Cation-chromatin binding as shown by ion microscopy is essential for the structural integrity of chromosomes.

Mammalian interphase and mitotic cells were analyzed for their cation composition using a three-dimensional high resolution scanning ion microprobe. This instrument maps the distribution of bound and unbound cations by secondary ion mass spectrometry (SIMS). SIMS analysis of cryofractured interphase and mitotic cells revealed a cell cycle dynamics of Ca2+, Mg2+, Na+, and K+. Direct analytical images showed that all four, but no other cations, were detected on mitotic chromosomes. SIMS measurements of the total cation content for diploid chromosomes imply that one Ca2+ binds to every 12.5-20 nucleotides and one Mg2+ to every 20-30 nucleotides. Only Ca2+ was enriched at the chromosomal DNA axis and colocalized with topoisomerase IIalpha (Topo II) and scaffold protein II (ScII). Cells depleted of Ca2+ and Mg2+ showed partially decondensed chromosomes and a loss of Topo II and ScII, but not hCAP-C and histones. The Ca2+-induced inhibition of Topo II catalytic activity and direct binding of Ca2+ to Topo II by a fluorescent filter-binding assay supports a regulatory role of Ca2+ during mitosis in promoting solely the structural function of Topo II. Our study directly implicates Ca2+, Mg2+, Na+, and K+ in higher order chromosome structure through electrostatic neutralization and a functional interaction with nonhistone proteins.

Contribution of organic material to the ion composition of bone.

Studies of bone mineral ranging from cadaveric analysis to the use of high-resolution ion microprobe with secondary ion mass spectroscopy (SIMS) have concluded that bone is rich in sodium and potassium relative to calcium. Exposure of bone to acid conditions either in vitro or in vivo leads to an exchange of hydrogen ions for sodium and potassium buffering the acidity of the medium or blood, respectively. Whether these monovalent ions reside within the mineral or organic phases of bone has never been determined. To determine the contribution of organic material to bone ion composition, we dissected calvariae from 4- to 6-day-old mice, removed organic material of some with hydrazine (Hydr), and prepared all bones for analysis using a high-resolution scanning ion microprobe coupled to a secondary ion mass spectrometer. We found that in non-Hydr-treated calvariae (Ctl) there was far more surface sodium and potassium than calcium (23Na/ 40Ca = 15.7 + 1.9, ratio of counts of detected secondary ions, mean + 95% CI, 39K/40Ca = 44.0 + 1.5). Removal of organic material with hydrazine (Hydr) led to a marked fall in the ratio of sodium to calcium and potassium to calcium (23Na/40Ca = 5.9 + 1.4, p < 0.025 vs. respective Ctl and 39K/40Ca = 1.1 + 1.5, p < 0.001 vs. respective Ctl). Similarly, when examining the cross-section of the calvariae there was more sodium and potassium than calcium (23Na/40Ca = 8.6 + 1.6, 39K/40Ca = 26.7 + 1.8). Treatment with Hydr again caused a marked fall in both ratios (23Na/40Ca = 0.3 + 1.6, p < 0.001 vs. respective Ctl and 39K/40Ca = 0.02 + 1.9, p < 0.001 vs. respective Ctl). Thus, within bone the organic material contains the majority of the sodium and potassium. This suggests that the organic material in bone and not the mineral itself is responsible for the acute buffering of the additional hydrogen ions during metabolic acidosis.

Effects of in vivo metabolic acidosis on midcortical bone ion composition.

Chronic metabolic acidosis increases urine calcium excretion without altering intestinal calcium absorption, suggesting that bone mineral is the source of the additional urinary calcium. During metabolic acidosis there appears to be an influx of protons into bone mineral, lessening the magnitude of the decrement in pH. Although in vitro studies strongly support a marked effect of metabolic acidosis on the ion composition of bone, there are few in vivo observations. We utilized a high-resolution scanning ion microprobe with secondary ion mass spectroscopy to determine whether in vivo metabolic acidosis would alter bone mineral in a manner consistent with its purported role in buffering the increased proton concentration. Postweanling mice were provided distilled drinking water with or without 1.5% NH(4)Cl for 7 days; arterial blood gas was then determined. The addition of NH(4)Cl led to a fall in blood pH and HCO(-)(3) concentration. The animals were killed on day 7, and the femurs were dissected and split longitudinally. The bulk cortical ratios Na/Ca, K/Ca, total phosphate/carbon-nitrogen bonds [(PO(2) + PO(3))/CN], and HCO(-)(3)/CN each fell after 1 wk of metabolic acidosis. Because metabolic acidosis induces bone Ca loss, the fall in Na/Ca and K/Ca indicates a greater efflux of bone Na and K than Ca, suggesting H substitution for Na and K on the mineral. The fall in (PO(2) + PO(3))/CN indicates release of mineral phosphates, and the fall in HCO(-)(3)/CN indicates release of mineral HCO(-)(3). Each of these mechanisms would result in buffering of the excess protons and returning the systemic pH toward normal.

A secondary ion mass spectroscopic study of the elemental composition pattern in rat incisor dental enamel during different stages of ameloblast differentiation.

In most earlier studies on the elemental composition pattern of dental enamel, a picture is presented which describes a limited region. In this study, estimates of the incorporation of some critical elements into enamel were correlated with the differentiation stages of the ameloblasts through out the whole tooth. Elemental analyses of rat incisor dental enamel during the secretory, transitional and maturation phases were performed using two different modes of secondary ion mass spectrometry (SIMS). The results were presented as ion images and three-dimensional spatial resolution graphs. In the elemental images of 23Na, 26CN, 35Cl and 39K, counts were detected during the secretory and maturation phases of amelogenesis. Variations were interpreted as resulting from secretion of elements during the secretory phase and resorption during the maturation phase. In line scans the ion yield from enamel during different stages of differentiation of the ameloblasts was analysed. The elements investigated were 12C, 19F, 23Na, 31P, 39K and 77CaCl. As seen in the images, most elements exhibited a higher ion yield during the earlier stages of secretion, and lower yields during the maturation-phase resorption. Cl, together with P, increased during the phases of maturation. In the most apical portions of the teeth, corresponding to a presecretory phase, an inverse pattern was seen for most of the elements. If the surface yield was high at the onset of the secretory phase, the presecretory yields were lower, and vice versa.

Effect of metabolic acidosis on the potassium content of bone.

Metabolic acidosis induces resorption of cultured bone, resulting in a net efflux of calcium (Ca) from the bone and an apparent loss of mineral potassium (K). However, in these organ cultures, there is diffusion of K between the medium and the crystal lattice, causing difficulty in interpretation of the acid-induced changes in mineral ion composition. To determine the effects of acidosis on bone mineral K, we injected 4-day-old neonatal mice with pure stable isotope 41K, equal to approximately 5% of their total body K. Calvariae were dissected 24 h later and then cultured for 24 h in medium without added 41K, either at pH approximately 7.4 (Ctl) or at pH approximately 7.1 (Ac), with or without the osteoclastic inhibitor calcitonin (3 x 10(-9) M, CT). The bone isotopic ion content was determined with a high-resolution scanning ion microprobe utilizing secondary ion mass spectrometry. 41K is present in nature at 6.7% of total K. The injected 41K raised the ratio of bone 41K/(39K+41K) to 9.8+/-0.5% on the surface (ratios of counts per second of detected secondary ions, mean+/-95% confidence interval) but did not alter the ratio in the interior (6.9+/-0.4%), indicating biological incorporation of the 41K into the mineral surface. The ratios of 41K/40Ca on the surface of Ctl calvariae was 14.4+/-1.2, indicating that bone mineral surface is rich in K compared with Ca. Compared with Ctl, Ac caused a marked increase in the net Ca efflux from bone that was blocked by CT. Ac also induced a marked fall in the ratio of 41K/40Ca on the surface of the calvariae (43+/-0.5, p < 0.01 vs. Ctl), which was partially blocked by CT (8.2+/-0.9, p < 0.01 vs. Ctl and vs. Ac), indicating that Ac causes a greater release of bone mineral K than Ca which is partially blocked by CT. Thus, bone mineral surface is rich in K relative to Ca, acidosis induces a greater release of surface mineral K than Ca, and osteoclastic function is necessary to support the enriched levels of surface mineral K in the presence of acidosis.

Imaging of BrdU-labeled human metaphase chromosomes with a high resolution scanning ion microprobe.

Detailed maps of the A-T distribution within human mitotic chromosomes labeled with BrdU are obtained with a high resolution scanning ion microprobe through the detection of bromine by imaging secondary ion mass spectrometry (SIMS). Corresponding maps of the emission loci of the molecular ion CN- describe the overall DNA, RNA and protein distribution in the chromosomes. Several chromosome preparations exhibit base-specific banding patterns (SIMS-bands) which mimic the well known G- or Q-bands resulting from conventional staining methods for optical microscopy. SIMS-bands are more noticeable in mitotic cells at the first cell cycle and after in situ denaturation or Giemsa staining. Sister chromatid exchanges (SCE) at the second cell cycle and beyond, occurring both spontaneously and promoted following cell culture exposure to the chemical aphidicolin (an inhibitor of DNA replication), can be visualized readily from the relative label signal intensities between sister chromatids. The comparison of base-specific label maps with CN- maps, in conjunction with the appearance of base-specific banding patterns, is informative about protein survival and/or removal following different chromosome preparation protocols. In addition, the resulting condensation state of the chromosomes can be appraised during SIMS analysis from the sample topography (imaged via the collection of mass-unresolved secondary ions). We demonstrate that imaging SIMS is a powerful complement to existing methods for the study of banding mechanisms and for the elucidation of chromosome structure. The advantages of this novel approach to the systematic and quantitative study of cytogenetic phenomena and methodologies are still largely untapped.

Effects of osteoclastic resorption on bone surface ion composition.

Osteoclasts are responsible for resorption of bone mineral. To determine how osteoclasts alter bone surface ion composition, neonatal mouse bone cells were isolated and cultured in the presence of parathyroid hormone (PTH) on bovine cortical bone. Surface ion composition of the resulting osteoclastic resorption pits was compared with that of unresorbed bone, utilizing a high-resolution scanning ion microprobe. Cortical bone cultured with cells in the presence of PTH had numerous resorption pits. The unresorbed area adjacent to the pits had a ratio of surface 23Na/40Ca of 18.7 + 1.6 (mean counts per second of detected secondary ions +95% confidence interval) and 39K/40Ca of 2.3 + 2.2. At the base of the pits, the ratio of 23Na/40Ca was 1.0 + 2.0 and 39K/40Ca was 0.1 + 1.0 (each different from area adjacent to the pit, P < 0.001). The ratio of 23Na/39K in the unresorbed area was not different from that at the base of the pit. Thus osteoclasts induce a decrease in the ratio of surface ion composition of both 23Na/40Ca and 39K/40Ca but not 23Na/39K in bovine cortical bone. The elevated ratios of 23Na/40Ca and 39K/40Ca on the surface, but not at the base of the pits, indicate adsorption of medium ions onto the mineral. Because osteoclasts foster the release of bone Ca, these results indicate that osteoclastic resorption causes a greater, and approximately equal, release of both 23Na and 39K compared with 40Ca from bone mineral. Osteoclasts appear to remove nonselectively the surface mineral that had been exposed to the medium, uncovering underlying mineral.

Advances in high resolution SIMS studies of BrdU-labelled human metaphase chromosomes.

The detection of bromine in human metaphase chromosomes labelled with the thymidine-analog BrdU, by imaging Secondary Ion Mass Spectrometry (SIMS) with a high resolution scanning ion microprobe, provides detailed maps of the AT distribution within the chromosomes. Similarly, maps of the emitted CN-molecular ions describe the overall DNA, RNA and protein distribution, details of which are also revealed by maps of the divalent cations Ca+ and Mg+. Base-specific banding patterns (SIMS bands), mimicking the well known G-or Q-bands resulting from conventional staining methods for optical microscopy, are observed in several preparations, more noticeably in mitotic cells at the first cell division, after in situ DNA denaturation, or Giemsa staining. A structured distribution, seemingly related to G/Q-banding patterns, is also observed in the Mg+ and Ca+ maps. The differential label signal intensities between sister chromatids, at the second cell division and beyond, manifest the occurrence of sister chromatid exchanges (SCE), occurring both spontaneously and induced following exposure of the cells to the chemical aphidicolin (an inhibitor of DNA replication). Imaging SIMS emerges as a powerful investigative method for the study of chromosome structure and the elucidation of banding mechanisms, to assess the removal of proteins and DNA involved in chromosome preparation and in situ procedures, and in the study of a number of cytogenetic phenomena.

Effects of aluminum on bone surface ion composition.

Aluminum induces net calcium efflux from cultured bone. To determine whether aluminum alters the bone surface ion composition in a manner consistent with predominantly cell-mediated resorption, a combination of cell-mediated resorption and physicochemical dissolution or physicochemical dissolution alone, we utilized an analytic high-resolution scanning ion microprobe with secondary ion mass spectroscopy to determine the effects of aluminum on bone surface ion composition. We cultured neonatal mouse calvariae with or without aluminum (10(-7) M) for 24 h and determined the relative ion concentrations of 23Na, 27Al, 39K, and 40Ca on the bone surface and eroded subsurface. Control calvariae have a surface (depth approximately 6 nm) that is rich in Na and K compared with Ca(Na/Ca) = 24.4 + 1.4, mean + 95% confidence limit of counts per second of detected secondary ions, K+Ca = 13.2 + 0.9). Aluminum is incorporated into the bone and causes a depletion of surface Na and K relative to Ca (Na/Ca = 9.6 + 0.7, K/Ca = 4.9 + 0.4; each p < 0.001 versus control). After erosion (depth approximately 50 nm), control calvariae have more Na and K than Ca (Na/Ca = 16.0 + 0.1, K/Ca = 7.5 + 0.1); aluminum again depleted Na and K relative to Ca (Na/Ca = 4.1 + 0.1 K/Ca = 1.9 + 0.1; each p < 0.001 versus control). Aluminum produced a greater net efflux of Ca (362 +/- 53, mean +/- SE, nmol/bone/24 h) than control (60 +/- 30, p < 0.001). With aluminum, the fall in the ratios of both Na/Ca and K/Ca coupled with net Ca release from bone indicates that aluminium induces a greater efflux of Na and K than Ca from the bone surface and is consistent with an aluminum-induced removal of the bone surface. This alteration in surface ion concentration and calcium efflux is consistent with that observed when calcium is lost from bone through a combination of cell-mediated resorption and physicochemical dissolution.

Nucleotide and protein distribution in BrdU-labelled polytene chromosomes revealed by ion probe mass spectrometry.

Detailed chemical maps of BrdU-labelled polytene chromosomes of Drosophila melanogaster, obtained by imaging secondary ion mass spectrometry, reveal separately the distribution of DNA and proteins in the chromosomes. The thymidine-analogue BrdU within the chromosomal DNA is localized by detecting the Br- secondary ion signal, while both nucleic acid and protein content are mapped through the abundantly emitted CN- signal. This novel approach supercedes, and helps explain the origin of, the banding patterns that are observed by conventional staining techniques. The high spatial resolution and chemical and isotopic sensitivity of this technique should enhance the localization of specific genes by in situ hybridization in mitotic chromosomes.

The use of the stable isotope 44Ca in studies of calcium incorporation into dentin.

The incorporation into rat incisor dentin of two calcium isotopes, the stable 44Ca and the radioactive 45Ca, was studied using secondary ion mass spectrometry (SIMS) step-scanning and imaging, and autoradiography, respectively. The results demonstrated a time-dependent incorporation of the calcium isotopes into the mineral phase of dentin. With the SIMS step-scanning, detecting 44Ca, the ion yield was high in the odontoblasts 2 min after intravenous injection. After 10 min a marked increase in signal intensity was found at the dentin mineralization front. This result was consistent with those obtained by 45Ca autoradiography; a peak of incorporation occurred 10 min after injection of the isotope. Likewise, localization of 44Ca to the mineralization front could be demonstrated 10 min after injection by SIMS imaging. In images obtained at earlier intervals, no such increase in ion yield could be detected. The results show that the nonradioactive, stable isotope 44Ca can be used as a marker for biomineralization in a similar way to radioactive 45Ca.

The absence of correlations between a clinical classification and ultrastructural findings in amelogenesis imperfecta.

This study was performed to examine whether a clinical classification of different phenotypes of amelogenesis imperfecta could be discernible at the ultrastructural level. Seventeen primary teeth from 16 children with hypomineralization, hypomaturation, or hypoplastic variants of the disease were collected for histologic studies of the enamel by means of polarized light microscopy, scanning electron microscopy (SEM), and secondary ion mass spectrometry (SIMS). Polarization microscopy showed that the enamel was hypomineralized; in six teeth a wavy configuration of the enamel prisms also appeared. Three histomorphologic main types could be discerned. In 10 of the teeth extensive hypomineralization of the bulk of the enamel was found. One tooth had an unusually thick enamel with only a thin normally mineralized surface layer. SIMS images showed less pronounced signals from Ca2+ and Na+ but with stronger signals from Cl- and CN-, representing the organic component of enamel. The SEM images showed an irregular prism pattern with marked interprismatic areas. Irrespective of the clinical appearance or the hereditary pattern the main findings were hypomineralized enamel with or without wavy bands. Neither of the analytical methods used in this paper distinguishes between the clinical phenotypes of amelogenesis imperfecta.

Physicochemical effects of acidosis on bone calcium flux and surface ion composition.

Net calcium flux (JCa) from bone in vitro is pH dependent. When pH falls below 7.40, through a reduction in [HCO3-], there is both physicochemical and cell-mediated JCa. To characterize the physicochemical effect of acidosis on bone we inhibited the bone-resorbing cells (osteoclasts) with the specific inhibitor calcitonin and studied the effect of acidosis on JCa and bone ion composition using an analytic high-resolution scanning ion microprobe. Neonatal mouse calvariae were cultured for 48 h in physiologically neutral pH medium (Ntl, pH = 7.41, [HCO3-] = 25 nM) or in medium that modeled metabolic acidosis (Met, pH = 7.10, [HCO3-] = 12), each with or without calcitonin (CT, 3 x 10(-9) M). There was net calcium efflux in Ntl (JCa = 631 +/- 36 nmol per bone per 48 h), which increased in Met (1019 +/- 53, p < 0.01); CT inhibited JCa in Ntl (-54 +/- 11, p < 0.01 versus Ntl), which increased in Met (197 +/- 15, p < 0.01 versus Ntl + CT). In the presence of CT the increase in JCa in Met versus Ntl represents physiochemical bone dissolution. The Ntl bone surface (approximately 2 nm in depth) was rich in Na compared to Ca (Na/Ca = 11.9, count/s of detected secondary ions), which fell in Met (Na/Ca = 6.0, p < 0.05); CT caused a further reduction of Na/Ca (3.1, p < 0.01 versus Ntl and versus Met), which was not altered in Met (2.6, p < 0.05 versus Ntl + CT).(ABSTRACT TRUNCATED AT 250 WORDS)

Cytogenetic applications of high resolution secondary ion imaging microanalysis: detection and mapping of tracer isotopes in human chromosomes.

Analytical imaging by secondary ion mass spectrometry (SIMS) using a state-of-the-art scanning ion microprobe enables the detection and mapping of tracer isotopes in human metaphase chromosomes. The stimulated mitosis of cells cultured in media containing labelled nucleosides, typically 14C-labelled thymidine or adenosine, and BrDU, yields chromosomes that have incorporated the labelled molecule in their constituent DNA. The label is subsequently detected and localized by SIMS imaging. The relative label signal intensities of sister chromatids can be quantified. The occurrence of sister chromatid exchanges (SCE) can be detected. The distribution of specific nucleosides can be directly mapped. This is non-uniform along the chromatids, giving rise to characteristic banding patterns (SIMS bands) that seem to correspond to the well known G- or Q-bands resulting from conventional staining methods. The study of a number of cytogenetic problems is expected to benefit from the use of this new method of approach, similar in principle, but potentially more sensitive and capable of higher spatial resolution than autoradiography.

Alteration in surface ion composition of cultured bone during metabolic, but not respiratory, acidosis.

Acidosis produced by a fall in [HCO3-] (metabolic acidosis, Met) produces greater Ca efflux from cultured bone than that produced by a rise in PCO2 (respiratory acidosis, Resp). To compare the effects of Met and Resp on bone surface ion composition we measured the surface abundance of 40Ca, 23Na, and 39K in cultured bone with a scanning ion microprobe utilizing secondary-ion mass spectrometry. Neonatal mouse calvariae were incubated for 24 h in medium simulating either Met (pH = 7.193 +/- 0.034, [HCO3-] = 15.1 +/- 1.4 meq/l), Resp (pH = 7.153 +/- 0.014, PCO2 = 85.4 +/- 1.2 mmHg) or normal physiological (Ctl; pH = 7.484 +/- 0.009, [HCO3-] = 29.7 +/- 0.7, PCO2 = 39.6 +/- 0.3) conditions. The surface of Ctl at 2-nm depth is rich in Na and K relative to Ca (Na/Ca = 25.6, K/Ca = 12.0, ratios of counts/s of secondary ions). Compared with Ctl, Met produced a sharp fall in both Na/Ca (6.5, P less than 0.01) and K/Ca (4.6, P less than 0.01), whereas Resp did not alter Na/Ca (23.8) or K/Ca (15.0). Ca efflux was greater in Met (873 +/- 54 nmol.bone-1.24 h-1) than in Resp (546 +/- 71 nmol.bone-1.24 h-1, P less than 0.01), which was greater than that in Ctl (315 +/- 49 nmol.bone-1.24 h-1, P less than 0.01 vs. Met and vs. Resp).(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of in vitro and in vivo 44Ca labeling of bone by scanning ion microprobe.

To determine whether Ca incorporation from medium into cultured bone represents normal mineralization, we labeled some neonatal mouse calvariae in vitro and others in vivo with the stable isotope 44Ca and compared surface label localization with a scanning ion microprobe utilizing secondary ion mass spectrometry. To label in vitro, we incubated live calvariae in medium containing 40Ca or 44Ca for 3 h. Compared with a 44Ca/40Ca ratio of 0.020 with 1 mM 40Ca, the ratio with 1 mM 44Ca was 0.135 and with 2 mM 44Ca was 0.556. Erosion revealed a marked decrease in 44Ca/40Ca with depth. To label in vivo, we subcutaneously injected 40Ca or 44Ca into mice equal to a percentage of their total body weight and dissected the calvariae 24 h later. Compared with a 44Ca/40Ca ratio of 0.021 with 2% 40Ca, the ratio with 2% 44Ca was 0.120 and with 6% 44Ca was 0.205. Erosion revealed only a slight decrease in 44Ca/40Ca with depth. Elemental distribution maps of in vivo labeled samples show broad deposition of 44Ca, whereas maps of in vitro labeled bones show 44Ca preferentially localized at the surface in contact with the medium. Thus calvariae can be labeled with 44Ca both in vitro and in vivo. However, the differing patterns of isotope localization under the conditions of this study indicate that in vitro Ca deposition differs from normal in vivo bone mineralization.

Scanning ion microprobe assessment of biological sample preparation techniques.

Different preparation techniques for high lateral resolution scanning ion microprobe imaging of biological samples have been investigated. The sharpest histological maps are obtained from chemically fixed and plastic embedded specimens. It is often problematic to correlate ultrastructure and bioaccumulation from analysis of frozen cut and lyophilized sections. The best compromise is to resin-embed frozen samples in order to get a perfectly flat section from tissue where the in vivo ion distribution is maintained. Use of the University of Chicago Ion Microprobe gave us the ability to observe the relative ion translocations induced during sample preparation. As an example, we show the rapid decrease of intracellular K+/Na+ ratio through a fast frozen blood droplet.

Ion microprobe analysis of bone surface elements: effects of 1,25(OH)2D3.

When neonatal mouse calvariae are incubated with 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] there is net calcium efflux from the bone into the medium. The effect of this enhanced cell-mediated Ca efflux on the relative concentrations of mineral 23Na, 39K, and 40Ca has not previously been studied. We used an imaging scanning ion microprobe, utilizing secondary ion mass spectrometry, to compare the relative ion concentrations of Na, K, and Ca on the surface, subsurface, and cross-section of cultured bone incubated in the presence of 1,25(OH)2D3 with the ion concentrations in similar regions of bone incubated in unaltered control medium. Changes in mineral ion concentration were correlated with net fluxes of Na, K, and Ca relative to bone. Calvariae incubated in control medium (24 h at pH approximately 7.40) have abundant surface Na and K relative to Ca (Na/Ca, 85 and K/Ca, 68), whereas the subsurface has less Na/Ca (21) and K/Ca (23), and on cross section the ratios of both Na/Ca (2.0) and K/Ca (1.9) decrease further. After incubation with 10(-8) M 1,25(OH)2D3, there is a significant increase in bone surface Na/Ca (154) and K/Ca (141) without a change in these ratios on the subsurface and a small fall in both ratios on cross section. The linear relationship between Na/Ca and K/Ca across the three regions of bone observed in control calvariae did not change with 1,25(OH)2D3 treatment. As determined by flux measurements there is a net efflux of Ca but not Na or K from bone.(ABSTRACT TRUNCATED AT 250 WORDS)

Trifluorothymidine localization in the rabbit cornea by secondary ion mass spectrometry imaging microanalysis.

Imaging microanalysis by secondary ion mass spectrometry is a sensitive surface analytical technique that allows the detection and localization of elements and compounds in biological tissues. We report the detection by this approach of intracorneal trifluorothymidine following topical administration in rabbit with normal cornea. The presence of trifluorothymidine is revealed using 19F as a marker, allowing the acquisition of ultrastructural microanalytical images without using radioactive tracers.