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R Rick

Publications and source records attributed to R Rick.

At least 37 records · Page 2Linked to original sources
PubMed1987

Effect of potassium adaptation on the distribution of potassium, sodium and chloride across the apical membrane of renal tubular cells.

To assess the effect of K adaptation on the electrolyte concentrations of renal tubular cells and on the concentration gradients across the luminal membrane, electron microprobe analysis was employed on freeze-dried cryosections of the renal cortex and on freeze-dried samples of tubular fluid in control and high-K rats. The measurements were performed in individual cells of the proximal and superficial distal tubule and on samples of tubular fluid obtained by free flow micropuncture from proximal and early and late distal collection sites. The ingestion of a potassium-rich diet for at least 10 days together with an acute potassium load of 0.4 mmol/kg/h led to a small increase in potassium concentration of about 7 mmol/kg wet weight (w.w.) in all cell types analysed. In distal convoluted tubule, connecting tubule and principal cells sodium concentration was markedly decreased by 4, 4, and 6 mmol/kg w.w., respectively, while no significant changes in sodium concentration were found in proximal tubule and intercalated cells. No consistent changes in cell chloride could be observed under K adaptation. Analysis of the tubular fluid samples showed that the K concentration gradient across the apical cell membrane of all distal tubular cell types investigated was diminished in the high-K rats. The concentration gradient for sodium entry, however, was clearly enhanced in the distal convoluted tubule, connecting tubule and principal cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Intracellular solute gradients during osmotic water flow: an electron-microprobe analysis.

In an attempt to quantify possible intracellular water activity gradients during ADH-induced osmotic water flow, we employed energy dispersive X-ray microanalysis to thin, freeze-dried cryosections obtained from fresh, shock-frozen tissue of the toad urinary bladder. The sum of all detectable small ions (Na + K + Cl) in the cellular water space was taken as an index of the intracellular osmolarity. Presuming that all ions are osmotically active, they comprise about 90% of the cellular solutes. When the cells were exposed to dilute serosal medium, the reduction in the sum of the ions agreed well with the expected reduction in osmolarity. After inducing water flow by addition of ADH and dilution of the mucosal medium, all epithelial cells showed a fall in osmolarity. The change was more pronounced in granular cells than in basal or mitochondria-rich cells, consistent with the notion that granular cells represent the main transport pathway. Most significantly, intracellular osmolarity gradients, largely caused by an uneven distribution of K and Na, were detectable in granular cells. The gradients were not observed after ADH or mucosal dilution alone, or when the direction of transepithelial water flow was reversed. We conclude from these results that there is a significant cytoplasmic resistance to water flow which may lead to intracellular gradients of water activity. Concentration gradients of diffusible cations can be explained by a flow-induced Donnan-type distribution of fixed negative charges. With regard to transepithelial Na transport, the data suggest that ADH stimulates transport by increasing the Na permeability of the apical membranes of granular cells specifically.

Animals↗
PubMed1987

Intracellular ion concentrations in the frog cornea epithelium during stimulation and inhibition of Cl secretion.

The intracellular electrolyte concentrations in the isolated cornea of the American bullfrog were determined in thin freeze-dried cryosections using energy-dispersive X-ray microanalysis. Stimulation of Cl secretion by isoproterenol resulted in a significant increase in the intracellular Na concentration but did not change the intracellular Cl concentration. Similar results were obtained when Cl secretion was stimulated by the Ca ionophore A23187. Inhibition of Cl secretion by ouabain produced a large increase in the intracellular Na concentration and an equivalent fall in the K concentration. Again, no increase or decrease in the intracellular Cl concentration was detectable. Clamping of the transepithelial potential to +/- 50 mV resulted in parallel changes in the transepithelial current and intracellular Na concentration, but, with the exception of the outermost cell layer, in no changes of the Cl concentration. Only when Cl secretion was inhibited by bumetanide or furosemide, together with a decrease in the Na concentration, was a large fall in the Cl concentration observed. Application of loop diuretics also produced significant increases in the P concentration and dry weight, consistent with some shrinkage of the epithelial cells. The results suggest the existence of a potent regulatory mechanism which maintains a constant intracellular Cl concentration and, thereby, a constant epithelial cell volume. Through the operation of this system any variation in the apical Cl efflux is compensated for by an equal change in the rate of Cl uptake across the basolateral membrane. Cl uptake is sensitive to loop diuretics, directly coupled to an uptake of Na, and dependent on the Na and K concentration gradients across the basolateral membrane. Isoproterenol and A23187 seem to increase the Cl permeability of the apical membrane and thus stimulate Cl efflux. Ouabain inhibits Cl secretion by abolishing the driving Na concentration gradient for Cl uptake across the basolateral membrane.

Animals↗
PubMed1985

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.

Animals↗
PubMed1985

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 osmolalities. In antidiuresis and diuresis the sum of intracellular cations (sodium and potassium), accompanying anions and urea was insufficient in both cases to provide cell osmolalities 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.

Animals↗
PubMed1985

Electron microprobe analysis of proximal tubule cellular Na, Cl and K element concentrations during acute mannitol-saline volume expansion in rats: evidence for inhibition of the Na pump.

It has previously been shown that during mannitol-saline volume expansion (VE) Na transport was inhibited 50% by harvested proximal tubular fluid without a change in paracellular shunt pathway permeability to Na. To determine whether this inhibition was due to changes in cellular entry step or an effect on the pump itself, intracellular element concentrations were measured by electron microprobe X-ray ranalysis in proximal tubular cells of control (non-expanded, NE) and VE rats. Nai, Cli and phosphorusi were increased (mean +/- S.E.) from 19.3 +/- 0.8 to 23.4 +/- 0.6, 15.8 +/- 0.4 to 21.3 +/- 0.4 and 124.3 +/- 2.6 to 138.0 +/- 1.8 mmol . kg-1 wet weight (P less than 0.001) respectively while Ki remained unchanged: 122.9 +/- 2.2 and 124.2 +/- 1.3 mmol . kg-1 wet weight. The increases in Nai and Cli were in excess of cell shrinkage produced by the hyperosmolal peritubular environment while the unchanged Ki in the face of cell shrinkage indicates and actual loss. It is concluded that mannitol-saline VE inhibits the Na pump producing a rise in Nai and a fall in Ki.

Animals↗
PubMed1985

Cl transport in the frog cornea: an electron-microprobe analysis.

The intracellular electrolyte concentrations of the bullfrog corneal epithelium have been determined in thin freeze-dried cryosections using the technique of electron-microprobe analysis. Under control conditions, transepithelial potential short-circuited and either side of the cornea incubated in Conway's solution, the mean intracellular concentrations (in mmol/kg wet weight) were 8.0 for Na, 18.4 for Cl and 117.3 for K. These values are in good agreement with ion activities previously obtained by Reuss et al. (Am. J. Physiol. 244:C336-C347, 1983) under open-circuit conditions. From a comparison of the chemical concentrations and activities of Na and K a mean intracellular activity coefficient of 0.75 is calculated. For small ions no significant differences between nuclear and cytoplasmic concentration values were detectable. The Cl concentrations in the different epithelial layers were virtually identical and showed parallel changes at varying states of Cl secretion, suggesting that the epithelium represents a functional syncytium. For Na a concentration gradient between the outer and inner epithelial layer was observed, which can be accounted for by two different models of epithelial cooperation. The behavior of the intracellular Na and Cl concentrations after removal of Na, Cl or K from the outer or inner bathing medium provides support for a passive electrodiffusive Cl efflux across the apical membrane and a Na-coupled Cl uptake across the basolateral membrane. The results are inconclusive with regard to the exact mechanism of Cl uptake, indicating either a variable stoichiometry of the symporter or the presence of more than one transport system. Furthermore, a dependence of intracellular Cl on HCO3 and CO2 was observed. Extracellular measurements in corneal stroma demonstrated that ion concentrations in this space are in free equilibrium with the inner bath.

Animals↗
PubMed1985

Electron microprobe analysis of intracellular electrolytes in resting and isoproterenol-stimulated exocrine glands of frog skin.

In the intact, in vitro frog skin, isoproterenol (ISO) stimulates an amiloride-insensitive increase in short-circuit current (SCC) that can be localized to the exocrine glands and is associated with secretion of chloride. To determine which cells in the glands respond to stimulation we measured the intracellular electrolyte concentrations of the various cell types of the mucous and seromucous glands of the skin using freeze-dried cryosections and electron microprobe analysis. In the resting state, the various cell types of the glands have intracellular electrolyte concentrations similar to the epithelial cells of the skin. Exposure to amiloride (10(-4) M) has little effect on the concentration of Na and Cl in the cells of the glands. The effect of isoproterenol has two distinct phases. Analysis of glands in tissues frozen at the peak of the SCC response (13 min after addition of isoproterenol) shows that the only significant change is an increase in Na and Ca in a group of cells at the ductal pole of the acini of both gland types. These are termed "gland" cells. The duct cells and cells that secrete macromolecules did not show any significant changes at this timepoint. In the gland cells, after a one-hour exposure to isoproterenol the Na concentration is at prestimulation levels while Cl drops. There is also a smaller drop in Cl in the duct and skin epithelial cells. Ouabain, which can completely block the isoproterenol SCC response, has little short-term effect on Na and Cl in the control gland but accentuates the gain of Na and drop in Cl in the isoproterenol-treated condition. Bumetanide and, to a lesser extent, furosemide, also blocks the isoproterenol SCC response and causes a further drop in Cl. The results provide indirect evidence that a major portion of the ionic component of the gland secretion is produced by a distinct group of cells separate from those producing the macromolecular component and that the mechanism of secretion involves a Na: Cl coupled transport system linked to the activity of the basolateral Na pump.

Amiloride↗
PubMed1985

Electron microprobe analysis of chloride secretion in the frog cornea.

Electron microprobe analysis was employed to measure the intracellular electrolyte concentrations of the bullfrog corneal epithelium. Under control conditions, transepithelial potential short-circuited and both sides of the isolated cornea incubated in Conway's solution, the mean intracellular concentrations were 8.0 for sodium, 18.4 for chloride and 117.3 for potassium (mmole/kg wet weight). These values are in good agreement with previously reported ion activities implying that the intracellular activity co-efficient for small ions is close to that of the extracellular space. No significant differences between the nuclear and cytoplasmic concentrations of small diffusible ions were detectable. Similarly, the chloride concentrations in the different epithelial layers were virtually identical and showed parallel changes at varying states of chloride secretion, suggesting that corneal epithelium represents a functional syncytium. The behavior of the intracellular ion concentrations after removal of sodium, chloride or potassium from the outer or inner bath is consistent with a passive electrodiffusive efflux of chloride across the outer membrane and a sodium coupled chloride uptake across the inner membrane. Furthermore, effects of bicarbonate and CO2 on the rate of chloride secretion and on the intracellular sodium and chloride concentrations were observed, indicating a possible role of pH in regulating chloride secretion.

Animals↗
PubMed1984

Intracellular electrolyte concentrations in rat sympathetic neurones measured with an electron microprobe.

Intracellular element concentrations were measured in rat sympathetic neurones using energy dispersive electron microprobe analysis. The resting intracellular concentrations of sodium potassium and chloride measured in ganglia maintained for about 90 min in vitro at 25 degrees C were 3, 155 and 25 mmol/kg total tissue wet weight respectively. Recalculated in mmol/l cell water, these values are 5, 196 and 32 respectively. There were no significant differences between the nuclear and cytoplasmic values of these ions. Incubation in either carbachol (180 mumol/l, 4 min) or ouabain (1 mmol/1, 60 min) significantly increased the intracellular sodium and decreased the intracellular potassium concentrations. Neither substance materially altered the intracellular chloride concentration. The data obtained are compared and contrasted to those obtained in mammalian sympathetic neurones using chemical analysis and ion-sensitive microelectrodes.

Animals↗
PubMed1984

Intracellular electrolyte concentrations in the frog skin epithelium: effect of vasopressin and dependence on the Na concentration in the bathing media.

The intracellular electrolyte concentrations of the frog skin epithelium have been determined in thin freeze-dried cryosections using the technique of electron microprobe analysis. Stimulation of the transepithelial Na transport by arginine vasopressin (AVP) resulted in a marked increase in the Na concentration and a reciprocal drop in the K concentration in all epithelial cell layers. The effects of AVP were cancelled by addition of amiloride. It is concluded from these results that the primary mechanism by which AVP stimulates transepithelial Na transport is an increase in the Na permeability of the apical membrane. However, also some evidence has been obtained for an additional stimulatory effect of AVP on the Na pump. In mitochondria-rich cells and in gland cells no significant concentration changes were detected, supporting the view that these cells do not share in transepithelial Na transport. Furthermore, the dependence of the intracellular electrolyte concentrations upon the Na concentration in the outer and inner bathing solution was evaluated. Both in control and AVP-stimulated skins the intracellular Na concentration showed saturation already at low external Na concentrations, indicating that the self-inhibition of transepithelial Na transport is due to a reduction of the permeability of the apical membrane. After lowering the Na concentration in the internal bath frequently a Na increase in the outermost and a drop in the deeper epithelial layers was observed. It is concluded that partial uncoupling of the transport syncytium occurs, which may explain the inhibition of the transepithelial Na transport and blunting of the AVP response under this condition.

Amiloride↗
PubMed1984

Intra- and extracellular element concentrations of rat renal papilla in antidiuresis.

The element concentrations in various intra- and extracellular compartments of the tip of the rat renal papilla were determined during antidiuresis using electron microprobe analysis. Urinary concentrations (means +/- SEM) were: urea, 1509 +/- 116; potassium, 268 +/- 32; sodium, 62 +/- 19 mmoles X 1(-1); and osmolality, 2548 +/- 141 mOsm X kg-1. Electrolyte concentrations in the interstitial space were: sodium, 437 +/- 19; chloride, 438 +/- 20; and potassium, 35 +/- 2 mmoles X kg-1 wet wt. The vasa recta plasma exhibited almost identical element concentrations. The values in the papillary collecting duct cells were: sodium, 28 +/- 1; chloride, 76 +/- 3; potassium, 135 +/- 3; and phosphorus, 316 +/- 7 mmoles X kg-1 wet wt. Similar concentrations were observed in the papillary epithelial cells. In interstitial cells potassium and phosphorus concentrations were virtually identical to those of the collecting duct cells, whereas sodium and chloride concentrations were higher by about 30 mmoles X kg-1 wet wt. The element composition of the various papillary cells is, thus, not substantially different from that of proximal tubular cells. This finding demonstrates that cellular accumulation of electrolytes is not the regulatory mechanism by which papillary cells adapt osmotically to their high environmental osmolality and sodium chloride concentration.

Adaptation, Physiological↗
PubMed1984

Intracellular electrolyte composition in various experimental models of hypertension: an electron microprobe study.

Changes in the intracellular ionic composition in the three models of hypertension studied are not uniform in the cells of the various organs. The composition differs not only from organ to organ, but even among the various cell types within the same organ. Marked differences--even diametrically opposite changes--in the intracellular Na concentration can be detected in the various models of hypertension studied. Hence, one cannot expect to draw a simple unifying hypothesis from an analysis of the changes in intracellular electrolyte concentrations occurring in hypertension. A more quantitative analysis of the intracellular ionic composition in other cells, particularly in vascular cells, is needed to define the characteristics of the various types of hypertension.

Animals↗
PubMed1983

Sodium and potassium concentrations of renal cortical cells two animal models of primary arterial hypertension.

Electron microprobe analysis was used to determine cellular concentrations of potassium and sodium in renal cortical cells of hypertensive rats of the Milan strain (MHS) and spontaneously hypertensive rats of the stroke prone strain (SHRSP) and their respective controls. Potassium concentrations in proximal and distal tubular cells were similar in both strains of hypertensive rats compared with their normotensive controls. In MHS rats proximal tubular cell sodium concentration was lower than in controls by 3.1 mmol/kg ww, whereas in both proximal and distal tubular cells of SHRSP sodium concentrations were higher than in controls by 5.3 and 4.3 mmol/kg ww, respectively. These results indicate that changes in the transport characteristics of the renal tubular epithelium are a feature of both models of hypertension.

Animals↗
PubMed1983

Analysis of epithelial ion transport by X-ray microanalysis.

Energy dispersive X-ray microanalysis was employed to determine the intracellular electrolyte concentrations in various epithelial tissues. Analyses of the changes in the intracellular electrolyte concentrations during different functional states provided new insights into the mechanisms involved in transepithelial ion transport. Results obtained on the Na transporting frog skin epithelium confirmed the two-barrier concept of transepithelial Na transport involving a passive Na uptake and an active Na extrusion. The Na transport compartment comprises all living epithelial cell layers, only the outer cornified cells, the mitochondria-rich cells and gland cells being exceptions. Na influx across the outer barrier can be inhibited by amiloride or stimulated by novobiocin or vasopressin. In the Cl-secreting frog cornea the electrolyte concentrations in the various epithelial cell layers and cell types were almost identical, indicating that the epithelium forms a functional syncytium with regard to ion transport. Under virtually all experimental conditions the Cl concentration was found to be higher than the expected equilibrium values, favouring a passive exit from the cells towards the tear side. The results are consistent with the existence of a furosemide-sensitive coupled NaCl uptake process at the inner-facing cell membranes. In the rat kidney after K depletion a fall in cellular K by about 20% was observed both in proximal and distal tubular cells. Simultaneously a rise in the intracellular Na concentration was detected which, however, was insufficient to balance the loss in K. No significant differences could be detected between the various epithelial cell types which are thought to be involved in either K reabsorption or secretion. It is concluded that the fall in cellular K is not sufficient to explain the marked reduction in urinary K excretion during K depletion.

Animals↗
PubMed1982

Element concentrations of renal and hepatic cells under potassium depletion.

The effect of dietary potassium depletion on nuclear and cytoplasmic element concentrations in cortical renal tubular cells and hepatocytes was investigated using electron microprobe analysis. Significant differences in sodium and potassium concentrations between nucleus and cytoplasm were not detected either under control or under potassium-depleted conditions. Potassium depletion for at least 14 days resulted in a decrease in plasma potassium concentration from 4.4 +/- 0.1 to 2.0 +/- 0.1 mmoles X liter-1. There was a fall in cellular potassium from 151.6 +/- 3.5 to 120.2 +/- 2.1 in distal tubular cells, from 150.1 +/- 2.6 to 117.7 +/- 1.2 in proximal tubular cells, and from 140.6 +/- 1.3 to 128.0 +/- 1.3 mmoles X kg-1 of wet wt in hepatocytes. The cellular chlorine concentrations fell from 19.9 +/- 0.7 to 15.8 +/- 0.3 and from 21.3 +/- 0.4 to 17.2 +/- 0.4 in proximal tubular and liver cells, respectively, but remained unchanged at 11.4 +/- 0.7 and 11.0 +/- 0.4 mmoles X kg-1 of wet wt in distal tubular cells. The intracellular sodium concentrations rose from 10.4 +/- 0.7 to 15.8 +/- 0.8, 19.1 +/- 0.8 to 24.1 +/- 0.7 and 14.1 +/- 0.5 to 16.2 +/- 0.6 mmoles X kg-1 of wet wt in distal tubular, proximal tubular and liver cells, respectively. This rise in cellular sodium was insufficient in any cell type to compensate for the loss of potassium. No significant differences were found in the cellular electrolyte concentrations of the various distal tubular cell types which are thought to be involved in either potassium reabsorption or secretion. The decrease in potassium concentrations in distal tubular cells by about 20% does not seem sufficient to explain the marked fall in urinary potassium excretion.

Animals↗
PubMed1982

Quantitative analysis of electrolytes in frozen dried sections.

During recent years our group has employed the technique of electron microprobe analysis to determine the electrolyte concentrations in various epithelial tissues. The specimen preparation is characterized by shock-freezing of small tissue pieces in liquid propane/isopentane mixtures at 77 K, cryosectioning of 1 micrometer thick serial sections at 170 K and subsequent freeze-drying at 190 K and 10-4 Pa. The analysis of the frozen dried cryosections is performed in a scanning electron microscopy which is equipped with an energy dispersive X-ray detector. The measuring conditions selected are 17-20 kV acceleration voltage and 0.1-0.5 nA probe current. For quantification, the cellular X-ray spectra are compared with those of an internal albumin standard layer. The evaluation of the characteristic X-ray intensities is performed using a computer program. Some critical points of this technique will be discussed.

Animals↗