorb excessive amounts, and they may suffer clinically significant consequences. Likewise, individuals with diminished absorption of intact protein may be at risk. Normal absorption probably occurs predominantly by transcellular endocytosis with some possible contribution by a route between cells; increased net entry of protein to the circulation may reflect (a) increased paracellular (intercellular) passage, (b) increased transcellular passage, and/or (c) decreased lysosomal proteolysis. Tests to distinguish among these possibilities are strongly desirable. Intact protein absorption may be involved in the pathogenesis of inflammatory bowel disease, "food allergies," and other diseases, including even major psychiatric disorders, but the current evidence is mainly indirect and suggestive. Great caution and careful objective studies are needed to establish whether such relationships with disease do exist and to unravel the underlying basic physiological mechanisms. Now that interest has developed in the assessment of intestinal permeability to small- and medium-sized molecules, it is hoped that equally simple methods for studying macromolecular permeability will be developed and applied. Therapeutic methods for enhancing intact polypeptide absorption would be valuable for vaccine and peptide drug administration by the oral route. Therapeutic reduction of the process may be relevant in food-sensitive patients.

Growth and metastasis of Lewis lung carcinoma in the footpad of mice.

When Lewis lung carcinoma cells were transplanted into the footpad of mice, exponential growth of tumour was seen from the 4th day. Intravasation of tumour cells was first seen at this time, then increased steadily up to the 10th day. Tumour cells entered the circulation by destructive degeneration of the vascular endothelium and also by transcellular passage, mainly through capillaries, venules and thin-walled tumour vascular channels. Multiple sites of entry of tumour cells into the circulation were frequently found. The rate of intravasation of tumour cells into the circulation was the same at the proximal, middle and distal portions of the tumour.

Genetic hypothesis of idiopathic schizophrenia: its exorphin connection.

This brief overview proposes a testable oligogenic model of the inheritance of susceptibility to idiopathic schizophrenia: "abnormal" genes at each of a few complementary loci. The model is based on my assumptions as to the likely genetic abnormalities at possibly four or five interacting loci that would permit exorphins, the opioid peptides from some food proteins, especially glutens and possibly caseins, to go from gut to brain and cause symptoms of schizophrenia. Exorphins may reach the brain cerebrospinal fluid (CSF) in harmful amounts because of their genetically increased, receptor-mediated transcellular passage across the gut epithelial barrier plus decreased catabolism by genetically defective enzymes. A schizophrenia-specific, genetically enhanced affinity for exorphins by opioid receptors influencing dopaminergic and other neurons would permit sustained dysfunction at low CSF exorphin concentrations. Tests of each postulated genetic abnormality are suggested. This model is supported by a variety of evidence, including a significant effect of gluten or its absence on relapsed schizophrenic patients, the high correlation of changes in first admission rates for schizophrenia with changes in grain consumption rates, and the rarity of cases of schizophrenia where grains and milk are rare.

Vascular endothelial invasion via transcellular passage by malignant cells in the primary stage of metastases formation

The entry into the circulation of malignant cells from two metastases forming tumors, i.e., the first phase of metastases formation, was studied in subcutaneous W/Fu AML and B16/BL-6 syngeneic tumor transplants in rats and mice, respectively. Both tumors formed metastases and invaded neighboring tissues. Malignant cells of both tumors entered the circulation by penetrating the intact endothelial cell body. The migration pore thus formed by the migrating cell closed after the cell had reached the intravascular space. Thus, the pathway of malignant cells is transcellular. There was no destructive invasion of the vessel wall by malignant cells, which resulted in patent defects. This mode of entry into the circulation by malignant cells was found in the venules of (and induced by) the tumor and, although with less frequency, in the walls of preexisting veins.

Transcellular migration of lymphocytes through the walls of the smooth-surfaced squamous endothelial venules in the lymph node: Evidence for the direct entry of lymphocytes into the blood circulation of the lymph node

Observations by scanning (SEM) and transmission electron microscopy (TEM) show that the so-called postcapillary or high endothelial venules of the lymph nodes of the mouse are followed distally by venules of wider caliber, lined with a simple squamous endothelium, free from patent apertures and lacking the characteristic surface relief of the venules of immediate postcapillary location ( Cho and De Bruyn, 1979 ). Lymphocytes are in passage through the walls of these squamous endothelial venules. SEM shows that this transmural passage is transcellular, i.e., through the endothelial cell body and not through their cell junctions. A temporary migration pore is formed in the endothelial cytoplasm, which closes after the transcellular lymphocyte passage is completed. The SEM and TEM images of these sites of transcellular passage support the supposition that lymphocytes enter the blood circulation through the walls of these squamous endothelial venules.

An anionic material at the advancing front of blood cells entering the bone marrow circulation

The selective entry of mature blood cells into the peripheral circulation of the bone marrow is a transcellular process. The mature blood cells penetrate the cytoplasm of the endothelial cells lining the myeloid sinuses and form a migration pore in the cell body of the lining cell, which closes after the blood cell reaches the intravascular space. The changes at the surfaces of the cells involved in this selective transcellular process were studied by means of the cationic cell surface markers colloidal iron (CI) and polycationic (high isoelectric point) ferritin (PCF). The anionic cell surface charges resulting from the presence of sialated glycoproteins remain, as shown by the application of these markers at low pH (1.8), evenly distributed at the cell surfaces of both the blood cell and the sinus lining cell. However, there is at the advancing margin of the diapedesing blood cells a marked accumulation of a nonsialated anionic material binding PCF at high pH (7.2). This material first accumulates extravascularly beneath the endothelium at an area of the blood cell surface near the site of the migration pore formation, remains at the cell surface during the initial phases of transcellular passage and disappears, either through shedding in the vascular lumen or through redistribution on the cell surface, when the cell reaches the intravascular space. This anionic material, which is neuraminidase resistant and has a pKa higher than sialic acid, is a characteristic concommitant in the selective transcellular blood cell passage in bone marrow.

An Anionic Material at the Advancing Front of Blood Cells Entering the Bone Marrow Circulation

The selective entry of mature blood cells into the peripheral circulation of the bone marrow is a transcellular process. The mature blood cells penetrate the cytoplasm of the endothelial cells lining the myeloid sinuses and form a migration pore in the cell body of the lining cell, which closes after the blood cell reaches the intravascular space. The changes at the surfaces of the cells involved in this selective transcellular process were studied by means of the cationic cell surface markers colloidal iron (Cl) and polycationic (high isoelectric point) ferritin (PCF). The anionic cell surface charges resulting from the presence of sialated glycoproteins remain, as shown by the application of these markers at low pH (1.8), evenly distributed at the cell surfaces of both the blood cell and the sinus lining cell. However, there is at the advancing margin of the diapedesing blood cells a marked accumulation of a nonsialated anionic material binding PCF at high pH (7.2). This material first accumulates extravascularly beneath the endothelium at an area of the blood cell surface near the site of the migration pore formation, remains at the cell surface during the initial phases of transcellular passage and disappears, either through shedding in the vascular lumen or through redistribution on the cell surface, when the cell reaches the intravascular space. This anionic material, which is neuraminidase resistant and has a pK. higher than sialic acid, is a characteristic concommitant in the selective transcellular blood cell passage in bone marrow.

Lysine transport across rat jejunum: distribution between the transcellular and the paracellular routes.

Transport of lysine across the rat jejunum has been studied measuring transmural fluxes, Jms and Jsm, under short-circuit conditions, influx across the brush-border membrane, Jmc, under open-circuit and voltage-clamp conditions, and steady-state uptake by the isolated mucosa. 1. Jlysmc can be described as the sum of a saturable process with a Kt of 3 mM and a Jmax of 2.25 micromole/cm2.hr and a diffusional component corresponding to a lysine permeability of 0.014 cm/hr. Also Jlysms is well described as the sum of a saturable process and a diffusional contribution described by the same permeability as for Jlysmc. 2. The effects of the transmural p.d. on Jlysmc indicate that at 60 mM this flux includes a diffusional contribution, which corresponds to a lysine permeability of 0.014 cm/hr. 3. The passage of an electrical current across the gut wall changes the electrical conductance as expected for a cation-selective epithelium. The effect of a mucosa to serosa current on the Jms value of mannitol provides confirmation of the expected current effect on transepithelial volume flow. These effects on conductance and solute flux, together with the electrostatic effect on lysine movements, suffice to account for the p.d. effects on Jmc, Jms, and Jsm of lysine. 4. Jlyssm is in a saturable manner stimulated by increasing concentrations of D-glucose. At higher (10 mM) concentrations of lysine this effect leads to a net secretion of lysine. Qualitatively and quantitatively these effects are consistent with the model of a glucose-induced fluid circuit between the mucosal solution and the lateral intercellular spaces. 5. All observations are consistent with a paracellular, transepithelial pathway for lysine, which includes the lateral intercellular spaces. 6. The transport of lysine across the basolateral membrane is analysed. Togethet the data on transcellular passage of lysine are very similar to those reported for rabbit ileum, except that more than one transport process could not be demonstrated.

The intestinal absorption of fatty acid: A biochemical and electron microscopic study

Following the administration of 2 ml of C14-labeled oleic acid to rats by stomach tube, osmiophilic droplets and particles, from 10 to 300 mμ in diameter, were demonstrated in the intestinal lumen. The smaller droplets of fatty acid were frequently found between the microvilli of intestinal epithelial cells and were of the same size range as has been proposed for lipid micelles (10 mμ). The radiochemical examination of the lumen contents revealed that the activity was still present in free fatty acids. Larger osmiophilic droplets, averaging 150 mμ in diameter, were found in cytoplasmic vesicles within the epithelial cells. These findings suggest that electron microscopic visualization of lipid droplets cannot distinguish between fatty acid and mono-, di-, and triglycerides. Therefore, conclusions on the nature of osmiophilic lipid droplets in intestinal absorption must be based upon a correlation with biochemical findings. Chemical and radiochemical findings in the absorption of fatty acid indicate that the fatty acid enters the chyle primarily as triglyceride, that the triglyceride content of the intestinal wall is increased, and that there is a significant transfer of the C14 label from fatty acid to triglyceride at some stage during absorption. These observations mean that at least some of the osmiophilic droplets seen with electron microscopy in the intestinal epithelial cells in fatty acid absorption must be triglycerides. The relationship of these findings to the synthesis of triglyceride from fatty acids during internalization and transcellular passage is discussed.