Franz Beck

Osmoregulation of renal papillary cells

Element concentrations were determined in various extra- and intracellular compartments of the rat renal papilla in antidiuresis and after furosemide-induced diuresis using electron microprobe analysis to elucidate further how the cells adapt osmotically to different osmolatities. In antidiuresis and diuresis the sum of intracellular cations (sodium and potassium), accompanying anions and urea was insufficient in both cases to provide cell osmolatities similar to those in extracellular compartments. This finding provides further evidence that the papillary cells achieve osmoadaptation to widely differing extracellular electrolyte concentrations mainly by varying the cellular concentrations of osmotically-active substances other than urea and electrolytes.

Cl transport across the basolateral membrane in frog skin epithelium

Cellular Cl concentrations were determined by electron microprobe analysis to obtain further insight into the Cl transport across the basolateral membrane of the frog skin epithelium. Cl-free media on the serosal side led in all epithelial layers within 1 h to a decrease in cellular Cl concentration from about 40 to 15 mmol/kg wet wt, whereas the application of Cl-free solutions or amiloride to the apical side had no effect. Na-free media, furosemide or bumetanide on the serosal side had little effect on cellular Cl but abolished the Cl-reuptake into Cl-depleted cells. It is concluded that cellular Cl concentration is maintained above electrochemical equilibrium by a co-transport system, which is relatively silent under control conditions.

Intracellular elemental concentrations in renal tubular cells. An electron microprobe analysis

SummaryIn order to be able to examine the processes involved in transepithelial transport in tissues, which are not composed of a single cell type, methods are required, which permit analysis at a cellular level. The technique of electron microprobe analysis permits the intracellular concentrations of many elements to be determined simultaneously in various portions of the cell. The application of this method to renal cortical tissue has shown that the best estimates of the cytoplasmic concentrations are to be obtained in regions close to the nucleus, farthest from the basolateral infoldings and microvilli, which separate the intracellular environment from the extracellular space. The nuclear concentrations of Na and K do not differ from those in the surrounding cytoplasm, although those of P and C1 are somewhat higher in cytoplasm. The intracellular element concentrations in the different cell types vary somewhat, proximal tubular cells contain higher concentrations of Na and C1 and lower ones of P than distal tubular cells. Following ischaemia, a manoeuvre know to result in a disturbance of intracellular electrolytes, Na was observed to rise and K to fall only in the non-surface cells of kidneys exposed to the air, but in all cells, if the kidneys were kept air-free in an atmosphere of N2. The proximal and distal tubular cells showed a variable resistance to ischaemia, the distal tubular cells being much more resistant. Despite the severity of the electrolyte disturbance following ischaemia, the intracellular composition was completely restored one hour after re-introducing renal blood flow.

Na transport compartment in rabbit urinary bladder

Electron microprobe analysis was used to determine cellular electrolyte concentrations in rabbit urinary bladder. Under control conditions the mean cellular electrolyte concentrations were for Na 11.6±2.0, for K 124.1±15.3, and for Cl 26.0±5.1 mmol/kg wet weight. The dry weight content was 19.0±2.0 g/100 g. Inhibition of the Na/K-pump with ouabain resulted in drastic changes of the cellular element concentrations. Similar changes also occurred when in addition to ouabain the apical side was kept Na-free. In all epithelial layers the Na and Cl concentrations increased by 90 and 30 mmol/kg wet weight, whereas the K concentration and the dry weight content decreased by 90 mmol/kg wet weight and 6 g/100 g wet weight, respectively. With Na-free choline-Ringers solution on the basal side ouabain led to a decrease in the K concentration by about 60 mmol/kg wet weight while the Na and Cl concentrations remained unchanged. These data indicate that the basolateral membrane is permeable to Na, choline, Cl, and K. Nystatin produced drastic changes in the cellular electrolyte concentrations when Na- or Rb-sulfate Ringers solutions were present on the apical side. With Na-sulfate Ringers solution the Na concentration increased by about 25, the Cl concentration by 30 mmol/kg wet weight and the dry weight content decreased by 4.5 g/100 g, respectively. With Rb-Ringers solution about 20 mmol/kg wet weight of the cellular K was exchanged against Rb. The concentration changes were identical in all epithelial layers supporting the idea that the rabbit urinary bladder represents a functional syncytium with regard to the transepithelial Na transport.

Na Transport in Rat Gastric Mucosa: An Electron Microprobe Analysis

To identify and characterize the cells involved in Na absorption in the mammalian stomach, the electrolyte concentrations of surface and gland cells were determined in isolated rat gastric mucosa usin

Localization of transport compartments in turtle urinary bladder

To characterize different transport compartments in the urinary bladder epithelium of postabsorptive turtles, the electrolyte composition of individual cells was determined using electron microprobe analysis. After blocking the transepithelial Na transport, the short-circuit current decreased from positive to negative values (from 26.5±17.7 to −3.9±2.9 after ouabain and from 25.4±17.2 to −8.0±5.1 μA/cm2 after amiloride). Whereas under control conditions the Na and K concentrations were similar in all cell types and the same was true for Cl in most of the cells, some cells exhibited very low Cl concentrations. The epithelial cells were subdivided according to their electrolyte composition into ouabain-sensitive and ouabain-insensitive ones. In the ouabain-sensitive cells, which made up the majority of epithelial cells and showed a relatively high Cl concentration (about 36 mmol/kg wet weight), the Na concentration increased after ouabain by about 90 mmol/kg wet weight and the K concentration decreased by a similar amount. Since these alterations could largely be prevented when amiloride was applied before ouabain, it is suggested that the granular and basal cells form a syncytial Na transport compartment similar to that in other multilayered epithelia. The ouabain-insensitive cells, in which almost no alteration in Na and K concentrations was observed after ouabain, were subdivided into a Cl-rich (34.6±7.6 mmol/kg wet weight) and a Cl-poor (12.0±5.6 mmol/kg wet weight) population. Since in these cells no large mucin granules were detectable, they are regarded as carbonic anhydrase-rich cells involved in H and HCO3 transport.

Chapter 8 Quantitative Determination of Electrolyte Concentrations in Epithelial Tissues by Electron Microprobe Analysis

Publisher Summary This chapter describes the methods and data on the intraepithelial electrolyte concentrations in frog skin and rat kidney by electron microprobe analysis (EMA) of thin freeze-dried cryosections. The EMA data obtained from the analysis of transepithelial sodium (Na) transport in frog skin are in good agreement with the chemical analysis of isolated epithelial cells that have been jet-washed in Na-free solution to reduce the amount of extracellular Na. The Na transport compartment comprises all living epithelial layers forming a functional syncytium, where Na enters the epithelium passively across the outer facing membranes of the stratum granulosum, passes via intercellular junctions into deeper epithelial layers, and is actively extruded across the basolateral membranes into the intercellular spaces, from which it diffuses toward the corium. Analyses of electrolyte concentrations in rat kidney tubular cells showed differences in the electrolyte concentrations in proximal and distal kidney tubules in the control that may reflect a functional inhomogeneity in the nephron segments after short-time ischemia—for example, differences in the cellular energy metabolism and/or transport properties of the apical or basolateral cell membranes.

Electroneutral Acid Secretion in Frog Gastric Mucosa: An Electron Microprobe Analysis

To elucidate the mode of H secretion in the intact gastric mucosa, the cellular element concentrations and Rb uptake by individual surface and oxyntic cells of the short-circuited isolated frog gastric mucosa (Rana esculenta, Rana temporaria) were determined using electron microprobe analysis. The H secretion rate was measured by the pH stat method. Under normal conditions both surface and oxyntic cells exhibited typical cellular electrolyte patterns with low Na and high K concentrations. The apical parts of surface cells, in which large mucus-containing vesicles are located, were characterized by relatively high S and Ca concentrations. Histamine-stimulated H secretion in the gastric mucosa of R. esculenta and R. temporaria was about 2.0 and 0.5 µmol/cm2·h, respectively. In the presence of 20 mM Rb in the mucosal bathing solution, a substantial portion of cellular K was exchanged for Rb in oxyntic but not in surface cells. This K-Rb exchange was almost completely abolished by inhibition of H secretion with omeprazole indicating a specific H-Rb(K) exchange across the apical membrane of oxyntic cells. At a low H secretion of about 0.5 µmol/cm2·h about 70% of the H secretion rate could be matched by the omeprazole-inhibitable Rb uptake rate. Accordingly H secretion seems to be accomplished by an electroneutral H-Rb(K) exchange. The negligible Rb uptake into oxyntic cells at a mucosal Rb concentration of 5 mM might be explained by K recirculation across the mucosal membrane via a K conductance and the H-K-ATPase.