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)

Electrolyte composition of renal tubular cells in gentamicin nephrotoxicity

The effect of long-term gentamicin administration on sodium, potassium, chloride and phosphorus concentrations was studied in individual rat renal tubular cells using electron microprobe analysis. Histological damage was apparent only in proximal tubular cells. The extent of damage was only mild after 7 days of gentamicin administration (60 mg/kg body wt/day) but much more pronounced after 10 days. GFR showed a progressive decline during gentamicin treatment. In non-necrotic proximal tubular cells, sodium was increased from 14.6 +/- 0.3 (mean +/- SEM) in controls to 20.6 +/- 0.4 after 7 and 22.0 +/- 0.8 mmol/kg wet wt after 10 days of gentamicin administration. Chloride concentration was higher only after 10 days (20.6 +/- 0.6 vs. 17.3 +/- 0.2 mmol/kg wet wt). Both cell potassium and phosphorus concentrations were diminished by 6 and 15, and by 8 and 25 mmol/kg wet wt after 7 and 10 days of treatment, respectively. In contrast, no major alterations in distal tubular cell electrolyte concentrations could be observed after either 7 or 10 days of gentamicin administration. As in proximal tubular cells, distal tubular cell phosphorus concentrations were, however, lowered by gentamicin treatment. These results clearly indicate that gentamicin exerts its main effect on proximal tubular cells. Decreased potassium and increased sodium and chloride concentrations were observed in proximal tubular cells exhibiting only mild histological damage prior to the onset of advanced tissue injury. Necrotic cells, on the other hand, showed widely variable intracellular electrolyte concentration patterns.

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.

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.

Cellular osmoregulation in renal medulla

Cells of the renal medulla adapt osmotically to varying external electrolyte concentrations mainly by changing the intracellular content of small organic osmoeffectors (osmolytes) such as sorbitol, inositol and trimethylamines. This implies that despite extreme variations in extracellular tonicity the intracellular concentrations of monovalent electrolytes are stabilized at levels optimal for enzyme function and cell metabolism. In contrast to inorganic electrolytes these organic osmolytes are metabolically neutral and thus do not affect cell metabolism. In addition, some of these organic osmoeffectors, the trimethylamine compounds, are known to counteract the deleterious effects of high urea concentrations (prevailing in antidiuresis) on structure and function of cell proteins.

Cell rubidium uptake: a method for studying functional heterogeneity in the nephron

Rubidium uptake into individual tubule cells of rat renal cortex as measured by energy-dispersive X-ray microanalysis on freeze dried cryosections was used as an index of potassium transport. Over a 30 second period following intravenous infusion of rubidium (0.5 mmol/kg body wt) rubidium content increased in all cells. After 30 seconds, rubidium contents were (in mmol/kg dry wt): 225 +/- 8 in distal convoluted tubule cells, 156 +/- 7 in connecting tubule cells, 110 +/- 7 in principal cells, 86 +/- 4 in proximal tubule cells and 24 +/- 2 in intercalated cells (mean +/- SEM). When distal sodium and potassium transport were stimulated by hypertonic saline loading, rubidium uptake was selectively increased into distal convoluted tubule cells by 38%, into connecting tubule cells by 36%, and into principal cells by 52%. However, rubidium uptake into proximal tubule and into intercalated cells remained unchanged. The preferential uptake of rubidium into distal convoluted tubule cells, connecting tubule cells, and principal cells correlates well with the known transport functions of sodium and potassium, whereas intercalated cells are distinguished by low sodium and potassium transport activity.

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)

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.

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.

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.

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)

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Intracellular electrolyte composition following renal ischemia

The technique of electron microprobe analysis was used to determine the intracellular electrolyte concentrations in proximal or distal tubular cells of the rat kidney during ischemia. When the exposed kidney was maintained in air during ischemia, the composition of the surface cells differed little from control, and the electrolyte disturbances were confined to the deeper lying cells. When maintained in nitrogen, all cells underwent changes in cellular electrolyte concentrations that were uniform, indicating that the surface cells can preserve their composition during ischemia by utilizing oxygen from the air. In the proximal tubular cells, after 20 or 60 min of ischemia in nitrogen, sodium increased from 20 to 93 or 112, chloride rose from 21 to 53 or 66, potassium fell from 141 to 65 or 42, phosphate decreased from 145 to 110 or 95 mmoles.kg-1 of wet wt, and the dry wt dropped from 22.6 to 20.3 or 17.5% of wet wt, respectively. In the distal tubular cells, 20 min of ischemia in nitrogen produced little effect on cellular composition, but after 60 min, sodium increased from 11 to 77, chloride rose from 15 to 48, potassium fell from 134 to 89, phosphate decreased from 168 to 145 mmoles.kg-1 of wet wt, and the dry wt dropped from 20.8 to 18.4% of wet wt. The disturbances in sodium and potassium are caused primarily by an inhibition of the sodium/potassium pump, whereas the changes in chloride, phosphate, and dry weight content result mainly from an influx of extracellular fluid. When blood flow was reintroducing, the electrolyte disturbances were rapidly reversed in all cells, restoration being virtually complete within 60 min, but returned in some proximal cells by 18 hr of reperfusion. Thus, the disturbance in electrolyte composition increases with the duration of ischemia, is less pronounced in the distal than proximal cells and, although initially completely reversible when blood flow is restored, reappeared in the proximal cells 1 days after the initial injury.