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Biomedical subjects

M Horster

Publications and source records attributed to M Horster.

At least 37 records · Page 2Linked to original sources
PubMed1980

Aldosterone in vitro restores nephron Na-K-ATPase of distal segments from adrenalectomized rabbits.

Aldosterone, when added in vitro to defined nephron segments, dissected from adrenalectomized rabbits, restores the depressed Na+-K+-ATPase activity in the thick ascending limb of the loop of Henle and in the cortical collecting tubule within 1 h of incubation. The direct effect is specific and, as demonstrated for the cortical collecting tubule, dose-dependent. The time course of aldosterone-mediated Na+-K+-ATPase activation is compatible with the conjecture of changes in the enzyme lipid environment.

Adrenalectomy↗
PubMed1979

Primary culture of mammalian nephron epithelia: requirements for cell outgrowth and proliferation from defined explanted nephron segments.

Nephron segments were dissected from fetal or from early postnatal rabbit kidneys (n = 86) and explanted individually into primary tissue culture. Outgrowth of epithelioid cells and proliferation in monolayers from the collecting tubule and the thick ascending limb of Henle's loop occurred regularly if a special substratum and matrix were used. Media were either supplemented with non-proteins (defined media) or with embryo extract and fetal sera (undefined media). Outgrowth and monolayer spreading were recorded by Differential Interference Contrast Microscopy. Monolayer cells resemble those seen with the same recording technique during tubule in vitro perfusion. Undefined media were essential for growth of convoluted tubule segments from embryonic Nephron Anlagen and outgrowth of cells from proximal straight tubules, in contrast to the distal nephron segments. The specific functional and morphological properties of cells derived from primary culture of nephron segments are under study.

Animals↗
PubMed1979

Application of differential interference contrast with inverted microscopes to the in vitro perfused nephron.

The study of in vitro perfused individual nephron segments requires a microscope which provides: (1) easy access to the specimen for measurement of cellular solute flux and voltage; (2) an image with high resolution and contrast; (3) optical sectioning of the object at different levels; and (4) rapid recording of the morphological phenomena. This paper describes an example of commercially available apparatus meeting the above requirements, and illustrates its efficiency. The microscope is of the inverted type (Zeiss IM 35) equipped with differential-interference-contrast (DIC) with a long working distance, and an automatically controlled camera system. The microscopic image exhibits cellular and intercellular details in the unstained transporting mammalian nephron segments despite their tubular structure and great thickness and makes obvious function-structure correlations (e.g. cell volume changes); luminal and contraluminal cell borders are well resolved for controlled microelectrode impalement.

Animals↗
PubMed1979

Nephron electrolyte transport and sodium-potassium adenosine triphosphatase activity: influence of nicotine in rat and rabbit.

1. The influence upon mammalian renal epithelial transport of L-nicotine was studied in different types of experiments. 2. The kidney in situ (rat), when infused with nicotine (1 mg hr-1 kg-1 I.V.), lowered its absolute and fractional K+-absorption significantly and reversibly, but Na+-absorption did not change. Effects on glomerular function and an irreversible effect upon epithelial Na+ and K+ absorption were prevailing at higher infused amounts (10 or 50 mg hr-1 kg-1). 3. Single dissected nephron segments (collecting tubule, rabbit) were perfused in vitro, and the Na+ and K+-transtubular net flux was measured while L-nicotine (50 ng/ml.) had been added to the contraluminal side of the epithelium. Both, Na+-absorption and K+-secretion were decreased reversibly. 4. The activity of the Na+-K+-activated ATPase was significantly decreased in the cortical collecting tubule and in the proximal convoluted tubule of the rabbit after incubation of single in vitro dissected nephron segments with L-nicotine (50 or 100 ng/ml.). In contrast, nicotine added to a homogenate of renal cortical tissue had no effect on the Na+-transport enzyme or on key enzymes of glycolysis and gluconeogenesis. 5. These observations on the kidney in situ and on defined, perfused and non-perfused nephrons in vitro suggest that L-nicotine has dose-dependent, direct epithelial and mediated systemic effects on mammalian renal ion transport.

Animals↗
PubMed1978

In vitro perfused, non-isolated small intestine: ontogeny of transmural hydraulic permeability.

Net fluid flux and transmural hydrostatic hydraulic conductance (Lp) were measured in the rat ileum during postnatal ontogeny, utilizing a refined in vitro, capillary-perfused (non-isolated) preparation for free-flow studies. Volume absorption at low transmural pressure gradient (1-2 cmH2O) was 0.99 +/- 0.22 ml/g wet weight.hr in the mature ileum and 1.55 +/- 0.42 ml/g wwt.hr in the differentiating intestine. Hydrostatic hydraulic conductance of the mature ileum was 0.76 microliter/cm2.cm H2O.hr, indicating that normal hydrostatic pressure gradients are not important for modulation of intestinal absorption. In contrast, Lp was 3.82 microliter/cm2.cmH2O.hr in the differentiating ileu, suggesting a significant contribution of pressure-dependent solvent drag to isotonic solute absorption.

Aging↗
PubMed1977

Determination of electrolytes in small biological fluid samples using energy dispersive x-ray microanalysis.

A technique is reported for the application of the energy dispersive X-ray microanalysis for the simultaneous determination of electrolytes in picoliter samples of biological fluids. The preparation is characterized by the use of thin films as a specimen support. Using this arrangement, the X-rays generated in the support are kept to a minimum. At an acceleration voltage of 25 kV the specimen preparation can be regarded as 'thin', i.e. the intensity of an emitted characteristic radiation is almost uninfluenced by the gross element composition, and, therefore, is only dependent upon the content of elements. Quantification was achieved by comparing the intensities of the characteristic radiations with that of a standard. Electrolyte concentrations of 1 mM can be detected with an accuracy of 0.1 mM SD.

Animals↗
PubMed1977

Na-K-activated ATPase: activity maturation in rabbit nephron segments dissected in vitro.

Single, defined nephron segments were dissected in vitro from fresh slices of neonatal and mature rabbit kidney. Na-K-ATPase was quantified for six different tubule segments with an ultramicromethod. The enzyme distribution pattern in the neonatal nephron was similar to that in the mature nephron. Activity in distal segments was 2-5 times higher than proximal tubule activity referred to tissue dry weight, and 2 times higher referred to tubule length. Neonatal enzyme activity was lower than mature in all segments. Some segments carried only 23% of mature activity. Enzyme activity in the proximal convoluted tubule was constant during maturation when referred to the basal and lateral membrane area measured in the same developmental stages. In vitro activities of these tubules were similar to the enzyme activity measured previously in freeze-dried slices. The Vmax during development of Na-K-ATPase was higher by a factor of 5 in the mature tubule, whereas the Km was identical in the neonatal and mature tubule. The ouabain-insensitive ATPase did not show a maturational activity change.

Adenosine Triphosphatases↗
PubMed1977

Maturation of diluting capacity in loop of Henle of rat superficial nephrons.

The postnatal development of renal diluting capacity was studied by free-flow micropuncture and by microdissection of single superficial loops of Henle in rats kept on a high salt diet. Total renal filtration rate, sodium absorption, total solute excretion, and systemic arterial pressure were monitored during single nephron evaluation at two maturational stages (12-15 days and 27-35 days postnatal). Nephron filtration rates were identical when measured in early distal and late proximal segments of the same nephron. Absolute fluid absorption between these sites increased by a factor of 2.5, whereas loop fractional absorption of the volume load changed from 38.1 +/- 6.9 to 49.8 +/- 4.8% (SD), while proximal volume delivery to the loop increased from 4.33 +/- 1.12 to 7.14 +/- 0.65 nl/min. Simultaneously, the osmolarity of early distal fluid (8.8% of distal length) decreased significantly from 284 + 19.8 to 180.9 +/- 18.2 mosmol/liter during maturation. This study suggests that the ability of the loop of Henle to generate hypotonic fluid is attained only gradually during ontogeny. Volume absorption in the loop of Henle increases disproportionately to the loop volume load.

Absorption↗
PubMed1977

Nephron function and perinatal homeostasis.

A) The proximal nephron and perinatal regulation of extracellular volume. 1. The glomerular capillary permeability coefficient (Kf) changes mainly because of an increasing capillary hydraulic conductance (Lp) within the autoregulatory range of renal perfusion pressure. 2. Proximal tubule hydrostatic hydraulic conductance and response to transmural protein concentration gradients is high during perinatal adaptation. 3. Proximal tubule paracellular shunt pathways are more important for absorption during differentiation than at maturity. 4. Basolateral membrane area of the single epithelial segment (10(-6) micron2 mm-1) increases and the typical basal labyrinth architecture develops. 5. The activity of the transport enzyme Na-K-ATPase increases in parallel to the basolateral membrane area to result in a constant number of enzyme sites during normal ontogeny. B) The distal nephron and perinatal regulation of extracellular osmotic activity. 6. Inner medullary urea content increases at osmotic equilibrium between interstitium and collecting duct. 7. The loop of Henle gradually dilutes the isotonic luminal fluid in the course of perinatal differentiation. 8. The thick ascending segment of the loop of Henle differentiates its anisotonic transport by increasing the Na-Chloride transport at constant hydraulic conductivity. 9. Ultrastructure and N-A-K-ATPase activity of the diluting segment (TAL) change greatly during ontogeny. 10. The centrifugal pattern of renal maturation from the juxtamedullary towards the superficial cortical layers leads to an intracortical profile of structure and function.

Adenosine Triphosphatases↗
PubMed1976

Mechanisms of fluid absorption during proximal tubule development.

UNLABELLED: 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. CONCLUSIONS: 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.

Absorption↗
PubMed1971

ostnatal development of renal function: micropuncture and clearance studies in the dog.

Postnatal renal development was studied in dogs between 2 and 77 days. Single, superficial nephrons were evaluated by micropuncture, concurrently with measurements of total renal function and morphometric analyses in the same animals. Glomerular filtration rate for the entire kidney increased linearly from 0.13 ml/min per g kidney weight at 2 days to 0.91 at 77 days. Extraction of p-aminohippurate increased from about 20 to 80%, and renal plasma flow per g kidney weight, measured as Cpah/Epah, increased threefold during the same period. Filtration fraction increased to the mature value during the first half of the postnatal period studied. The clearance of urea per unit of renal mass increased with age, whereas the fraction of filtered urea reabsorbed declined during the early part of the postnatal period. The pattern of fractional urea reabsorption may be due mainly to increased medullary recycling of urea and to a rise in the reabsorption of water from the medullary collecting duct. Urine osmolality was higher than plasma from birth onward and rose with age. Osmolal equality of collecting duct fluid and medullary interstitium reflected mature vasopressin (ADH)-induced water permeability. The rise in urinary concentration was predominantly due to increasing medullary sequestration of urea. Glomerular filtration rate of the superficial nephron increased from 3.2 nl/min at 21 days, when subcapsular nephrons were uniformly patent, to 23.1 at 77 days. Despite this rise in filtered load, fractional reabsorption of sodium and water in superficial proximal tubules was constant and at the mature level from the onset of intratubular perfusion. Changes in arterial plasma protein concentration, in filtration fraction, and in the hydrostatic pressure gradient between proximal tubule and peritubular capillary may interact to maintain glomerulotubular balance. The data, together with results of an accompanying morphological study, demonstrate a sequence of coordinated changes during postnatal renal maturation.

Absorption↗