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M Bundgaard

Publications and source records attributed to M Bundgaard.

50 records · Page 3Linked to original sources
PubMed1982

Structure of Necturus gallbladder epithelium during transport at low external osmolarities.

Gallbladders transport isotonically over a wide range of osmolarities. This ability has been assumed to depend on the geometry of the lateral intercellular spaces. We report that this geometry in the Necturus gallbladder varies extensively with the external osmolarity and depends in vitro on the integrity of the subepithelial tissues. The structure of the living epithelium was studied by Nomarski light microscopy while ultrastructural effects were revealed by electron microscopy. The short-term effects (less than 60 min) of low external osmolarities were: 1) the cells became bell-shaped with an increased cell height measured centrally, 2) lateral intercellular spaces lost their convoluted character; and 3) numerous membrane-bound cavities appeared in the cells. Furthermore, long-term exposure to the low external osmolarities caused an uneven density of epithelial cells. With subepithelial tissues intact, blistering of the epithelium cell layer was evident. Qualitative electron-microscopic data indicate that the membrane of the cavities was recruited from the basolateral cell membrane. This agrees well with light-microscopic observation that the cavities were initiated as invaginations of this cell membrane.

Animals↗
PubMed1981

A glial blood-brain barrier in elasmobranchs.

The blood-brain interface in elasmobranchs was examined using physiological and anatomical techniques. Electrolyte analyses of plasma and cerebrospinal fluid (CSF) in control fish and in fish with elevated plasma cation concentration (Ca, Mg or K) demonstrated homeostasis of CSF calcium and magnesium concentrations in dogfish and skates and of CSF potassium concentration in dogfish. In contrast, CSF potassium concentration was not regulated independent of plasma potassium concentration in skates. Ultrastructural examination of the blood-brain barrier in skates showed that brain capillaries are fenestrated and intravenously injected horseradish peroxidase penetrates readily across this endothelium into the basement membrane. Further penetration of tracer into the neuropil is prevented by tight junctions between perivascular glial cells. Results indicate that two hallmarks of the blood-brain barrier--impermeability and homeostatic transport systems--can be localized to the perivascular glial sheath in elasmobranchs. The functional and structural similarity of this glial membrane to a transporting epithelium is discussed.

Animals↗
PubMed1981

Impermeability of hagfish cerebral capillaries to radio-labelled polyethylene glycols and to microperoxidase.

The rate and extent of penetration of radiolabelled polyethylene glycols (900 and 4000 daltons) from plasma into brain was examined in the Atlantic hagfish (Myxine glutinosa), a primitive vertebrate, and, for comparison, in the rat. Tracer penetration into brain was limited to a similar extent in hagfish and in rats, indicating a basic similarity between the two species in the blood-brain barrier to polar non-electrolytes. The permeability of hagfish brain capillaries to the electron microscopic tracer microperoxidase (2000 Daltons) was also examined. Intravenously injected microperoxidase remained confined to the capillary lumen and was not found in the basal lamina or surrounding brain parenchyma. In contrast to an earlier study, these results indicate that the hagfish has a blood-brain barrier to hydrophilic molecules larger than 900 Daltons. It is concluded that a blood-brain barrier is a general characteristic of all vertebrates.

Animals↗
PubMed1981

Localization of sodium pump sites in cat pancreas.

1. Cat pancreases were exposed to [3H]ouabain either by perfusion, or by incubation of slices, with Krebs--Henseleit bicarbonate solution containing [3H]ouabain, and [3H]ouabain binding sites were localized by light microscopical autoradiography. 2. Acinar cells were found to possess only a few [3H]ouabain binding sites located on the basolateral plasma membranes. 3. The epithelial cells lining the intercalated and interlobular ducts were heavily labelled. The [3H]ouabain binding sites were located on the basolateral membranes. 4. Since secretion of pancreatic juice can be abolished by ouabain, it is concluded that the duct cells, especially those of the numerous small (intercalated) and intermediate-sized (interlobular) ducts are responsible for pancreatic secretion of electrolytes and water. 5. The localization of the (Na+ + K+)-activated ATPase to the basolateral membranes of the cells excludes a direct role of the transport enzyme in the secretion of Na+. However, a model is proposed where the Na+ + K+)-activated ATPase plays a crucial, though indirect role in pancreatic secretion of electrolytes and water.

Animals↗
PubMed1981

Horseradish peroxidase and microperoxidase. Their purity and binding to serum proteins.

Buffer solutions of commercially available batches of the electron microscopic enzyme tracers, horseradish peroxidase (HRP, mol wt = 40,000) and microperoxidase (MP, mol wt = 2,000), were investigated by gel filtration. The elution profiles of the HRP and MP solutions together with estimates of the peroxidatic activity of the collected fractions indicated that HRP was homogeneous with respect to molecular weight, while MP contained high molecular weight impurities with peroxidatic activity. Serum samples from four different species of tracer-injected animals (hagfish, lamprey, frog, mouse) and from control animals were investigated with the same techniques. No binding between HRP and the serum proteins or degradation of HRP was detected; whereas, MP circulated predominantly bound to serum proteins in all the investigated animals. The number average molecular weights of aqueous solutions of HRP and MP determined by vapor osmometry were 9,000 and 1,000, respectively. The results emphasize that protein binding should be evaluated when MP is used as an electron microscopic tracer. In addition, the finding that HRP and MP solutions have a much higher osmotic activity than the molecular weights of the tracers would suggest should be taken into consideration, especially when bolus injections into animals are performed.

Animals↗
PubMed1980

ATP-dependent Ca2+ accumulation by microvesicles isolated from bovine neurohypophyses.

Microvesicles with and without coats were isolated from bovine neurohypophyses by a series of ultracentrifugation steps. They were similar to microvesicles previously isolated from brain. In the presence of ATP and Mg2+, the microvesicles accumulated calcium. Oxalate stimulated and the Ca2+ ionophore A23187 inhibited calcium accumulation. In the presence of Ca2+ and Mg2+ the microvesicles also demonstrated ATPase activity. As judged by SDS electrophoresis in polyacrylamide gels microvesicle protein composition was very different from that of neurosecretory granules, suggesting that they are not granule membranes "retrieved" after exocytosis. They may have an important function in regulation of Ca2+ ion concentration.

Adenosine Triphosphatases↗
PubMed1980

On the anatomic relation of choroid plexus to brain: a comparative study.

The size of choroid plexuses and cerebral ventricles relative to brain varies widely among vertebrates. The functional significance of this variability has attracted little attention since Herrick's original proposal that large choroid plexuses might enhance oxygen delivery to the brain and therefore be of adaptive value in the transition of vertebrates from water to air breathing. We compared choroid plexus and brain weight or ventricular and brain volume in 40 species from nine vertebrate groups. Both choroid plexus weight and ventricular volume were unrelated to brain size. Plexus weight ranged from 0 to 5.2% of brain weight and ventricular volume from 0.9 to 132% of brain volume. Amid this diversity the dipnoans, chondrosteans, holosteans, amphibians, and crossopterygian examined in this study are exceptional in uniformly having large plexuses. The adaptive significance of large choroid plexuses may lie in the presence of specific homeostatic mechanisms and their role in the response to the increases in PCO2 that accompany the transition to air breathing.

Animals↗
PubMed1979

Impermeability of hagfish cerebral capillaries to horseradish peroxidase. An ultrastructural study.

Brain capillaires and their permeability to intravenously injected horseradish peroxidase, HRP, (MW: 40,000) were examined electron-microscopically in an attempt to find a structural explanation for the poorly developed blood-brain barrier in the hagfish, Myxine glutinosa. In particular, it was the aim of this study to examine the role of the numerous endothelial vesicles and tubules in the transport of this tracer between blood and brain. Many of the vesicles and tubules were found to be in continuity with the luminal or abluminal surfaces, but tubules generating channels through the endothelial cells were never observed. The cleft between adjacent endothelial cells was obliterated by punctate junctions. HRP, which was aloowed to circulate for up to 35 min, was not found in the basal lamina or in the surrounding brain parenchyma. Few of the luminal vesicles and tubules were marked by the tracer. In the intercellular cleft HRP was stopped by the junctions. It is concluded that the hagfish like other vertebrates has a blood-brain barrier to HRP, and the numerous vesicles and tubules occurring in hagfish brain endothelium are not involved in the transendothelial transport of this macromolecule.

Animals↗
PubMed1979

Endothelial plasmalemmal vesicles as elements in a system of branching invaginations from the cell surface.

In electron microscopy studies of the endothelial vesicles in frog mesenteric capillaries, an accidental observation was made concerning vesicular organization. When tannic acid was added to already fixed tissue, the mordant reached apparently free vesicles in the cytoplasm under conditions in which vesicular movement was excluded and in which the impermeability of the cell membranes was preserved. This indicates a spatial continuity between the vesicles and the cell exterior. It is proposed that cytoplasmic vesicles in endothelial cells are elements of branching, permanent or semipermanent invaginations of the plasmalemma.

Animals↗
PubMed1977

Localization of sodium pump sites in cat salivary glands.

1. Cat submandibular glands were perfused with Locke solution containing [3H]ouabain. In some experiments additional medium was given by retrograde intraductal injection. 2. [3H]ouabain binding sites were localized by light microscopical autoradiography and the findings compared with the electron micrographs. 3. The cells of the striated ducts were heavily labelled with [3H]ouabain, predominantly in the contraluminal parts. 4. At the acinar level moderate amounts of [3H]ouabain were found in relation to the plasma membranes of the demilunar cells. The central acinar cells were found to be virtually devoid of [3H]ouabain. 5. Electron microscopy revealed that the demilunar cells possessed long, tortuous intercellular spaces separated from the secretory canaliculi by junctional complexes. In contrast, the membranes between adjacent central acinar cells were fairly straight. 6. It is concluded that the striated ducts play a dominant role in the ductal reabsorption of sodium, and that the transport is probably mediated by a (Na+ + K+)-activated ATPase. The findings on the acinar level are in agreement with the view that the primary saliva is formed predominantly by the demilunar cells. The role of a (Na+ + K+)-activated ATPase in this process is unclear.

Adenosine Triphosphatases↗