Calcium Distribution Patterns Research Articles

Calcium Distribution Patterns of the Aorta as Predictors of Significant Coronary Artery Disease in Patients with Moderate to Severe Aortic Stenosis

OBJECTIVE Computed tomography (CT) of the aortic valve and aorta has gained a greater role in planning for aortic valve replacement (AVR). However, when AVR is planned, invasive coronary angiography remains the standard investigation. Whether the calcium distribution pattern in the aorta predicts the significant presence of coronary artery disease (CAD) in patients undergoing AVR remains unclear. This study evaluated the correlation between the calcium distribution pattern from the CT aorta to predict significant CAD in patients with symptomatic moderate to severe aortic stenosis undergoing AVR. METHODS This retrospective study included candidates for AVR either with transcatheter replacement (TAVR) or surgical replacement (SAVR) at a single tertiary-care center between 2017 and 2022. The calcium distribution patterns from the left ventricular outflow tract up to the descending aorta were analyzed from the non-contrast CT of the aorta. Significant CAD was identified from invasive coronary angiography and was defined as 50% diameter stenosis (DS) of the left main and 70% DS of the proximal left anterior descending artery. Multivariate logistic regression analysis was performed to identify the calcification pattern associated with the significant CAD. RESULTS In total, 110 patients were included in the analysis. Among them, 40 patients (36.4%) were candidates for TAVR, while 70 patients (63.6%) were candidates for SAVR. The prevalence of significant CAD was 12.7%. Baseline characteristics were similar between patients with and without CAD, with the exception of a higher prevalence of chronic kidney disease in the CAD group (42.9% vs. 19.8%, p = 0.01). The presence of calcium at the ostium of the coronary artery and descending aorta was an independent predictor of significant CAD (OR 3.44, 95% CI1.30-9.10, p = 0.01 and OR 12.03, 95% CI 1.14-126.84, p = 0.04). CONCLUSIONS This pilot study showed that calcium at the ostium of the coronary artery and descending aorta from non-contrast CT aorta was associated with significant CAD in patients with moderate to severe AS. Further study with more subjects be needed to confirm the findings. KEYWORDS calcium distributions; aortic stenosis; coronary artery disease; computed coronary angiography

Abstract 14960: Coronary Artery Calcium Distribution Patterns Are Independently Predictive of Adverse Cardiovascular Events: Observations From the Dallas Heart Study

Introduction: The coronary artery calcium (CAC) diffusivity index (DI) may improve risk stratification for those with Agatston CAC > 0 in older individuals. We aimed to assess whether the distribution of CAC would improve risk prediction of cardiovascular (CV) events beyond the traditional Agatston CAC score in a younger population. Methods: Among Dallas Heart Study 2 (DHS2) participants with Agatston CAC > 0 and no history of CVD (35% of entire cohort), we studied 1013 participants with CAC DI at DHS2. The raw CAC DI was calculated as 1 - (CAC in most affected vessel/total CAC) and categorized into concentrated (<25th%), standard (25-75th%), and diffuse (>75th%) patterns. Multivariable Cox proportional hazards regression and C statistics were calculated for coronary events (CHD) and all CVD, and all-cause mortality. Models were adjusted for total Agatston score, race, gender, BSA, smoking history, diabetes, and statin use. Results: Mean age of the DHS2 study cohort was 55 ± 9.4 years (48% women, 45% Black). The median follow up was 9 ± 2.5 years (55 CHD, 97 CVD, and 120 all-cause mortality events) (Figure, A) . CAC DI was modestly correlated with Agatston CAC (Spearman rho = 0.60, p<0.01). In models adjusted for total Agatston score, risk factors, and demographics, compared with a concentrated pattern, a diffuse CAC pattern was associated with incident CHD (HR [95%CI]: 5.32 [1.68-16.86]); CVD (HR [95%CI]: 3.21 [1.66-6.21]), and all-cause mortality (HR [95%CI]: 2.02 [1.18-3.47] (Figure, B) . Findings were similar for continuous CAC DI. Addition of continuous CAC DI to adjusted models including Agatston CAC improved the C-statistic for CHD (0.79 to 0.81, p<0.01) and CVD (0.71 to 0.73, p<0.01). Conclusions: Beyond the validated Agatston score, higher CAC DI at baseline improves risk prediction of incident CHD and CVD events in a younger population-based cohort. Further studies are warranted to evaluate the clinical utility of assessing distribution patterns of CAC.

Peripheral arterial disease treatment planning using noninvasive and invasive imaging methods

With the growing prevalence and mortality of peripheral arterial disease, preoperative assessment, risk stratification, and determining the correct indication for endovascular and open surgical procedures are essential for therapeutic decision-making. The effectiveness of interventional procedures is significantly influenced by the plaque composition and calcification pattern. Therefore, the identification of patients for whom endovascular treatment is the most appropriate therapeutic solution often remains a challenge. The most commonly used imaging techniques have their own limitations and do not provide findings detailed enough for specific, personalized treatment planning. Using state-of-the-art noninvasive and invasive imaging modalities, it is now possible to obtain a view, not only of the complex vascular anatomy and plaque burden of the lower extremity arterial system, but also of complex plaque structures and various pathologic calcium distribution patterns. In the future, as these latest advancements in diagnostic methods become more widespread, we will be able to obtain more accurate views of the plaque structure and anatomic complexity to guide optimal treatment planning and device selection. We reviewed the implications of the most recent invasive and noninvasive lower extremity imaging techniques and future directions.

Biomineralization of three calcium silicate-based cements after implantation in rat subcutaneous tissue.

ObjectivesThe aim of this study was to evaluate the dystrophic mineralization deposits from 3 calcium silicate-based cements (Micro-Mega mineral trioxide aggregate [MM-MTA], Biodentine [BD], and EndoSequence Root Repair Material [ESRRM] putty) over time after subcutaneous implantation into rats.Materials and MethodsForty-five silicon tubes containing the tested materials and 15 empty tubes (serving as a control group) were subcutaneously implanted into the backs of 15 Wistar rats. At 1, 4, and 8 weeks after implantation, the animals were euthanized (n = 5 animals/group), and the silicon tubes were removed with the surrounding tissues. Histopathological tissue sections were stained with von Kossa stain to assess mineralization. Scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM/EDX) were also used to assess the chemical components of the surface precipitates deposited on the implant and the pattern of calcium and phosphorus distribution at the material-tissue interface. The calcium-to-phosphorus ratios were compared using the non-parametric Kruskal-Wallis test at a significance level of 5%.ResultsThe von Kossa staining showed that both BD and ESRRM putty induced mineralization starting at week 1; this mineralization increased further until the end of the study. In contrast, MM-MTA induced dystrophic calcification later, from 4 weeks onward. SEM/EDX showed no statistically significant differences in the calcium- and phosphorus-rich areas among the 3 materials at any time point (p > 0.05).ConclusionsAfter subcutaneous implantation, biomineralization of the 3-calcium silicate-based cements started early and increased over time, and all 3 tested cements generated calcium- and phosphorus-containing surface precipitates.

Identifying geogenic and anthropogenic controls on different spatial distribution patterns of aluminium, calcium and lead in urban topsoil of Greater London Authority area

Quantifying variation of metals in urban soils is crucial for efficient environmental and public health management. Prior to the interferences of human activities, regional topsoil geochemical distributions were generally primarily controlled by the underlying parent materials (PMs). With the rapid urbanisation, urban topsoil geochemical distributions have been modified with different levels. Three metals, aluminium (Al), calcium (Ca) and lead (Pb), were chosen to investigate the different levels of geogenic and anthropogenic controls in urban topsoil of Greater London Authority (GLA) area. These three metal elements clearly demonstrated the different spatial distribution affected by human activities using analysis of variance (ANOVA) and GIS-based spatial analysis. The high values of Al were in the clay which is located in the north and south GLA area; Pb accumulated in built-up areas and near traffic roads, which was likely associated with leaded paints and leaded petrol, respectively; the high Ca concentrations were in the Chalk bedrock of the southern GLA area and historical deconstruction and reconstruction sites in the city centre. Based on spatial interpolation and hot spot analysis (local Moran's I), this study reveals the different levels of geogenic and anthropogenic controls on different chemicals in urban soils: while the spatial distribution of Pb, which is more easily affected by human activities, can be significantly changed, the inert element Al may still be able to maintain its natural spatial distribution even in the heavily urbanized GLA area, and Ca demonstrates the mixed spatial distribution affected by both natural factors and human activities.

Disparity in spatial distribution of pericardial calcifications in constrictive pericarditis

BackgroundPericardial calcification is seen among patients with constrictive pericarditis (CP). However, the pattern of pericardial calcium distribution and the association with clinical outcomes and imaging data are not well described.MethodsThis...

Predictors of paravalvular regurgitation and permanent pacemaker implantation after TAVR with a next-generation self-expanding device.

To identify predictors of paravalvular regurgitation (PVR) and permanent pacemaker implantation (PPI) following TAVR with a next-generation self-expanding device. Device landing zone (DLZ) calcification, angiographic implantation depth, and baseline and procedural characteristics were analyzed in 212 patients being treated with the ACURATE neo aortic bioprosthesis. PVR was none/trace in 57.1% and ≥ mild in 42.9% (37% mild, 6% moderate). DLZ calcification (705 (IQR 240-624) vs. 382 (IQR 240-624)mm3; P < 0.001) as well as absolute calcium asymmetry (233 ± 159 vs. 151 ± 151mm3; P < 0.001) was significantly higher in patients with PVR ≥ mild. On multivariate analysis, calcification of the aortic valve cusps (AVC) > 410.6mm3 was independently associated with PVR ≥ mild. PPI rate was 10.3% (n = 20). Patients with and without need for PPI had similar total DLZ calcium volume (740 (IQR 378-920) vs. 536 (IQR 315-822)mm3; P = 0.263), but exhibited different calcium distribution patterns: LVOT calcium > 41.4mm3 in the sector below the left coronary cusp (LVOTLC) was associated with increased PPI risk (26.9 vs. 7.7%; P = 0.008). The quantity of AVC calcium predicts residual PVR. Multivariable analysis identified LVOTLC calcium, pre-existing RBBB, and age > 82.7years as independent predictors of PPI. Based on these risk factors, a patient's individual PPI risk can be stratified ranging from 3.8 to 100%.

Foliar Nutrient Distribution Patterns in Sympatric Maple Species Reflect Contrasting Sensitivity to Excess Manganese.

Sugar maple and red maple are closely-related co-occurring tree species significant to the North American forest biome. Plant abiotic stress effects including nutritional imbalance and manganese (Mn) toxicity are well documented within this system, and are implicated in enhanced susceptibility to biotic stresses such as insect attack. Both tree species are known to overaccumulate foliar manganese (Mn) when growing on unbuffered acidified soils, however, sugar maple is Mn-sensitive, while red maple is not. Currently there is no knowledge about the cellular sequestration of Mn and other nutrients in these two species. Here, electron-probe x-ray microanalysis was employed to examine cellular and sub-cellular deposition of excessively accumulated foliar Mn and other mineral nutrients in vivo. For both species, excess foliar Mn was deposited in symplastic cellular compartments. There were striking between-species differences in Mn, magnesium (Mg), sulphur (S) and calcium (Ca) distribution patterns. Unusually, Mn was highly co-localised with Mg in mesophyll cells of red maple only. The known sensitivity of sugar maple to excess Mn is likely linked to Mg deficiency in the leaf mesophyll. There was strong evidence that Mn toxicity in sugar maple is primarily a symplastic process. For each species, leaf-surface damage due to biotic stress including insect herbivory was compared between sites with acidified and non-acidified soils. Although it was greatest overall in red maple, there was no difference in biotic stress damage to red maple leaves between acidified and non-acidified soils. Sugar maple trees on buffered non-acidified soil were less damaged by biotic stress compared to those on unbuffered acidified soil, where they are also affected by Mn toxicity abiotic stress. This study concluded that foliar nutrient distribution in symplastic compartments is a determinant of Mn sensitivity, and that Mn stress hinders plant resistance to biotic stress.

Finite element model to study two dimensional unsteady state calcium distribution in cardiac myocytes

The calcium signaling plays a crucial role in expansion and contraction of cardiac myocytes. This calcium signaling is achieved by calcium diffusion, buffering mechanisms and influx in cardiac myocytes. The various calcium distribution patterns required for achieving calcium signaling in myocytes are still not well understood. In this paper an attempt has been made to develop a model of calcium distribution in myocytes incorporating diffusion of calcium, point source and excess buffer approximation. The model has been developed for a two dimensional unsteady state case. Appropriate boundary conditions and initial condition have been framed. The finite element method has been employed to obtain the solution. The numerical results have been used to study the effect of buffers and source amplitude on calcium distribution in myocytes.

Melatonin in sperm biology: breaking paradigms.

Melatonin is a ubiquitous molecule, present in a wide range of organisms, and involved in multiple functions. Melatonin relays the information about the photoperiod to the tissues that express melatonin-binding sites in both central and peripheral nervous systems. This hormone has a complex mechanism of action. It can cross the cell plasma membrane and exert its actions in all cells of the body. Certain melatonin actions are mediated by receptors that belong to the superfamily of G-protein-coupled receptors (GPCRs), the MT1 and MT2 membrane. Melatonin can also bind to calmodulin as well as to nuclear receptors of the retinoic acid receptor family, RORα1, RORα2 and RZRβ. The purpose of this review is to report on recent developments in the physiological role of melatonin and its receptors. Specific issues concerning the biological function of melatonin in mammalian seasonal reproduction and spermatozoa are considered. The significance of the continuous presence of melatonin in seminal plasma with a fairly constant concentration is also discussed.

Fluorine analysis of human dentin surrounding resin composite after fluoride application by μ-PIGE/PIXE analysis

Abstract The use of fluoride for the prevention of caries is based on the transformation of hydroxylapatite to fluoroapatite in the presence of fluoride ions, thereby strengthening tooth structure. Adhesion of dentin and resin composite (tooth-colored restoration material) requires a dentin bonding system, since resin composite is not able to adhere to dentin directly. Demineralization of dentin by acid etching is an important step in the dentin bonding system, however, demineralization also introduces weaknesses in tooth structure. If the demineralized dentin could be strengthened by the application of fluoride, then the dentin–resin composite bond strength might also improve. To test this hypothesis, the present study evaluated the influence of fluoride applications on the strength of the dentin–resin composite bond by (1) tensile strength testing analyses, (2) SEM analyses of tooth structure, and (3) detection of calcium (Ca) and fluorine (F) distribution patterns by micro proton-induced X-ray emission (μ-PIXE) and micro proton-induced gamma-ray emission (μ-PIGE) analyses conducted at the Takasaki Ion Accelerators for Advanced Radiation Application (TIARA) at the Takasaki Advanced Radiation Research Institute (TARRI). In this study, the dentin in extracted human molars was exposed by grinding and the dentin was etched with 35% phosphoric acid. Fluoride was applied at two concentrations, 0.022% (100 ppm F) and 2.21% (10,000 ppm F) NaF solution, for two time periods, 30 and 60 s, prior to bonding the resin composite with the treated dentin. Controls were prepared in the same manner, but without the fluoride application. Bond strength was measured with a micro-tensile testing unit, and the fluorine and calcium distributions at the interface between dentin and resin composite were detected by μ-PIGE and μ-PIXE analysis, respectively. Results indicate that the 10,000 ppm F applications resulted in higher bond strengths than observed in either the 100 ppm F applications or the control group. In addition, PIGE analyses showed high concentrations of fluorine in the hybrid bonding layer of the 10,000 ppm F samples, suggesting that the fluorine contributes to the strength of the dentin–resin composite bond. Detection of fluoroapatite within the hybrid bonding layer suggests that bond strength involves remineralization processes.

Correlation of regional distribution and morphological pattern of calcification at CT coronary artery calcium scoring with non-calcified plaque formation and stenosis

To investigate whether regional calcification patterns at CT coronary artery calcium scoring (CCS) correlate with stenosis and non-calcified plaque formation. We studied 106 patients with quantitative catheter angiography (QCA), CCS, and coronary CT angiography (cCTA). CCS was determined globally and for each artery separately. The morphological pattern of each calcification was classified as calcified nodule, shell-like, or diffuse. cCTA studies were evaluated for non-calcified plaque. The global and regional CCS and the calcification pattern were correlated with stenosis >or=50% and non-calcified plaque. A total of 48/106 patients had stenosis >or=50% on QCA. There was weak correlation (r = 0.36) of the global CCS with stenosis. Correlation was stronger per vessel (r = 0.55-r = 0.67). Shell-like and diffuse calcifications were significantly (p = 0.0001) more frequently associated with >or=50% stenosis and non-calcified plaque (p = 0.04) than calcified nodules. As shown before, the global CCS does not correlate well with stenosis. However, regional calcium distribution and specific patterns of calcification are correlated with stenosis and non-calcified plaque. Thus, the specificity of CT calcium scoring for identifying individuals with obstructive disease could be improved by vessel-based rather than global quantification of calcium and by differentiating specific morphological patterns of calcification.

Stem and leaf sequestration of zinc at the cellular level in the hyperaccumulator Sedum alfredii

* Sedum alfredii is a fast-growing, high-biomass zinc (Zn) hyperaccumulator native to China. Here, the characteristics of in vivo Zn distribution in stems and leaves of the hyperaccumulating (HE) and nonhyperaccumulating ecotypes (NHE) of S. alfredii were investigated by synchrotron radiation X-ray fluorescence (SRXRF) analysis, together with a Zn probe. * Preferential Zn accumulation in leaf and stem epidermis was observed in both ecotypes, but to a much greater extent for HE. Epidermal Zn increased largely in leaves and stems of HE as exposure time was prolonged, while Zn saturation occurred relatively early in HE leaf mesophyll cells and stem vascular bundles. A second peak of Zn enrichment in stem and leaf vascular systems was shown in both ecotypes. However, the proportion of Zn accumulated in stem vascular bundles relative to other tissues was much greater for HE than for NHE. * Leaf and stem distribution patterns of phosphorus (P) and sulphur (S) in the HE were very like that for Zn, while the calcium (Ca) distribution pattern was the reverse of that for Zn. No such relationship was observed in NHE. * Our study mainly suggested that epidermal layers serve as important storage sites for accumulated Zn in the S. alfredii HE.

Comparison of Mineral Trioxide Aggregate's Composition with Portland Cements and a New Endodontic Cement

The aim of this study was to compare the compositions of mineral trioxide aggregates (MTAs), Portland cements (PCs), and a new endodontic cement (NEC). Our study also investigated the surface characteristics of MTA and NEC root-end fillings when immersed in normal saline. For part I, we prepared samples of 9 brands of MTAs, PCs, and NEC. The materials were imaged and analyzed by scanning electron microscopy (SEM) and energy dispersive x-ray analysis (EDXA). In part II, 3-mm-deep root-end preparations were filled with MTA or NEC and stored in normal saline for 1 week. Samples were imaged and analyzed by SEM and electron probe microanalysis (EPMA). EDXA investigations revealed differences in the dominant compounds of NEC, PCs, and MTAs. The major components of MTA and PC are the same except for bismuth. The most significant difference was the presence of higher concentrations of Fe (minor element) in gray MTA and PC when compared with white ones. EPMA results revealed remarkably different elements in MTA compared with surrounding dentin, whereas in the NEC group the distribution patterns of calcium, phosphorous, and oxygen were comparable. NEC differs chemically from MTAs and PCs and demonstrates comparable surface composition with adjacent dentin as a root-end filling material.

Statistical measures of distribution patterns of silicon and calcium in marine sedimentary layers

Abstract. We analyze electron microscope X-ray spectroscopy data of recent supratidal marine sediments. Statistical measures are used to characterize the distribution of silicon and calcium in different layers of the sediments. We also use cluster analysis and symbolic dynamics to filter measurement noise and to classify different density regions. This allows to calculate characteristic patch sizes which reflect the sizes of individual clastic grains and the corresponding pore sizes. Silicon indicates the independent processes in the sedimentation history of certain grains. Calcium is capable to monitor intrinsic early diagenetic processes of biogeochemical calcium mineralization of primary organic matter as documented in more organized distributions with higher clustering.

Ultraviolet B‐induced alterations of the skin barrier and epidermal calcium gradient

Ultraviolet irradiation induces a variety of cutaneous changes, including epidermal permeability barrier disruption. In the present study, we assessed the effects of ultraviolet B (UVB) irradiation in epidermal barrier function and calcium distribution in murine epidermis. Adult hairless mice were exposed to a single dose of UVB (0.15 J/cm(2)). Barrier function was evaluated by transepidermal water loss (TEWL), lanthanum perfusion. The morphological alterations were examined by histology, immunohistochemistry and electron microscopy using ruthenium tetroxide (RuO(4)) postfixation. For evaluation of the effect on epidermal calcium distribution, the ion-capture cytochemistry was employed. UVB irradiation caused a significant increase in TEWL, which peaked at day 4. In parallel, the increased number of sunburn cells and the changes in epidermal hyperplasia and proliferation were observed. Electron microscopic observation demonstrated that the water-soluble lanthanum tracer was present in the extracellular stratum corneum domains, and the increased intercellular permeability was correlated with defective organization of the extracellular lipid lamellar bilayers of the stratum corneum. Moreover, UVB irradiation also caused an appearance of calcium precipitates in the stratum corneum and transitional cell layers as well as the increased cytosolic calcium in the lower epidermis, reflecting the alterations of the epidermal calcium gradient. These results suggest that the changes of the epidermal calcium distribution pattern may correlate with the perturbation of the epidermal barrier induced by UVB irradiation.

Distribution of calcium in peat deposits of the central part of Western Siberia

Distribution patterns of calcium in peat deposits of seventeen bogs in the middle and southern taiga of Western Siberia have been studied. Four types of Ca distribution patterns related to the genesis of peat deposits are specified. Up to three Ca-enriched peat layers are distinguished in thick deposits. This Ca distribution pattern is typical of different peat deposits formed under various conditions. It is shown that Ca accumulation in particular layers of peat deposits is related to the warm stages of the Holocene.

Endothelial nitric oxide synthase upregulation in the guinea pig organ of Corti after acute noise trauma

Endothelial nitric oxide synthase (eNOS) upregulation was identified 60 h after acute noise trauma in morphologically intact cells of the reticular lamina in the organ of Corti of the guinea pig in the second turn of the cochlea. Using gold-coupled anti-eNOS antibodies and electron microscopy, it was shown that eNOS expression was upregulated in all cell areas and cell types except inner hair cells. Furthermore, eNOS was found in the organelle-free cytoplasm and in mitochondria of various cell types. The density of eNOS in mitochondria was considerably higher compared with the surrounding cytoplasm. Since eNOS activity is regulated by calcium, the eNOS detection was combined with calcium precipitation, a method for visualizing intracellular Ca2+ distribution. After acute noise trauma, intracellular Ca2+ was increased in all cell types and cell areas except in outer hair cells. Comparing the distribution patterns of eNOS and calcium, significantly elevated levels (P < 0.0001) of eNOS were detected within a 100 nm radius near calcium precipitates in all cuticular structures as well as microtubule-rich regions and Deiters' cells near Hensen cells. The observed colocalization lends support to the postulated mechanism of eNOS activation by Ca2+. eNOS upregulation after acute noise trauma might therefore be part of an induced stress response. The eNOS upregulation in cell areas with numerous microtubule- and actin-rich structures is discussed with respect to possible cytoskeleton-dependent processes in eNOS regulation.

Spatiotemporal pattern of calmodulin and [Ca2+]i is related to resumption of meiosis in mouse oocytes.

During meiotic maturation, mammalian oocytes undergo a series of morphological and physiological changes that prepare them for fertilization. Calcium-initiated signaling is thought to trigger these processes. In this study, we examine the spatio-temporal pattern of calcium and calmodulin (CaM), its downstream receptor, in order to investigate their association with meiotic maturation. Intracellular free calcium and activated CaM levels were measured using the fluorescent probes Calcium Green-1 and TA-CaM, respectively. The distribution patterns were examined using confocal microscopy. Both calcium and activated CaM showed a dynamic spatiotemporal distribution during meiotic maturation. After release from IBMX buffer, calcium was found to periodically translocate from the perinuclear region to the germinal vesicle (GV) in 90 s intervals. After 90 min, calcium stopped oscillating and became concentrated within the GV. After a further 60 min, the GV broke down and calcium dispersed into the ooplasm, but calcium levels were slightly lower here than in the original nuclear region. Activated CaM also showed a dynamic patterning process similar to calcium. Taking the data from calcium chelation and CaM inhibition together, our results suggest that the dynamic distribution patterns of calcium and activated CaM are crucial for oocyte maturation.

Calcium handling by the cat carotid body - a pyroantimonate study

Subcellular regulation mechanisms of calcium concentrations related to oxygen sensing in the carotid body are unclear. In the present study, we investigated the ultrastructural distribution patterns of calcium in carotid body cells and its changes evoked by hypoxia. Carotid bodies were dissected from anesthetized cats exposed in vivo to normoxic or acute hypoxic conditions. We used the oxalate-pyroantimonate technique that yields an electron-opaque calcium precipitate. X-ray microanalysis and appropriate controls confirmed the presence of calcium in the precipitate. Calcium precipitates were found in all types of cells in carotid body parenchyma: chemoreceptor cells, sustentacular cells, and nerve endings. In normoxic chemoreceptor cells, the precipitate was localized in dense core vesicles, mitochondria, and nuclei, but rarely in the cytoplasm. The most apparent effect of hypoxia was disappearance of the precipitate from dense core vesicles and was associated with its appearance in the cytoplasm. The amount of precipitate throughout the carotid body parenchyma was decreased overall due to hypoxia. These results indicate the involvement of subcellular calcium trafficking in hypoxia-sensing in the carotid body. The redistribution pattern of granular calcium deposits from organelles to the cytoplasm of chemoreceptor cells agrees with biochemical data of calcium release from intracellular stores during hypoxia.