Quantitative analysis of electrolytes in frozen dried sections

Technologies for Vitrification Based Cryopreservation

Cryopreservation is a unique and practical method to facilitate extended access to biological materials. Because of this, cryopreservation of cells, tissues, and organs is essential to modern medical science, including cancer cell therapy, tissue engineering, transplantation, reproductive technologies, and bio-banking. Among diverse cryopreservation methods, significant focus has been placed on vitrification due to low cost and reduced protocol time. However, several factors, including the intracellular ice formation that is suppressed in the conventional cryopreservation method, restrict the achievement of this method. To enhance the viability and functionality of biological samples after storage, a large number of cryoprotocols and cryodevices have been developed and studied. Recently, new technologies have been investigated by considering the physical and thermodynamic aspects of cryopreservation in heat and mass transfer. In this review, we first present an overview of the physiochemical aspects of freezing in cryopreservation. Secondly, we present and catalog classical and novel approaches that seek to capitalize on these physicochemical effects. We conclude with the perspective that interdisciplinary studies provide pieces of the cryopreservation puzzle to achieve sustainability in the biospecimen supply chain.

Electron microprobe analysis of rabbit ciliary epithelium indicates enhanced secretion posteriorly and enhanced absorption anteriorly

The rate of aqueous humor formation sequentially across the pigmented (PE) and nonpigmented (NPE) ciliary epithelial cell layers may not be uniform over the epithelial surface. Because of the tissue's small size and complex geometry, this possibility cannot be readily tested by conventional techniques. Rabbit iris-ciliary bodies were divided, incubated, quick-frozen, cryosectioned, and freeze-dried for electron probe X-ray microanalysis of the elemental contents of the PE and NPE cells. We confirmed that preincubation with ouabain to block Na(+),K(+)-ATPase increases Na(+) and decreases K(+) contents far more anteriorly than posteriorly. The anterior and posterior regions were the iridial portion of the primary ciliary processes and the pars plicata, respectively. Following interruption of gap junctions with heptanol, ouabain produced smaller changes in anterior PE cells, possibly reflecting higher Na(+) or K(+) permeability of anterior NPE cells. Inhibiting Na(+) entry selectively with amiloride, benzamil, or dimethylamiloride reduced anterior effects of ouabain by approximately 50%. Regional dependence of net secretion was also assessed with hypotonic stress, which stimulates ciliary epithelial cell regulatory volume decrease (RVD) and net Cl(-) secretion. In contrast to ouabain's actions, the RVD was far more marked posteriorly than anteriorly. These results suggest that 1) enhanced Na(+) reabsorption anteriorly, likely through Na(+) channels and Na(+)/H(+) exchange, mediates the regional dependence of ouabain's actions; and 2) secretion may proceed primarily posteriorly, with secondary processing and reabsorption anteriorly. Stimulation of anterior reabsorption might provide a novel strategy for reducing net secretion.

Application of cryofixation and cryoultramicrotomy for biological electron microscopy

Conventional chemical fixation and embedding of specimens in resins are accompanied by many artifacts, including postmortem structural alterations. Antigenicity of constituents of specimens can be deteriorated and soluble elements relocated in the process of chemical fixation and resin-embedding. Cryofixation and cryoultramicrotomy will overcome many of these drawbacks of chemical fixation and resin embedding. The theoretical background, equipment, methods, and applications of cryofixation and cryoultramicrotomy for biological specimens are reviewed.

Recovery of cell volume and electrolytes of A6 cells after re-establishing isotonicity following hypotonic stress

Cellular element concentrations and dry weight contents in A6 cells were determined using electron microprobe analysis to establish whether these cells exhibit a regulatory volume increase (post-RVD-RVI) when re-establishing isotonicity following a hypotonically induced regulatory volume decrease (RVD). Hypotonic stress was induced by reducing basolateral [NaCl], and hence, osmolarity fell from 260 to 140 mosmol/l. The alterations in cell volume after re-establishing isotonicity, calculated from the cellular dry weight changes, indicate within the first 2 min cell shrinkage from 120 to 76% of control, compatible with almost ideal osmometric behaviour of A6 cells, and thereafter a post-RVD-RVI to 94%. The cellular uptake of osmolytes necessary to explain the post-RVD-RVI could be accounted for solely by a gain in cellular K and Cl. The involvement of a Na-K-2Cl cotransporter in most of the KCl uptake seems plausible since basolateral bumetanide blocked KCl uptake and post-RVD-RVI. The net uptake of cations (K uptake of 185.2, Na loss of 8.2 mmol/kg dry wt) during the isotonic period exceeded the Cl uptake by 38.2 mmol/kg dry wt, suggesting the uptake of another anion and/or the alteration of cellular buffer capacity. The relatively low Na concentration maintained during the isotonic period (13.3 vs. 20.4 mmol/kg wet wt under control conditions) might favour electrolyte uptake via the Na-K-2Cl cotransporter.

Structure and function of human sweat glands studied with histochemistry and cytochemistry

The basic structure and the physiological function of human sweat glands were reviewed. Histochemical and cytochemical techniques greatly contributed the elucidation of the ionic mechanism of sweat secretion. X-ray microanalysis using freeze-dried cryosections clarified the level of Na, K, and Cl in each secretory cell of the human sweat gland. Enzyme cytochemistry, immunohistochemistry and autoradiography elucidated the localization of Na,K-ATPase. These data supported the idea that human eccrine sweat is produced by the model of N-K-2Cl cotransport. Cationic colloidal gold localizes anionic sites on histological sections. Human eccrine and apocrine sweat glands showed completely different localization and enzyme sensitivity of anionic sites studied with cationic gold. Human sweat glands have many immunohistochemical markers. Some of them are specific to apocrine sweat glands, although many of them stain both eccrine and apocrine sweat glands. Histochemical techniques, especially immunohistochemistry using a confocal laser scanning microscope and in situ hybridization, will further clarify the relationship of the structure and function in human sweat glands.

Use of a new adhesive film for the preparation of multi-purpose fresh-frozen sections from hard tissues, whole-animals, insects and plants

A method for preparing thin fresh-frozen sections from large samples and hard tissues is described and the applications are shown. A new adhesive film is introduced to produce the frozen sections. The sample is frozen in a cooled hexane or liquid nitrogen, and then freeze-embedded with 4-5% carboxymethyl cellulose (CMC) in the coolant. A specially prepared adhesive film is fastened to the cut surface of the sample in order to support the section and cut slowly with a disposable tungsten carbide blade. The adhesive film is made of a thin plastic film and an adhesive before use. This method produces 2-microm thick fresh-frozen sections from a large sample, bone or tooth. The "film-section" i.e. the section attached to the adhesive film, can be used for many types of studies such as histology, general histochemistry, enzyme histochemistry, immunohistochemistry, in situ hybridization, elemental analysis, and autoradiography for water-soluble materials. Immunohistochemistry and in situ hybridization can be carried out with nonfixed and undecalcified sections. The section on the adhesive film can be transferred to a glass slide and mounted under a cover slip, and stained sections can be examined with an optical microscope at high magnification. This method is also useful for preparing frozen sections from samples of fish, insects, and plants. Furthermore, samples of particular areas can be collected from the film-section by means of a laser microdissection technique. The multiple possible applications of the adhesive film render it highly useful for studies in biological and medico-dental fields.

Formation of the aqueous humor

1. Glaucoma is a worldwide disease affecting approximately 1-2% of the population aged over 35 years in industrial countries and is a major cause of blindness. 2. Glaucoma is usually associated with an increased intraocular pressure reflecting an imbalance between the rate of production of fluid (the aqueous humor) by the ciliary epithelial cells and its drainage from the eye. Therefore, it is important to understand how this secretion is produced. This requires a knowledge of ciliary epithelial cell composition, which has, in the past, proved difficult to obtain in mammalian preparations. 3. We have recently used the technique of electron-probe X-ray microanalysis to determine this composition under a variety of in vitro conditions. 4. Our results have led to a new model for this secretion that emphasizes the potential secretory role of the Na+/K+/2Cl- cotransporter.

Transcellular sodium transport and basolateral rubidium uptake in the isolated perfused cortical collecting duct

The relation between transcellular Na+ absorption, intracellular Na+ concentration and Na+/K(+)-ATPase activity (the last estimated by the rubidium uptake across the basolateral cell membrane) was examined in the different cell types of the rabbit cortical collecting duct (CCD). Experiments were performed on isolated perfused CCD in which Na+ absorption was varied by perfusing the tubule with solutions containing different Na+ concentrations (nominally Na(+)-free, 30 mM and 144 mM). Experiments were terminated by shock-freezing the tubules during perfusion. Precisely 30 s before shock-freezing, the K+ in the bathing solution was exchanged for Rb+. Intracellular element concentrations, including Rb+, were determined in freeze-dried cryosections of the tubules using energy-dispersive X-ray analysis. Increasing Na+ concentration in the perfusion solution caused significant rises in intracellular Na+ concentration and Rb+ uptake of principal cells. Principal cell Na+ and Rb+ concentrations were 7.8 +/- 0.9 and 7.0 +/- 0.8 mmol/kg wet weight respectively, when the perfusion solution was Na(+)-free, 10.1 +/- 0.7 and 11.6 +/- 0.6 mmol/kg wet weight with 30 mM Na+ in the perfusion solution, and 14.5 +/- 1.5 and 14.9 +/- 0.9 mmol/kg wet weight with 144 mM Na+ in the perfusion solution. In contrast, a comparable relationship between lumen Na+ concentration, intracellular Na+ concentration and basolateral Rb+ uptake was not seen in intercalated cells. These results support the notion that principal, but not intercalated, cells are involved in transepithelial Na+ absorption. In addition, the data demonstrate that apical Na+ entry and basolateral Na+/K(+)-ATPase activity are closely coupled in principal cells of the rabbit CCD.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Tubular sodium handling and tubuloglomerular feedback in compensatory renal hypertrophy

Tubular sodium handling and tubuloglomerular feedback (TGF) activity were assessed in established compensatory renal hypertrophy in Sprague Dawley rats. Hyperfiltration at the level of the single nephron was confirmed 4-6 weeks following a reduction in renal mass. TGF activity, determined as the difference between late proximal and early distal measurements of single-nephron glomerular filtration rate (SNGFR), was significantly increased in compensatory renal hypertrophy, being 7.8 +/- 1.0 vs 23.3 +/- 1.9 vs 25.5 +/- 2.6 nl/min (P for analysis of variance less than 0.05) following sham operation, unilateral nephrectomy, and 1 1/3 nephrectomy, respectively. Enhanced net tubular Na transport was also observed, with total Na reabsorption up to the late proximal site being 1.8 +/- 0.2 vs 2.7 +/- 0.1 vs 3.1 +/- 0.3 nmol/min (P less than 0.05), and to the early distal site being 3.4 +/- 0.5 vs 5.8 +/- 0.6 vs 7.9 +/- 0.8 nmol/min (P less than 0.05) in the three animal groups respectively. Comparison of proximal tubular length demonstrated a 71.9 +/- 8.1% increase in uninephrectomised vs sham-operated animals. This increase was proportionately greater than the increase in proximal Na reabsorption (50.0 +/- 4.0%) observed in the corresponding animal groups. Concurrent electron microprobe experiments in uninephrectomised and sham-operated animals demonstrated that the proximal tubular intracellular Na concentration was significantly lower following uninephrectomy (16.8 +/- 0.6 vs 18.9 +/- 0.5 mmol/kg wet weight, P less than 0.01), in association with evidence of reduced basolateral Na/K-ATPase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Suggestions for the quantitative X-ray microanalysis of thin sections of frozen-dried and embedded biological tissues

When a microregion in a thin section of frozen-dried and embedded tissue is analysed by the conventional electron-probe X-ray continuum-normalization method, the measured quantity is in mmol of element per kg of embedded specimen. As each microregion contains an unknown amount of embedding medium, this quantity generally lies indeterminately somewhere within the wide range between mmol of element per kg of hydrated tissue and mmol of element per kg of dehydrated tissue. However, if a 'tag' element is incorporated in the embedding medium, the contribution of the medium to the local continuum count in each probed field should be measureable, and the X-ray data may then unambiguously yield mmol of element per kg of dehydrated tissue. This result should not be affected by shrinkage on freeze-drying or by incomplete replacement of water by embedding medium. The same X-ray data can additionally provide estimates of mmol of element per unit volume, mmol of element per kg of hydrated tissue and local dry-mass fraction. However, these estimates are subject to errors due to tissue shrinkage, incomplete replacement of water and beam damage.

Effects of potassium-free media and ouabain on epithelial cell composition in toad urinary bladder studied with X-ray microanalysis

The technique of X-ray microanalysis was used to study the composition of toad urinary bladder epithelial cells incubated in Na Ringer's and K-free medium, with and without ouabain. Following incubation under short-circuit conditions, portions of tissue were coated with an external albumin standard and plunge-frozen. Cryosections were freeze-dried and analyzed. In Na Ringer's, granular and basal cells, and also the basal portion of the goblet cells, had similar water and ion compositions. In contrast, mitochondria-rich cells contained less Cl and Na. On average, the granular cells and a subpopulation of the basal cells lost K and gained Na after ouabain and in K-free medium alone. However, there was considerable variation from cell to cell in the responses, indicating differences between cells in the availabilities of ion pathways, either as a consequence of differences in the numbers of such pathways or in their control. In contrast, the compositions of both the low Cl, mitochondria-rich cells and a sub-population of the basal cells were little affected by the different incubation conditions. This is consistent with a comparatively low Na permeability of these cells. The results also indicate that (i) much, if not all, of the K in the dominant cell type, the granular cells, is potentially exchangeable with serosal medium Na, and (ii) Na is accumulated from the serosal medium under K-free conditions. They also provide information about the role of the (Na-K)-ATPase in the maintenance of cellular K in K-free medium, being consistent with other evidence that removal of serosal medium K inhibits transepithelial Na transport by decreasing Na entry to the cells from the mucosal medium, rather than solely by inhibiting the basolateral membrane (Na-K)-ATPase.

Electron probe X-ray microanalysis of intracellular element concentrations in cryosections in the presence of changes in cell volume

The interpretation of element concentration data for X-ray microanalyses of biological tissues, which are subjected to some experimental treatment, can be complicated by changes in cell volume and total cell dry matter induced by the treatment. We have examined the manner in which such changes would affect the values measured in frozen-dried cryosections of soft tissues, and how they may be taken into account in the interpretation of the results. The element content (mass per unit dry weight) measured by the peak-to-continuum or Hall method is independent of changes in cell volume, but is sensitive to a change in the local dry mass. Conversely, intracellular concentrations in terms of mass per unit volume, as determined by the peripheral or internal standard technique, are dependent on volume changes but independent of dry mass. The estimated dry weight fraction is affected by changes in both volume and dry mass. The results obtained from both quantification methods can therefore provide information on the combination of changes in cellular element levels, volume and total dry mass that may occur following the experimental treatment. In a study of the late effect of the drug cisplatin on electrolyte concentrations in kidney proximal tubules, both quantification methods have been used to obtain wet weight and dry weight concentrations. By applying the above considerations, the analytical results have been interpreted as a combination of changes in element levels and a shrinkage of the tubule cells. Cell shrinkage was confirmed by morphometric analysis of tubular cross-sections.

Proximal tubular cell sodium concentration in early diabetic nephropathy assessed by electron microprobe analysis

Electron microprobe X-ray analysis techniques were employed in order to assess the changes that occur in proximal tubular cell sodium concentration during the hyperfiltration phase of early diabetes mellitus induced by streptozotocin in Sprague Dawley rats. Intracellular rubidium accumulation following intravenous infusion of rubidium chloride was used as a marker of basolateral Na/K-ATPase activity. The diabetic animals studied had a significantly higher glomerular filtration rate compared with controls [1.44 +/- 0.07 vs. 1.00 +/- 0.07 ml min-1 (100 g body weight)-1; mean +/- SEM, P less than 0.001]. Intracellular Na concentration was significantly higher in diabetic animals (19.5 +/- 0.6 vs. 17.8 +/- 0.4 mmol/kg wet weight; P less than 0.01). Concurrent measurement of Rb demonstrated significantly higher intracellular accumulation in the proximal tubules of diabetic animals compared with control (7.9 +/- 0.5 vs. 5.5 +/- 0.5 mmol/kg wet weight; P less than 0.001). These results indicate that proximal tubular Na/K-ATPase activity is enhanced in the hyperfiltration phase of diabetes mellitus. Since, however, intracellular Na concentration is increased under these conditions, it may be inferred that apical Na entry into proximal tubular cells is stimulated beyond the rate of basal exit during the initial development of hyperfiltration. The reasons for these alterations in cellular Na transport are unclear but similar changes have been implicated in the pathogenesis of cell growth.

The measurement of water distribution in frozen specimens

There are three techniques to measure local water fractions in the cryomicroscope. First, water content may be measured by a direct analysis of oxygen in bulk samples using a windowless detector. Secondly, mass thickness may be estimated in frozen-hydrated, then frozen-dried sections. This technique offers unrivalled spatial resolution, especially if the radiation dose in the frozen-hydrated state is kept low by the use of electron scattering techniques instead of an X-ray microanalytical background determination. External water content standards can be used instead of frozen-hydrated sections and the whole analysis can even be performed exclusively on frozen-dried sections at room temperature. Thirdly, local water fractions can be evaluated from X-ray microanalytical measurements of element concentrations per mass in the frozen-hydrated and frozen-dried state. Corrections necessary for the other techniques cancel out. However, the high radiation dose required for a fully quantitative analysis excludes the use of these methods in thin or ultrathin sections.

Ice crystal damage and radiation effects in relation to microscopy and analysis at low temperatures

There are several limitations to the low-temperature techniques which are currently being used for the preparation, examination and analysis of biological and organic samples by means of high-energy beam instrumentation. The low thermal conductivity of samples and the inadequacy of rapid cooling techniques means that, with the exception of thin-film suspensions and the surface of impact-cooled bulk specimens which may be vitrified, ice crystals of varying sizes will be present in nearly all samples which are quench cooled. Data are presented which indicate the depth to which adequate cryo-fixation may be achieved for both morphological and analytical studies. Although dynamic processes may be time resolved in the outer parts of quench-cooled samples, the decreased freezing rate below the surface makes resolution of these processes much less certain. The quality of information which may be obtained from quench-cooled samples is limited by radiation damage. Low-dose microscopy of vitrified thin-film suspensions of macromolecules continues to provide valid structural information at the molecular level. The increased doses needed for X-ray microanalysis present serious problems with the high spatial resolution analysis of thin frozen-hydrated sections although much less damage is observed in dried samples. A case is presented for using the outer fracture faces of frozen-hydrated bulk samples for low-resolution analysis of cells and tissues.

Disruption of cellular elements and water in neurotoxicity: studies using electron probe X-ray microanalysis

Regulation of elements and water in nerve cells is a complex, multifaceted process which appears to be vulnerable to neurotoxic events. However, much of our knowledge concerning the potential role of elements in nerve cell injury is limited by the relatively gross level of corresponding analyses. If we are to confirm and understand the proposed role, more precise and detailed information is needed. As indicated in this commentary, research employing electron probe microanalysis and digital X-ray imaging has begun to provide this necessary information. Recent EPMA studies of nerve and glial cells in the peripheral and central nervous systems have shown that each cell type and their corresponding morphologic compartments exhibit unique distributions of elements and water. The use of microprobe analysis has allowed us to document precisely how elements and water redistribute in morphological compartments of damaged nerve cells. Accumulating evidence from EPMA studies suggests that, rather than being an epiphenomenon, intracellular changes in diffusible elements might mediate the functional and structural consequences of neurotoxic insult. It is also evident from this research that elements other than Ca might play a pertinent role in the injury response and that changes in intraneuronal elemental composition might develop according to a specific temporal pattern, e.g., transection-induced sequential alterations in axonal K, Na, Cl, and Ca. Therefore, rather than conducting end-point studies, longitudinal investigations are necessary to define the sequential pattern of elemental perturbation associated with a given neurotoxic event. Such research can also help identify the role of individual elements in the injury response. Future microprobe studies should be combined with measurements of ion levels (e.g., using fura-2 or ion selective electrodes) to provide a comprehensive and dynamic view of elemental deregulation. In addition, parallel biochemical studies should be performed to determine mechanisms of elemental disruption and possible biochemical and metabolic consequences of this disruption. Although evidence presented in this commentary suggests that each type of neurotoxic event produces a characteristic pattern of decompartmentalization, further work is necessary to confirm this possibility. Finally, based on a presumed involvement of elements in nerve injury, efforts are currently underway in several laboratories to develop appropriate pharmacological therapies for certain chemical- and trauma-induced neuropathological conditions (Dretchen et al., 1986; El-Fawal et al., 1989; Beattie et al., 1989).(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Calcium measurements with electron probe X-ray and electron energy loss analysis

This paper presents a broad survey of the rationale for electron probe X-ray microanalysis (EPXMA) and the various methods for obtaining qualitative and quantitative information on the distribution and amount of elements, particularly calcium, in cryopreserved cells and tissues. Essential in an introductory consideration of microanalysis in biological cryosections is the physical basis for the instrumentation, fundamentals of X-ray spectrometry, and various analytical modes such as static probing and X-ray imaging. Some common artifacts are beam damage and contamination. Inherent pitfalls of energy dispersive X-ray systems include Si escape peaks, doublets, background, and detector calibration shifts. Quantitative calcium analysis of thin cryosections is carried out in real time using a multiple least squares fitting program on filtered X-ray spectra and normalizing the calcium peak to a portion of the continuum. Recent work includes the development of an X-ray imaging system where quantitative data can be retrieved off-line. The minimum detectable concentration of calcium in biological cryosections is approximately 300 mumole kg dry weight with a spatial resolution of approximately 100 A. The application of electron energy loss (EELS) techniques to the detection of calcium offers the potential for greater sensitivity and spatial resolution in measurement and imaging. Determination of mass thickness with EELS can facilitate accurate calculation of wet weight concentrations from frozen hydrated and freeze-dried specimens. Calcium has multiple effects on cell metabolism, membrane transport and permeability and, thus, on overall cell physiology or pathophysiology. Cells can be rapidly frozen for EPXMA during basal or altered functional conditions to delineate the location and amount of calcium within cells and the changes in location and concentration of cations or anions accompanying calcium redistribution. Recent experiments in our laboratory document that EPXMA in combination with other biochemical and electrophysiological techniques can be used to study, for example, sodium and calcium compartmentation in cultured cardiac cells. Such analyses can also be used to clarify the role of calcium in anoxic renal cell injury and to evaluate proposed ionic defects in cells of individuals with cystic fibrosis.

Standards for the application of X-ray microanalysis to biological specimens

A review on the subject of compounds used as standards for biological X-ray microanalysis is presented. The general approach used for standardization has been to use standards which resemble the specimen closely in composition. Thus, standards based on proteins have been used for analysis of quench-frozen cryosectioned specimens, whereas standards based on embedding resins have been used for resin-embedded material. The properties of, and problems associated with, each type of standard are recognized and have been well documented. The choice and analysis of biological material. Attention is drawn to the fact that the problems associated with any quantification procedure need to be kept in mind when analysis of standards is undertaken.

Acute cisplatin nephrotoxicity in the rat. Evidence for impaired entry of sodium into proximal tubule cells

The earliest phase of cisplatin nephrotoxicity involves natriuresis due to impaired sodium reabsorption by the proximal tubule. To define the cell mechanism of this transport lesion, electron microprobe X-ray analysis was used to determine changes in the electrolyte composition of proximal tubule cells in kidneys taken from rats treated acutely with cisplatin (1 mg/100 g body weight). Compared to control animals injected with vehicle, cisplatin treated rats developed significant natriuresis, the fractional excretion of sodium rising over sevenfold. In kidneys removed 90 min following cisplatin, sodium concentration in proximal tubule cells was reduced by 4.2 mmol/kg wet weight, or 19%, compared to control values. When allowance was made for cell shrinkage in cisplatin-treated kidneys by deriving the cell content of sodium (mmol/kg dry weight), the reduction was even greater (28%). These data suggest that cisplatin reduces proximal tubule sodium reabsorption by inhibiting the entry of sodium into the cells across the apical membrane.

Elemental concentrations in air-exposed and vacuum-stored cryosections of rat liver cells

Elemental concentrations in different compartments of cryosections of isolated rat liver cells cryotransferred and freeze-dried were compared with those obtained after storage under vacuum for 12 or 60 h and after exposure to room air for 2 min. Poorer image contrast and segregation artefacts are frequently found in air-exposed sections, together with a slight but significant decrease of the K concentration in the cytoplasm and an increase of the S concentration in the liver cell nuclei and the extracellular medium. Extreme distortions of both ultrastructure and elemental distributions are observed if the sections are even slightly colder than the surrounding atmosphere. While storage of frozen-dried cryosections under vacuum for less than 12 h does not lead to alterations in the sections, gross changes are found both in morphology and elemental distribution in sections stored under vacuum for about 60 h. Long-time vacuum storage of frozen-dried cryosections is, therefore, not recommended.

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.

Effect of ouabain on electrolyte concentrations in principal and intercalated cells of the isolated perfused cortical collecting duct

Sodium, phosphorus, chloride and potassium concentrations were measured by a new method in individual principal and intercalated cells in the cortical collecting duct in vitro. Electron microprobe analysis was applied to freeze-dried cryosections of the isolated perfused rabbit cortical collecting duct. Cell analyses were performed under control conditions and after addition of ouabain to the bath. Under control conditions similar sodium, potassium, chloride, and phosphorus concentration (means +/- SEM) were observed in principal (10.0 +/- 0.6, 126.5 +/- 2.7, 24.6 +/- 1.0, and 121.5 +/- 3.5 mmol/kg wet weight, respectively) and intercalated cells (9.0 +/- 0.9, 127.1 +/- 4.2, 27.4 +/- 1.8, and 118.7 +/- 4.9 mmol/kg wet weight, respectively). In principal cells ouabain (10 min) caused an increase in sodium and chloride concentrations by 104 and 13 mmol/kg wet weight, and a decrease in potassium and phosphorus concentrations by 106 and 32 mmol/kg wet weight. These changes in cell element concentrations can be ascribed to an exchange of intracellular potassium against extracellular sodium and to cell swelling due to influx of extracellular fluid. The effects of ouabain on intercalated cells were far less pronounced than on principal cells. This different susceptibility to ouabain of principal and intercalated cells can be ascribed to differences in active and passive transmembrane ion transport pathways.

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)

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.

X-ray microanalysis of freeze-dried and frozen-hydrated cryosections

The elemental composition and the ultrastructure of biological cells were studied by scanning transmission electron microscopy (STEM) combined with energy dispersive X-ray microanalysis. The preparation technique involves cryofixation, cryoultramicrotomy, cryotransfer, and freeze-drying of samples. Freeze-dried cryosections 100-nm thick appeared to be appropriate for measuring the distribution of diffusible elements and water in different compartments of the cells. The lateral analytical resolution was less than 50 nm, depending on ice crystal damage and section thickness. The detection limit was in the range of 10 mmol/kg dry weight for all elements with an atomic number higher than 12; for sodium and magnesium the detection limits were about 30 and 20 mmol/kg dry weight, respectively. The darkfield intensity in STEM is linearly related to the mass thickness. Thus, it becomes possible to measure the water content in intracellular compartments by using the darkfield signal of the dry mass remaining after freeze-drying. By combining the X-ray microanalytical data expressed as dry weight concentrations with the measurements of the water content, physiologically more meaningful wet weight concentrations of elements were determined. In comparison to freeze-dried cryosections frozen-hydrated sections showed poor contrast and were very sensitive against radiation damage, resulting in mass loss. The high electron exposure required for recording X-ray spectra made reproducible microanalysis of ultrathin (about 100-nm thick) frozen-hydrated sections impossible. The mass loss could be reduced by carbon coating; however, the improvement achieved thus far is still insufficient for applications in X-ray microanalysis. Therefore, at present only bulk specimens or at least 1-micron thick sections can be used for X-ray microanalysis of frozen-hydrated biological samples.

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.

Frontiers in electron probe microanalysis: application to cell physiology

The application of electron probe microanalysis techniques, using X-ray and electron energy loss instruments, to problems in cell physiology is reviewed. The details of the special methodological requirements for the analysis of cryosections at high spatial resolution in an analytical electron microscope are discussed together with a comprehensive review of data obtained on major organ systems and cell types.

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.

Quantitative digital X-ray imaging using frozen hydrated and frozen dried tissue sections

Application of quantitative X-ray imaging to frozen hydrated tissue sections has presented a number of major problems including lack of a suitable algorithm which could deal effectively with mass loss due to radiation damage, problems of low characteristic X-ray signal to background ratios, and provide a means of analysis of the same location in both hydrated and dried states. This paper presents details of the application of our algorithm for analysis of frozen hydrated, then dried cryosections applied to quantitative X-ray imaging, which provides relatively high precision quantitative measurement of elemental content (related to both wet and dry weight) and water content of each pixel. This algorithm largely circumvents many of the problems of analysis of frozen hydrated tissue sections. Our algorithm for X-ray imaging obtains reasonably precise quantitative measurements coupled with morphological information by trading speed and image resolution.

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.

Beam induced mass loss in high resolution biological microanalysis

Electron beam induced loss of mass from the organic matrix and from higher Z constituents of biological samples was measured by monitoring bremsstrahlung and peak changes in EDS spectra. When any effects of contamination, extraneous X-rays, beam current drift, specimen drift, and specimen shrinkage were monitored and corrected for, the three types of samples gave consistent and similar results at 296 K. Bremsstrahlung losses averaged 45%, 46% and 50% respectively for muscle homogenate, salivary gland sections and albumin. Sulphur losses average 74%, 72% and 86% for the same three sample types. No other elements suffered significant losses. D1/e for bremsstrahlung averaged 0.14 C/cm2. Bremsstrahlung loss at 93 K began approximately one order of magnitude higher in dose, and the extent of loss varied. Sulphur losses, however, were greatly reduced at low temperatures.

Properties of frozen sections relevant to quantitative microanalysis

Difficulties in the quantitative X-ray microanalysis of frozen sections may conceivably arise from ice-crystal damage and from electron-beam damage. X-ray peak-to-continuum ratios are commonly taken as a quantitative index of elemental concentrations. But recent reports suggest that in dehydrated frozen sections such ratios vary greatly with the scale of ice-crystal formation existing prior to sublimation. The experiments in these reports are re-interpreted here; it is argued that peak intensities may be affected by ice-crystal scale but that ratios of peak to continuum should not be affected after corrections for exogenous continuum. The accuracy of the peak-to-continuum method is affected by beam-induced loss of mass from microvolumes during analysis. Mass loss can be reduced or slowed by a cold-stage. For example, the radiation sensitivity for loss of chlorine from PVC is reduced by a factor of 1000 or more with reduction of temperature from 300 to 100 K. For sections of soft tissue the effectiveness of cooling is not nearly so striking but at 100 K, analyses of 1 micron frozen-hydrated sections by the continuum method, with spatial resolution of the order of 1 micron, can be completed before substantial mass loss occurs. However, analysis of frozen-hydrated sections by the continuum method at much higher resolution, say 100 nm resolution in 100 nm sections, is precluded by mass loss. Measurements of local mass can be achieved with much lower dose by observation and calibration of the electron transmission or backscattering. But even with these methods, several problems remain in achieving quantitative X-ray analysis at very high resolution.

Rat renal papilla: comparison of two techniques for x-ray analysis

Major differences in elemental and water content in cells of rat papillae have been reported by investigators using the frozen hydrated/frozen dried method versus that using external standards for x-ray microanalysis. These differences could not be ascribed to either cryosectioning at warmer temperatures or to the analytical algorithm used by either group. In this study, six paired left and right renal papillae were subjected to x-ray analysis. The frozen hydrated/frozen dried method was used on undipped papilla, while both methods were applied simultaneously to contralateral papillae dipped in albumin standard. No significant differences were seen between the physiologic state of the left and right kidneys prior to freezing. Our results demonstrated two major problems with application of an albumin peripheral standard: 1) albumin dipping significantly changed elemental and water content in papillary collecting duct cells, epithelial cells and interstitium, but interstitial cells were not affected; 2) the peripheral albumin standard itself also changed water and elemental content in a direction consistent with movement of Na and Cl from tissue to standard, and water from standard to tissue.

Simultaneous comparison of techniques for x-ray analysis of proximal tubule cells

Major differences in elemental and water content in cells of rat papillae in antidiuresis have been reported using x-ray microanalysis. The reason for these reported differences in unknown. In order to determine if the differing microprobe techniques used in these reports could account for the differences measured, we analyzed elemental concentrations in rat proximal tubule cells using both methods simultaneously on the same cells. Both methods provided comparable results. Furthermore, no differences in element or water content of proximal tubule cells cryosectioned with albumin at -53 degrees C and those cells cryosectioned at -80 degrees C were seen. Therefore, the differing values previously reported for elemental analysis of rat kidney cannot be ascribed to either cryosectioning at a warmer temperature or to the analytical algorithm used by either group.