Distribution Of Alkaline Phosphatase Activity Research Articles

The spatio-temporal distribution of alkaline phosphatase activity and phoD gene abundance and diversity in sediment of Sancha Lake

The bacterial phoD gene encoding alkaline phosphatase (ALP) plays an important role in the release of soluble reactive phosphorus (SRP) from organic phosphorus in ecosystems. However, phoD gene diversity and abundance in ecosystems is poorly understood. In the present study, we sampled the surface sediments and the overlying water of Sancha Lake at 9 different sampling sites, a typical eutrophic sub-deep freshwater lake in China, in April 15 (spring) and November 3 (autumn), 2017. High-throughput sequencing and qPCR were performed to analyze the diversity and abundance of the bacterial phoD gene in the sediments. We further discussed the relationships between the diversity and abundance of the phoD gene and environmental factors and ALP activity. A total of 881,717 valid sequences were obtained from 18 samples and were classified into 41 genera, 31 families, 23 orders, 12 classes, and 9 phyla and grouped into 477 OTUs. The dominant phyla were Proteobacteria and Actinobacteria. The phylogenetic tree based on the sequences of the phoD gene was plotted and composed of three branches. The genetic sequences were aligned predominantly with genera Pseudomonas, Streptomyces, Cupriavidus, and Paludisphaer. The phoD-harboring bacterial community structure showed a significant difference in spring and autumn, but no apparent spatial heterogeneity. The phoD gene abundances at different sampling points were significantly higher in autumn than in spring. In autumn and spring, the phoD gene abundance was significantly higher in the tail of lake and where cage culture used to be intensive. pH value, dissolved oxygen (DO), total organic carbon (TOC), ALP, and phosphorus were important environmental factors affecting the diversity of the phoD gene and the phoD-harboring bacterial community structure. Changes in phoD-harboring bacterial community structure, phoD gene abundance, and ALP activity were negatively correlated with SRP in overlying water. Our study indicated phoD-harboring bacteria in the sediments of Sancha Lake with the characteristics of high diversity and significant spatial and temporal heterogeneity in abundance and community structure, which played a important role in the release of SRP.

Phytoplankton communities determine the spatio-temporal heterogeneity of alkaline phosphatase activity: evidence from a tributary of the Three Gorges Reservoir

In order to reveal the role of phytoplankton in the spatio-temporal distribution of alkaline phosphatase activity (APA), monthly investigations were conducted in the Xiaojiang River, a tributary of the Three Gorges Reservoir in China. Different APA fractions, environmental parameters, and phytoplankton communities were followed. High spatio-temporal variations of APA were observed, with the highest value in summer and the lowest in winter. The annual average APAT (total alkaline phosphatase activity) ranged from 7.78–14.03 nmol∙L−1∙min−1 with the highest in the midstream and the lowest in the estuary. The dominant phytoplankton phyla in summer and winter were Cyanophyta and Bacillariophyta, respectively. The mean cell density in the midstream and in the estuary was 5.2 × 107 cell∙L−1 and 1.4 × 107 cell∙L−1, respectively. That APA>3.0 μm was significantly higher than APA0.45-3 μm indicating phytoplankton was the main contributor to alkaline phosphatase. Correlation analysis indicated the dominant species and cell density could determine the distribution pattern of APA. Turbidity, total phosphorus, chemical oxygen demand, water temperature (WT), pH and chlorophyll a were proved to be positively correlated with APA; soluble reactive phosphorus, conductivity, transparency and water level(WL) were negatively correlated with APA. It was concluded that spatio-temporal heterogeneity of APA determined by phytoplankton communities was related to WT and WL.

Variations of alkaline phosphatase activity and P fractions in sediments of a shallow Chinese eutrophic lake (Lake Taihu)

The distribution of alkaline phosphatase activity (APA) and P fractions in sediment cores and the relationship between them were studied in a shallow Chinese freshwater lake (Lake Taihu). Sediment cores were collected from four sites, characterized by different degrees of eutrophication in June 2004. Sediment P was fractionated into Fe/Al-P, Ca-P, organic P (OP), inorganic P (IP) and total P (TP). The former two species made the largest contribution to the sediment P pool. Results show that trophic status and hydrological conditions have great impact on the APA of the sediments. The order of the APA in sediments was conjectured to be: macrophyte dominated lake > transitional lake > algal dominated lake. APA profiles follow a similar downcore decreasing trend. There was a positive relationship between the APA and the TP, IP. The multiple linear regression equation of the APA and P fractions is: APA = −97 + 0.768TP − 0.985Fe/Al-P.

Towards Defining the Pathogenesis of the Hairless Phenotype

Mutation of the hairless (hr) gene in mice causes severe abnormalities during the first hair follicle regression (catagen), resulting in complete baldness. Here, we further characterize how hairlessness develops in HRS/J hairless mouse skin (hr) by histology, histochemistry, immunohistology, and in situ hybridization. We show that, in hr skin, only two defined epithelial cell populations in the distal outer root sheath (ORS) retain their integrity, whereas the rest of the ORS disintegrates. The surviving distal ORS forms the characteristic utriculi, whereas the remnants of the bulge get isolated from other epithelial compartments, but retain the capacity to proliferate and to produce either columnar epithelial outgrowths or selected dermal cysts. Normal dermal papilla structures get lost during the development of hairlessness. Based on the patterns of keratin 17 mRNA and neural cell adhesion molecule antigen expression, and on the distribution of alkaline phosphatase activity, we propose that dermal cysts in hr skin arise from (i) the central ORS, (ii) bulge-derived cells, or (iii) the disintegrating proximal ORS under the influence of dermal papilla remnants. The hr mutation seems to disrupt the integrity of key functional tissue units in the hair follicle, possibly due to a dysregulation of normal, catagen-associated apoptosis and/or an impairment of cell adhesion, whereas the distal follicle epithelium (including its stem cell region) seems to be largely protected from this. Thus, hairless mice offer a unique model for dissecting the as yet obscure functional properties of the hr gene product in maintaining follicle integrity during normal catagen.

Temporal and spatial distribution of alkaline phosphatase activity in male hypogonadic rat (hgn/hgn) testis during postnatal development.

In male hypogonadic mutant rat (hgn/hgn), gonocytes degenerate and peritubular cells form multiple layers around seminiferous tubules during early postnatal testicular development. Alkaline phosphatase (AP) activity has been used as not only a tracer for the primordial germ cells (PGCs) but also a histochemical marker for the peritubular myoid cells. In the present study, we examined the localization of AP activity during the postnatal testicular development in the hgn/hgn and phenotypically normal (+/+ or +/hgn) rat. In the normal testis, high AP activity was located in the surface of the PGCs on 3 days of age. As the PGCs differentiated into spermatogonia, the AP activity drastically decreased in intensity on 7 days and was completely lost by 12 days. In the hgn/hgn, the PGCs showing high AP activity occupied the inside of dilated seminiferous tubules on 3 and 7 days of age. The luminal AP activity declined gradually by 18 days and disappeared on 21 days, when the germ cells completely degenerated in the hgn/hgn testis. In the normal, high AP activity emerged in a layer of the peritubular cells surrounding the tubules on 7 days and afterwards, indicating that the peritubular cells were differentiating into myoid cells. In the hgn/hgn, the peritubular cells formed multiple layers around the tubules and showed weak AP activity on 3 to 18 days of age. On 21 days of age, high AP activity emerged in a single layer of the peritubular cells directly attached to the basement membrane in the hgn/hgn. These results indicate that the PGCs showing AP activity kept remained at later stage in the hgn/ hgn and that the single layer of mature myoid cells showing high AP activity appeared much later in the hgn/hgn testis than in normal.

Effect of clinostat rotation on differentiation of embryonic bone in vitro

We have investigated the effect of changes in the gravity vector on osteoblast behaviour, using the clinostat set at 8 rpm. Two sources of osteoblasts were used: secondary cultures of fetal rat bone cells, and the rat osteosarcoma line 17/2.8 (ROS). Cell number was determined by incubation with 3-(4,dimethyl-2yl)-2,3 diphenyl) tetrazolium bromide (MTT) and measurement of optical density at 570 nm (OD). Alkaline phosphatase activity was detected by standard cytochemical methods. Dividing cells were localised by labelling dividing nuclei with Bromodeoxyuridine (BrdU), detected by immunofluorescence. Cell culture was initiated at densities between 1–4×10 4 cells ml −1. Growth rates in all cultures during the first 48 hours exposure to clinostat rotation were less than in stationary controls. After 3 days, ROS cell numbers were 35% lower, and calvarial cells 39% lower than their respective controls. Alkaline phosphatase activity in calvarial control cultures was uniformly present in characteristically polygonal cells, but after culture in the clinostat the enzyme was present sporadically, and the cells were cuboid. There was also no BrdU uptake in nuclei, but it was present in cell cytoplasms. We conclude that the clinostat decreases cell numbers and cell division. Both cell shape and the distribution of alkaline phosphatase activity in calvarial cell cultures were also affected. This implies that changes in the gravity vector can affect osteoblasts directly, without interaction with other cell types.

Dynamic reorganization of the alkaline phosphatase-containing compartment during chemotactic peptide stimulation of human neutrophils imaged by backscattered electrons.

Scanning electron microscopy (EM) and cytochemical techniques were used to examine the alkaline phosphatase-containing compartment in human neutrophils after stimulation with nanomolar concentrations of N-formylmethionyl-leucyl-phenylalanine (10(-8) M fMLP). Alkaline phosphatase (AlkPase) activity was demonstrated with a lead-based metal capture cytochemical method. The reaction product was visualized with the backscattered electron imaging mode of scanning EM, and analyzed by electron probe X-ray microanalysis. Alkaline phosphatase activity was detected only in fMLP-stimulated neutrophils; unstimulated neutrophils displayed no activity. Stimulation of human neutrophils with 10(-8) M fMLP induced a time-dependent intracellular redistribution of irregular round or tubular granules containing alkaline phosphatase activity, as seen by backscattering. The intracellular redistribution of alkaline phosphatase activity was accompanied by increased cytochemical activity on the cell surface. The reaction product was localized preferentially on ridges and folds of polar neutrophils. Reorganization of the AlkPase-containing compartment correlated with changes induced by fMLP in cell shape, ie, membrane ruffling and front-tail polarity, as observed with the secondary electron image mode of scanning EM. These findings demonstrate the intracellular reorganization, increase, and asymmetric distribution of alkaline phosphatase activity on the plasma membrane of human neutrophils after stimulation by chemotactic peptides.

Localization and distribution of alkaline phosphatase activity in the hepatopancreas of the snail

Histocytochemical methods were used to investigate alkaline phosphatase activity in the digestive gland (hepatopancreas) of the common garden snail Helix aspersa. Histochemical findings and light microscopic observations showed that enzymatic activity was confined mainly to the basal connective tissue that enveloped the adenomeres. Transmission electron microscopy showed that enzymatic activity was localized in the plasma membrane, and showed an intercellular distribution along the lateral surfaces and the basal portions of the cells in different adenomeres. Alkaline phosphatase activity was also found in the plasma membrane of fibrocytes of the basal connective tissue enveloping the adenomeres. Enzymatic activity was seen around the fat droplets of glandular cells. The possible involvement of alkaline phosphatase in processes or remodelling of the basal connective tissue that envelopes the gland is discussed.

A quantitative enzyme histochemical analysis of the distribution of alkaline phosphatase activity in the periodontal ligament of the rat incisor.

The spatial distribution of alkaline phosphatase (ALP) activity was examined in the periodontal ligament of the continuously growing rat incisor. With the indoxyl-tetrazolium salt method, enzyme activity was demonstrated in undecalcified cryosections, and the amount of reaction product was quantified. ALP activity appeared to be distributed heterogeneously. Its highest activity was found in the bone-related compartment of the ligament. In the tooth-related compartment and the supracrestal extension of the ligament, enzyme activity was significantly lower, but still higher than in the lamina propria of the gingiva. In the part of the ligament bordering the cementum, highest activity was found in the apical region just occlusal to Hertwig's epithelial root sheath, where formation of acellular cementum begins. From there toward the incisal edge, the activity of the enzyme gradually decreased. It is suggested that differences among the various parts of the periodontal ligament are related to local variations in phosphate metabolism and cementum deposition.

Increased matrix vesicle protein in rachitic rat epiphyseal growth plates

Extracellular, membrane-bound vesicles are widely regarded to be the initial site of calcification in a variety of tissues under normal and pathological conditions. Alkaline phosphatase is believed to play a vital role in this process by hydrolysing ester phosphates or mineral inhibitors, e.g. inorganic phosphates. In the present study, matrix vesicles from normal and rachitic rat growth plates were compared with regard to specific activity of alkaline phosphatase, total vesicle protein and ultrastructural distribution of alkaline phosphatase activity. Matrix vesicles were released from normal or rachitic growth plates by collagenase digestion and isolated by differential centrifugation. Enzyme cytochemical localization involving a cerium capture method was performed on vesicles collected by vacuum filtration on Millipore filters. SDS gels and Western blots on fractions of both normal and rachitic matrix vesicles showed major proteins to be almost identical and confirmed the presence of alkaline phosphatase in both. Total matrix vesicle protein ((mg total matrix vesicle protein/rat) × 10 2) per rat was significantly greater for the rachitic animals (9.0 ± 2.0 vs. 4.0 ± 1.0), P < 0.0001. Alkaline phosphatase specific activity (units alkaline phosphatase/mg vesicle protein) in the rachitic and normal matrix vesicles was 25.29 ± 9.36 and 18.78 ± 3.37, respectively (0.05 < P < 0.1). Electron dense cerium phosphate deposits were localized to the outer membrane surface of matrix vesicles derived from both types of rats. This data, the first to quantify the relationship between rickets, matrix vesicle protein and alkaline phosphatase specific activity, suggests that matrix vesicles from rachitic and normal rats have biochemical and morphological similarity. Since the quantity of vesicle protein released from rachitic growth plates is 2–3 times greater per animal than that released from normals, the induction of rickets represents an approach by which matrix vesicle yield can be significantly increased.

Spontaneous Lipolysis in Bovine Milk: Combined Effects of Nine Characteristics in Native Milk

Relationships between spontaneous lipolysis and several intrinsic characteristics of native milk were studied in a total of 210 milks. Whole milk lipase activity, distribution of alkaline phosphatase activity in cream and skim milk, milk pH, fat and protein content, and SCC were not related to spontaneous lipolysis. The FFA development was partially related to LPL associated with the cream (r = .41, n = 116) and to the susceptibility of the fat to Candida cylindracea lipase (r = .57; n = 109). The higher correlation coefficient was observed between spontaneous lipolysis and activator-inhibitor balance in skim milk (r = .69. n = 89). Simultaneous measurement of these characteristics in 52 samples showed that a lower content of inhibitors in skim milk was linked to a higher susceptibility of the correspondent fat to exogenous Candida cylindracea lipase as well as to a higher amount of cream LPL.

Ultrastructural localisation of alkaline phosphatase activity in osteoarthritic human articular cartilage.

The distribution of alkaline phosphatase activity in human articular cartilage from normal and osteoarthritic joints has been examined by an electron microscope technique, probably for the first time. In osteoarthritic cartilage chondrocytes and matrix vesicles close to the tidemark were positive for alkaline phosphatase activity. Large numbers of matrix vesicles were found within the extracellular matrix of osteoarthritic cartilage, and there is a specific relation between phosphatase activity, matrix vesicles, and initial mineral formation in the tidemark region of articular cartilage.

Distribution of alkaline phosphatase activity in experimentally produced callus in rats.

Experimentally produced fractures in long bones studied by light and electron microscopic histochemistry were found to heal by a process of enchondral calcification. There was intense proliferation in the cells of the cambium layer of the periosteum, with differentiation to chondroblasts and osteoblasts, suggesting that this layer was the primary tissue responsible for development of the callus. Cytoplasmic processes of the hypertrophic chondrocytes appeared to bud and produce matrix vesicles. Alkaline phosphatase activity was detected along the plasma membrane of the hypertrophic chondrocytes and around the matrix vesicles, before any signs of mineral deposition. Calcification took place by deposition of hydroxyapatite crystals in and around these matrix vesicles which frequently showed alkaline phosphatase activity. It is suggested that there is a close functional association between alkaline phosphatase activity and calcification in the process of fracture healing, which is another type of enchondral calcification mediated by matrix vesicles.

Schistosoma mansoni: Radioautography of colchicine's effect on [ 3H]proline incorporation into adults in vitro

Adult Schistosoma mansoni were studied radioautographically in order to ascertain the effect of exposures to a fixed concentration of colchicine (5 × 10 −4 M) for varying time intervals upon the incorporation of [ 3H]proline in the tegument. Additionally, a study was made on the effect of varying time exposures of colchicine on the cytochemical localization of alkaline phosphatase (EC 3.1.3.1) in the tegumental invaginations. Worms exposed to colchicine for more than 2 hr preceding addition of the labeled amino acid displayed significant changes in the pattern of distribution. The most profound change was noted in the male tegument where a statistically significant decrease was observed in treated worms. Female worms, on the other hand, failed to display any effect of the drug on the distribution pattern for the times utilized. The distribution of alkaline phosphatase activity was much reduced in the teguments of both sexes. Morphological effects of the drug included disappearance of microtubules from the cytoplasmic connectives, a stacking of RER in the subtegumental cells, and accumulation of discoid granules and membranous bodies in the subtegumental cells. It is hypothesized that the amino acid is associated with the discoid granule at the subtegumental cell level and is ultimately translocated, with the aid of microtubules in the cytoplasmic connectives, to the tegument. Alkaline phosphatase activity is assumed to be associated with the membranous body.

Distribution of 99mTc-phosphate compounds in osteoarthritic femoral heads.

In a study of the distribution of 99mTc-polyphosphate and 99mTc-methylene diphosphonate in osteoarthritic femoral heads by macroautoradiography of samples obtained during replacement surgery, the bone-seeking agents were seen to accumulate in the weight-bearing, denuded areas, mainly in the cyst walls and at the osteochondral junctions in the osteophytes. The autoradiographic findings were substantiated by findings from impulse-counting of different zones in the femoral heads that were done on frozen sections. Morphological studies of sections adjacent to the cut surface used for autoradiography showed that the accumulations of the radionuclides were located in areas of new-bone formation, particularly enchondral ossification. This finding was confirmed by histochemical staining for alkaline phosphatase, a marker enzyme for bone mineralization. The over-all distribution of alkaline phosphatase activity in cells roughly paralleled the deposition of the bone-seeking agents. Scintigrams of osteoarthritic joints reflect primarily the rate of osteogenesis in subchondral bone and osteophytes. As the scan is positive even in very early stages in the development of the disease, a more detailed knowledge of the mechanism responsible for an increased uptake of 99mTc-phosphate compounds may, among other things, contribute to the elucidation of the pathogenesis.

The distribution of alkaline phosphatase activity in normal and cross-species regenerated rat and mouse taste buds.

Alkaline phosphatase (ALK Pase) activity can be detected histochemically in the taste buds of rats but not mice. Since taste buds develop, regenerate and are maintained under the influence(s) of the sensory nerve it was decided to study cross-species regenerated buds of these two animals to determine whether the nerve also regulated ALK Pase development in taste cells. Grafts of rats sensory ganglion and mouse tongue or mouse ganglion and rat tongue were combined in the anterior chamber of the eyes of immunologically-deficient nude mice and the cross-species buds that developed at 35 days were examined histochemically for ALK Pase. The results revealed that the rat nerve did not cause ALK Pase to appear in any buds found in mouse tongue grafts and that mouse nerve could support buds containing ALK Pase in rat tongue tissue. Because the cross-species regenerated buds were histochemically characteristic of those normally found in rat or mouse tongue, there is no evidence that the foreign nerve altered gene expression for ALK Pase in the target organ, and the action of the nerve on gustatory epithelium appears to be that of activation and maintenance.

Histochemical study of the amphibian digestive tract during normal and thyroxine‐induced metamorphosis. I. Alkaline phosphatase

AbstractHistochemical patterns of alkaline phosphatase activity were demonstrated in specific regions of the digestive tube in a series of growing and metamorphosing larvae and frogs of Rana pipiens. In growing larvae activity in the mucosal epithelium was intense and sharply localized in the striated border of the duodenum posterior to the bile duct and of the mid‐small intestine. No activity was found in the epithelial lining of the esophagus, stomach (or its glands), duodenum anterior to the bile duct, end of small intestine, or large intestine. Connective tissue and blood vessels throughout the length of the digestive tract displayed moderate activity. As remodeling of the gut began in metamorphosing larvae, the high phosphatase activity in the striated border decreased sharply, but activity in the connective tissue of the entire digestive tract increased substantially. As metamorphosis neared completion and a new mucosal epithelium developed, activity became strong in the striated border throughout the small intestine, including the region anterior to the bile duct and the end‐small intestine. In adult well‐fed frogs activity remained in this location, although in unfed frogs kept in the cold it diminished in the striated border and became prominent in subepithelial blood vessels. Enzyme activity was not detected in connective tissue (excepting random blood vessels) in any region of the frog digestive tract. These histochemical observations represent an overview of the distribution of alkaline phosphatase activity along the length of the digestive tract during larval and adult stages of a single anuran species.

The effect of 1,25-dihydroxyvitamin D-3 on the distribution of alkaline phosphatase activity along the chick intestinal villus

Rachitic chicks received 2.5 nmol of 1,25-dihydroxyvitamin D-3 (1,25(OH) 2D 3) at 4, 8, 12, 24 and 48 h, respectively, before killing. A small piece of the duodenum from each chick was frozen and divided into two parts. One part was serially sectioned perpendicular to the longitudinal axis of the villi. Each section was analyzed for alkaline phosphatase and sucrase activities. The second part was sectioned parallel to the longitudinal axis of the villus to determine villar length by morphometry. The results indicate that: 1. 1. A gradient of alkaline phosphatase activity exists along the villus with maximal activity at the tip. 2. 2. 1,25(OH) 2D 3 stimulated alkaline phosphatase activity along the entire length of the villus. The responses of different regions of the villus to 1,25(OH) 2D 3 were parallel in time for the first 12–24 h indicating a lack of differential response according to cell age. By 48 h the alkaline phosphatase activity at the base of the villus had returned to control values whereas the activity at the tip of the villus remained fully stimulated. 3. 3. A significant increase in villar length was observed in the duodenal specimens from the 1,25(OH) 2D 3-treated chicks. 4. 4. Sucrase activity does not parallel alkaline phosphatase activity but is greater in the region just distal to the crypts with little activity at the villar tip or in the bottom of the crypts. 5. 5. 1,25(OH) 2D 3 had no significant effect on the amount or distribution of sucrose activity.

Uneven distribution of alkaline phosphatase in individual layers of rabbit and ox cornea. Histochemical and biochemical study.

In the rabbit and bovine cornea the activity of alkaline phosphatase using histochemical as well as biochemical methods was investigated. Biochemically the enzyme activity was studied in separated corneal layers. In the histochemical investigation the best results were obtained in cryostat sections using the azocoupling method with naphthol AS-MX phosphate and Variamine Blue RT Salt. The enzyme activity was found not only in the epithelium and endothelium (as was described previously) but even in keratocytes. The mutual relation of activities in the epithelium and in keratocytes differed in both species. The overall activity found by histochemical methods is in good agreement with the biochemical determination of alkaline phosphatase (p-nitrophenyl phosphate as the substrate). Besides the histochemical approach shows an uneven distribution of alkaline phosphatase activity in individual cells which cannot be assessed by the biochemical determination.

Electron microscopie and enzyme cytochemical studies on the guinia pig metaphysis with special reference to the lysosomal system of different cell types.

A transmission electron microscopic study of demineralized, methaphyseal bone of the young guinea pig is presented. Special attention is paid to the lysosomal system of the different cell types. Visualization of acid phosphatase and aryl sulfatase activity was used to identify tissue components as belonging thereto. The distribution of alkaline phosphatase activity, a plasma membrane marker, was also examined. Osteoblasts were distinguished by a marked development of the granular endoplasmic reticulum and the Golgi complex. Perivascular cells type A, morphologically resembled the osteoblasts, and are believed to represent an early stage in the specialization of the latter. A few lysosomes were normally found in the osteoblasts; they were less common in the type A cells. In contrasts to their regular occurrence in guinea pig epiphyseal cartilage, dense bodies of lysosomal nature ("type I vesicles") were only rarely seen in the bone matrix. Structures analogous to the type II vesicles in cartilage were, however, normally present. Their membrane showed activity of alkaline phosphatase. Possible functions of lysosomes and matrix vesicles in osteogenesis are discussed. Perivascular cells type B and chondroclasts both contained a prominent Golgi complex and large numbers of free ribosomes, mitochondria and lysosomes. In the type B cells, inclusion material of varying appearance often occurred in the lysosomes and in endocytic vesicles. The chondroclasts sometimes presented a ruffled border, with associated vacuoles and lysosomes in the subjacent cytoplasm. It is suggested that both cell types participate in the resorption of the epiphyseal cartilage. Chondroclasts presumably arise by fusion of type B cells and/or monocytic precursors from the peripheral blood.