Biomedical subjects

R Rick

Publications and source records attributed to R Rick.

At least 19 recordsLinked to original sources

PubMed1994

Short-term bromide uptake in skins of Rana pipiens.

Intracellular ion concentrations were determined in split skins of Rana pipiens using the technique of electron microprobe analysis. Based on the 1 min Br uptake from the apical bath, two types of mitochondria-rich (MR) cells could be distinguished: active cells which rapidly exchanged their anions with the apical bath and inactive cells which did not. Br uptake and frequency of active MR cells were closely correlated with the skin conductance, gt. Replacing Cl in the apical bath with an impermeant anion significantly lowered gt and the Br uptake and Na concentration of active cells. Even larger reductions were observed after apical amiloride (0.1 mM). The inhibition of the Br uptake was reversible by voltage clamping (100 mV, inside positive). Cl removal and amiloride also led to some shrinkage of active cells. The results suggest that the active cell is responsible for a large part of gt. Inactive MR cells had much lower Br and Na concentrations which were not significantly affected by Cl removal, amiloride, or voltage clamping. Principal cells, which represent the main cell type of the epithelium, showed only a minimal Br uptake from the apical side which was not correlated with gt. Moreover, Cl removal had no effect on the Na, Br, and Cl concentrations of principal cells.

Amiloride↗

PubMed1994

pHi determines rate of sodium transport in frog skin: results of a new method to determine pHi.

The pH of the isolated frog skin epithelium was determined on a cellular and subcellular level based on the distribution of a weak organic acid, 4-bromobenzoic acid. The indicator is detectable by X-ray microanalysis due to the presence of an element label. The results show that the pH of principal cells, but not the Na concentration, is closely correlated with the rate of transepithelial Na transport. Acidification leads to an inhibition of Na transport, regardless of whether the change was spontaneous or experimentally induced. Under the conditions of this study, the pH of principal cells was not well regulated. At a bath pH of 7.0, large pH differences between the cell layers were detectable. In mitochondria-rich cells, the pH was a function of the intracellular Cl concentration but not the Na transport rate. The cytoplasmic pH consistently exceeded the nuclear pH. The nuclear-cytoplasmic pH differential in principal cells amounted to 0.3 pH units, which is equivalent to a nuclear potential of -17 mV. The results support the view that the intracellular pH (pHi) is an important regulator of transepithelial Na transport. Regulation is primarily achieved at the level of the apical Na channel, making the Na influx the rate-limiting step in Na reabsorption.

Animals↗

PubMed1993

Ion concentration changes in renal cells during regulatory volume decrease.

Electron-probe microanalysis was employed to follow ion concentration changes during regulatory volume decrease. The measurements were performed on isolated tubule bundles, which were dissected from medullary rays of New Zealand White rabbit kidneys. Cell swelling and subsequent regulatory volume decrease were induced by incubating the bundles in 190 mosM medium; control bundles were incubated in 290 mosM medium. Under both conditions, the detectable ions accounted for approximately 80% of the intracellular osmolarity. All cells lost significant amounts of Na, K, and Cl during cell volume regulation. While in the proximal straight tubule more than one-half of the ions lost were Na and Cl, in principal and intercalated cells of the cortical collecting duct and in the thick ascending limb the losses of Na and Cl played only a minor role. The efflux of Na and K greatly exceeded the Cl efflux, suggesting the loss of an additional undetectable anion (bicarbonate). Separate measurements in the nucleus, cytoplasm, and several cellular organelles revealed some inhomogeneity of the subcellular ion distribution.

Animals↗

PubMed1992

Intracellular ion concentrations in the isolated frog skin epithelium: evidence for different types of mitochondria-rich cells.

Intracellular ion concentrations were determined in split skins of Rana pipiens using the technique of electron microprobe analysis. Under control conditions, principal cells and mitochondria-rich cells (MR cells) had a similar intracellular ion composition, only the Cl concentration in MR cells was significantly lower. Inhibition of transepithelial Na transport by low concentrations of ouabain (2 x 10(-6) M, inner bath) resulted in a Na concentration increase of principal cells from 10.9 to 54.3 mmol/kg wet wt. The increase was completely abolished by simultaneous application of amiloride (10(-4) M, outer bath). Amiloride alone resulted in a significant decrease of the Na concentration to 6.1 mmol/kg. w.w. Among MR cells, two different groups of cells could be distinguished; cells that showed a Na increase after ouabain which was even larger than that in principal cells and cells that did not respond to ouabain. In about half of all ouabain-sensitive MR cells the Na increase could be prevented by amiloride. According to these results, a subpopulation of MR cells displays the transport characteristics expected for a transepithelial Na transport compartment, an apical amiloride-sensitive Na influx and a basal ouabain-inhibitable Na efflux. Given the small number of cells, however, it is unlikely that this subtype of MR cells contributes significantly to the overall rate of transepithelial Na transport.

Amiloride↗

PubMed1992

Secretion of K and Cl across colonic epithelium: cellular localization using electron microprobe analysis.

Electron microprobe analysis of quick-frozen distal colonic epithelium from guinea pig was used to locate the cells responding to secretory stimuli. Concentrations of Na, K, and Cl were similar for cells of surface and crypt in the unstimulated state, 8, 149, and 46 mmol/kg wet weight, respectively. Stimulation of either K and Cl secretion with prostaglandin E2 or K secretion alone with epinephrine increased Na to approximately 12 mmol/kg wet weight in crypt cells but not in surface cells or cells in the crypt neck. This result supports the location of ion secretory cells in the lower two-thirds of the crypt. In the vacuoles of crypt columnar cells, stimulation of KCl secretion decreased K, S, Mg, and Ca and increased Na and Cl, indicative of the concomitant release of vacuole contents. Mucin granules in crypt goblet cells contained more S and Mg than granules in surface goblet cells. These findings support the concept of differentiation in ion and macromolecular secretory function along the axis from crypt to surface epithelium.

Animals↗

PubMed1990

Effect of amiloride on electrolyte concentrations and rubidium uptake in principal and mitochondria-rich cells of frog skin.

The role of mitochondria-rich cells (MR cells) in transepithelial Na transport was investigated by determining electrolyte concentrations and Rb uptake in individual cells of frog skin epithelium using electron microprobe analysis. Measurements were performed under control conditions and after blocking the transepithelial Na transport with amiloride. Under control conditions, Na and Cl concentrations of MR cells scattered much more than those of principal cells and ranged from a few up to more than 30 mmol/kg wet weight. Rb uptake from the basal side into individual MR cells also showed a large variation and was, on the average, much less pronounced than into the principal cells. In principal cells, amiloride reduced the Na concentration and Rb accumulation. In contrast, no effect was observed upon electrolyte concentration and Rb uptake of MR cells. Rb uptake was correlated to the Na concentration of MR cells both under control conditions and after amiloride. It is concluded that, in contrast to the principal cells, MR cells are not involved in amiloride-sensitive transepithelial Na transport and that their Na/K-pump activity is very low.

Amiloride↗

PubMed1990

Ion concentrations in the rat CCD: differences between cell types and effect of alkalosis.

We have previously shown that the isolated perfused cortical collecting duct (CCD) from chloride-depleted alkalotic (CDA) rats continues to secrete HCO3 for up to 3 h. To determine whether the sustained alteration in transport was associated with changes in intracellular ion concentrations, we performed energy-dispersive X-ray microanalysis in microdissected tubule bundles obtained from CDA rats and rats with normal acid-base status (CON). Before analysis, the bundles from both groups were incubated for 1 h in vitro in a modified Ringer solution (pH 7.4, 105 mM Cl). Principal (PC) and intercalated cells (IC) of the CCD from CON animals differed in the nuclear concentration of Na (17.0 vs. 24.7 mmol/l cell water), K (192.5 vs. 177.0 mmol/l cell water), and Cl (17.8 vs. 47.8 mmol/l cell water). Cells of the cortical thick ascending limb of Henle (CTAL) had the lowest Na and Cl values (11.5 and 14.8 mmol/l cell water, respectively). CDA resulted in no systematic Cl changes. In the IC the nuclear Na concentration was significantly increased (32.0 vs. 24.7 mmol/l cell water) and in all cells a small reduction in K concentration was detectable. These findings suggest that 1) the different transport functions of IC, PC, and CTAL are associated with differences in the intracellular ion composition, and 2) the sustained HCO3 secretion seen in CCD from CDA rats cannot be explained as the result of intracellular Cl depletion.

Alkalosis↗

PubMed1990

Studies of epithelial electrolyte transport by marker ions.

The paper reviews several recent studies in which marker ions, such as Rb and Br, were used to identify ion transport pathways and membrane properties in epithelia. In the frog skin epithelium, using Rb as a substitute for K, Cl transport mechanisms across the basolateral membranes of principal cells were studied. The data suggest that intracellular Cl is maintained above electrochemical equilibrium by an Na-K-2Cl cotransport system which, under non-stimulated conditions, is normally quiescent. In toad and frog skins, the route of transepithelial Cl movement was investigated. A subpopulation of mitochondria-rich cells demonstrated a ready exchange of Br with the apical and basal bathing media, consistent with the view that these cells constitute a transcellular anion shunt. Moreover, voltage-activation resulted in an increased Br uptake from the apical bath. Nevertheless, because of the very small number of these cells, it may be questioned whether the mitochondria-rich cell constitutes the only shuntpathway for Cl. In other studies, Rb uptake was employed to measure the Na/K-pump activity. In principal cells of the frog skin epithelium, amiloride inhibited Rb uptake and lowered Na concentration, supporting the view that this cell type is engaged in amiloride-sensitive Na transport. In contrast, no significant changes in the Rb, Na, and Cl concentration of mitochondria-rich cells were detectable. Studies with Rb as marker ion in the rabbit urinary bladder revealed that the epithelium behaves like a functional syncytium with regard to transepithelial ion transport.

Amiloride↗

PubMed1989

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 microA/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.

Amiloride↗

PubMed1989

Metabolic control of intracellular ion concentrations in the frog skin epithelium.

The effects of the metabolic inhibitors 2-deoxy-d-glucose and monofluoroacetate on intracellular ion concentrations and Na transport rate were investigated in the isolated frog skin epithelium of Rana pipiens. Ion concentrations were determined in thin freeze-dried cryosections using energy-dispersive X-ray microanalysis. Metabolic inhibition was compared to direct inhibition of the Na pump by ouabain. At similar rates of transepithelial Na transport, inhibition of the Na pump always resulted in much more pronounced Na concentration increase than metabolic inhibition. This result suggests that the apical Na influx is under effective metabolic control. Downregulation of the Na influx during impaired cellular energy metabolism may be a means by which transporting epithelial cells avoid potentially damaging derangements of the intracellular ion composition.

Animals↗

PubMed1989

Cl transport across the basolateral membrane of principal cells in frog skin.

Measurements of cellular electrolyte concentrations were performed using electron microprobe analysis to further characterize the Cl transport across the basolateral membranes of principal cells. Cellular Cl loss into a Cl-free serosal solution can be prevented by combined application of the Cl channel blocker diphenylamine-2-carboxylate and the cotransport inhibitor bumetanide, indicating a cellular Cl exit across a cotransport system. Recovery of the cellular Cl concentration after Cl depletion requires the simultaneous serosal presence of Na, K and Cl. Cellular Rb uptake measurements indicate that Rb instead of K is accepted by the cotransporter. Whereas after Cl depletion more Rb than Cl is taken up into the cells by the cotransporter, almost no Rb enters the cells via this transporter under control conditions. The data suggest that the high cellular Cl concentration is maintained by a Na-K-2Cl cotransporter which during cellular Cl reuptake seems to work like a shuttle but is almost completely silent under control conditions.

Animals↗

PubMed1988

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-Ringer's 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 Ringer's solutions were present on the apical side. With Na-sulfate Ringer's 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-Ringer's 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.

Animals↗

PubMed1988

Na transport stimulation by novobiocin: intracellular ion concentrations and membrane potential.

Microelectrodes and electron microprobe analysis were employed to study the effect of novobiocin on membrane potential and intracellular electrolyte concentrations in the frog skin epithelium. In both species investigated (Rana esculenta and Rana temporaria), novobiocin (1 mM, outer bath) caused a stimulation of transepithelial Na transport, a depolarization of apical membrane potential, a fall in the apical fractional resistance, and an increase in the intracellular Na concentration. The rise in the Na concentration was accompanied by an equivalent fall in the K concentration. All effects of novobiocin were fully reversible by subsequent application of amiloride. The depolarization as well as the Na increase suggests that the natriferic effect of novobiocin is due to a stimulation of the apical Na influx. Combining both measurements it was possible to calculate the effect of novobiocin on the Na permeability of the apical membrane directly. In Rana esculenta novobiocin increased the permeability from 4.5 to 23.2 nm/s. In Rana temporaria the increase was significantly smaller, from 8.7 to 16.9 nm/s. The transport rate as measured by the short-circuit current showed a non-linear dependence on the apical Na permeability. In the range of transport rates normally encountered, however, the current was a linear function of the Na permeability consistent with the view that the apical membrane is rate-limiting in transepithelial Na transport.

Amiloride↗

PubMed1988

Uptake of Br in mitochondria-rich and principal cells of toad skin epithelium.

To elucidate the route of transepithelial Cl transport across amphibian skins, electrolyte concentrations and uptake of Br in different epithelial cell types of toad skin were determined using electron microprobe analysis. Under short-circuited conditions, Cl concentrations were about 10 mmol/kg ww lower in MR-cells (23.9 +/- 9.6 mmol/kg ww) than in principal cells and showed a large scatter. After unilateral substitution of Br for Cl in the bathing solutions, principal cells exchanged Br for Cl only from the serosal side, whereas variable amounts of Br were gained in MR-cells from either side. The ratio of Br to Cl concentrations in MR-cells averaged 0.35 and 0.81 after incubation with NaBr-Ringer's on the apical or serosal side, respectively. After activation of transepithelial anion conductance by serosa-positive voltage-clamping to 100 mV, uptake of Br from the apical side was increased in MR-cells compared with short-circuited conditions. On the average, the ratio of cellular Br to Cl concentrations was 1.38, but the variation among individual MR-cells from the same tissue was considerable. In MR-cells with large uptake of Br and voltage-activated conditions, the sum of Br and Cl concentrations was higher than the Cl concentration under control conditions. The increase of anion content was associated by increase of the Na and corresponding decrease of the K concentrations. The MR-cells were swollen as indicated by the decrease in the cellular dry weight content from 22.2 +/- 2.5 to 17.1 +/- 4.2 g/100 g.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

Na transport stimulation by novobiocin: transepithelial parameters and evaluation of ENa.

The action of the antibiotic novobiocin on transepithelial Na transport was studied in isolated skins obtained from two different frog species. In Rana esculenta addition of novobiocin to the outer bath (1 mM) resulted in a sustained and reversible stimulation of the short-circuit current, transepithelial potential, and transepithelial conductance. Similar, though more variable and much less pronounced changes were observed in Rana temporaria. In the presence of amiloride (0.1 mM) novobiocin had no effect on any of the investigated transport parameters and all novobiocin induced changes were fully reversed when amiloride was given subsequently. At reduced external Na concentration or low pH the action of novobiocin was found to be greatly attenuated. In the presence of novobiocin an increased affinity to amiloride and a linearization of the transepithelial current-voltage relationship was observed. The results are consistent with the view that novobiocin increases the Na permeability of the outer membrane, possibly by an attenuation of an Na self-inhibition mechanism. In addition, the driving force of transepithelial Na transport was estimated by means of novobiocin. Several different methods were employed, providing varying results. As shown in an Appendix, for the most part the discrepancies can be explained by changes in the intracellular Na and K concentration. In some cases, novobiocin induced large secondary increases in the skin conductance which can be referred to an increased Cl permeability.

Amiloride↗

PubMed1988

The distribution of potassium, sodium and chloride across the apical membrane of renal tubular cells: effect of acute metabolic alkalosis.

Studies were undertaken to define the effect of acute metabolic alkalosis (hypertonic sodium bicarbonate i.v.) on the chemical gradients for potassium, sodium and chloride across the apical membrane of individual renal tubule cells. Electron microprobe analysis was used on freeze-dried cryosections of the rat renal cortex to measure electrolyte concentrations in proximal tubule cells and in the various cell types of the superficial distal tubule. Analyses were also performed in fluid samples obtained by micropuncture from proximal and early and late distal collection sites. Compared with the appropriate controls (hypertonic sodium chloride i.v.), administration of sodium bicarbonate resulted only in small and mostly insignificant increases in cell potassium concentrations and induced only minor alterations in the cell/tubule fluid potassium concentration gradient for all cell types analysed. This observation suggests that under this condition factors other than an increase in cell potassium concentration are important in modulating potassium transfer across the apical membrane of potassium secreting cells. Nevertheless, since in alkalosis phosphorus and cell dry weight were decreased, and hence cell volume increased, in all but the intercalated cells, actually the potassium content of most tubular cells was higher under this condition. In comparison with animals infused with isotonic saline at low rates (hydropenic controls), infusion of either hypertonic sodium chloride or sodium bicarbonate led to a sharp increase in distal tubule fluid sodium concentrations and in the sodium concentrations of distal convoluted tubule, connecting tubule and principal cells, indicating that under both conditions the primary event causing enhanced transepithelial sodium absorption is stimulation of the sodium entry step.(ABSTRACT TRUNCATED AT 250 WORDS)

Alkalosis↗

PubMed1988

Differential effects of aldosterone and ADH on intracellular electrolytes in the toad urinary bladder epithelium.

Quantitative electron microprobe analysis was employed to compare the effects of aldosterone and ADH on the intracellular electrolyte concentrations in the toad urinary bladder epithelium. The measurements were performed on thin freeze-dried cryosections utilizing energy dispersive x-ray microanalysis. After aldosterone, a statistically significant increase in the intracellular Na concentration was detectable in 8 out of 9 experiments. The mean Na concentration of granular cells increased from 8.9 +/- 1.3 to 13.2 +/- 2.2 mmol/kg wet wt. A significantly larger Na increase was observed after an equivalent stimulation of transepithelial Na transport by ADH. On average, the Na concentration in granular cells increased from 12.0 +/- 2.3 to 31.4 +/- 9.3 mmol/kg wet wt (5 experiments). We conclude from these results that aldosterone, in addition to its stimulatory effect on the apical Na influx, also exerts a stimulatory effect on the Na pump. Based on a significant reduction in the Cl concentration of granular cells, we discuss the possibility that the stimulation of the pump is mediated by an aldosterone-induced alkalinization. Similar though less pronounced concentration changes were observed in basal cells, suggesting that this cell type also participates in transepithelial Na transport. Measurements in mitochondria-rich cells provided no consistent results.

Aldosterone↗

PubMed1988

Effect of acute metabolic acidosis on transmembrane electrolyte gradients in individual renal tubule cells.

We studied the effect of acute metabolic acidosis on potassium, sodium and chloride gradients across the apical membrane of proximal and distal tubule cells by determining electrolyte concentrations in individual cells and in tubule fluid employing electron microprobe analysis. Cellular measurements were performed on freeze-dried cryosections of the renal cortex, analysis of tubule fluid electrolyte concentrations on freeze-dried microdroplets of micropuncture samples obtained from proximal and from early and late distal collection sites. Acidosis (NH4Cl i.v. and i.g.) induced a substantial rise in plasma potassium concentration without significant effects on cell potassium concentrations. Potassium concentrations along the surface distal tubule were also unaltered; thus the chemical driving force for potassium exit from cell to lumen was not affected by acidosis. In all but intercalated cells acidosis markedly increased cell phosphorus concentration and cell dry weight indicating cell shrinkage and thus diminution of cell potassium content. Because the increase in intracellular chloride concentration exceeded the increase in plasma chloride concentration, the chemical chloride gradient across the contraluminal membrane was markedly depressed by acidosis.

Acidosis↗