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  • 1
    Electronic Resource
    Electronic Resource
    Calmodulin binding to the intestinal brush-border membrane: Comparison to other calcium-binding proteins
    Amsterdam : Elsevier
    Biochimica et Biophysica Acta (BBA)/Molecular Cell Research 1010 (1989), S. 122-127 
    Details
    ISSN: 0167-4889
    Keywords: Brush-border membrane ; Calcium binding ; Calcium ion transport ; Calmodulin binding protein
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Medicine , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/0167-4889(89)90192-4
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Microtubules and pigment migration in the melanophores ofFundulus heteroclitus L. (1966)
    Springer
    Protoplasma 61 (1966), S. 322-345 
    Details
    ISSN: 1615-6102
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The dermal melanophores ofFundulus heteroclitus L. have been investigated by light and electron microscopy with the purpose of revealing the mechanisms controlling pigment migration. As predicted by earlier studies, the nerve endings of a double innervation were found adjacent to and in synaptic relation to the melanophore surface. Not expected were the large number of small pits or invaginations present in the cell surface. These appear identical to the so-called micropinocytotic vesicles found generally in cells of the vascular endothalium and smooth muscle. In chromatophores they are more reasonably interpreted as receptor sites for neurohormones than as uptake and transport mechanisms. Observations made on the kinetics of pigment migration within the processes of these melanophores indicate that the granules move along relatively fixed channels arranged parallel to the long axes of the processes. Examined at fine structure levels, the zones of cytoplasm around these channels are found to be populated by microtubules about 225 Å in diameter aligned parallel to the direction of pigment movement. These long slender elements are present in the processes regardless of whether the melanin is concentrated in the cell center or dispersed. It is reasoned from these and other observations that the microtubules function as cytoskeletal elements which help maintain the extended form of the melanophore arms and at the same time define the channels in which the pigment moves. The possible role of the tubule in generating the motive force for pigment migration is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01248988
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  • 3
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    The effect of 1,25-dihydroxyvitamin D-3 on the distribution of alkaline phosphatase activity along the chick intestinal villus (1977)
    Elsevier
    Details
    Publication Date: 1977-08-25
    Print ISSN: 0304-4165
    Electronic ISSN: 1872-8006
    Topics: Biology , Chemistry and Pharmacology , Medicine , Physics
    Published by Elsevier
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    PAPER CURRENT
  • 4
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    Skeletal unloading decreases production of 1,25-dihydroxyvitamin D (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The plasma concentration of 1,25-dihydroxyvitamin D [1,25(OH)2D] decreases during skeletal unloading and increases when normal weight bearing is restored. To determine whether these changes in plasma 1,25(OH)2D reflect changes in production, metabolic clearance, or both we measured the kinetics of 1,25(OH)2D metabolism in rats whose skeletons were normally loaded, unloaded, or reloaded after a period of nonweight bearing. Skeletal unloading produced a transient but striking fall in the production (-73%) and plasma concentration (-72%) of 1,25(OH)2D without having a significant effect (〈 20%) on metabolic clearance. Skeletal reloading returned production to normal. Bone formation predictably decreased during unloading and returned to normal after return to weight bearing. No consistent changes in blood ionized calcium, plasma immunoreactive parathyroid hormone (irPTH), or plasma phosphorus occurred. These data suggest that the changes in plasma 1,25-(OH)2D associated with changes in skeletal weight bearing primarily reflect changes in 1,25(OH)2D production. The data provide no evidence that the changes in 1,25(OH)2D production are a consequence of changes in blood ionized calcium, plasma irPTH, or phosphorus.
    Keywords: Life Sciences (General)
    Type: The American journal of physiology (ISSN 0002-9513); Volume 264; 5 Pt 1; E712-6
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  • 5
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    Altered skeletal pattern of gene expression in response to spaceflight and hindlimb elevation (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Spaceflight leads to osteopenia, in part by inhibiting bone formation. Using an animal model (hindlimb elevation) that simulates the weightlessness of spaceflight, we and others showed a reversible inhibition of bone formation and bone mineralization. In this study, we have measured the mRNA levels of insulin-like growth factor I (IGF-I), IGF-I receptor (IGF-IR), alkaline phosphatase, and osteocalcin in the tibiae of rats flown aboard National Aeronautics and Space Administration Shuttle Flight STS-54 and compared the results with those obtained from their ground-based controls and from the bones of hindlimb-elevated animals. Spaceflight and hindlimb elevation transiently increase the mRNA levels for IGF-I, IGF-IR, and alkaline phosphatase but decrease the mRNA levels for osteocalcin. The changes in osteocalcin and alkaline phosphatase mRNA levels are consistent with a shift toward decreased maturation, whereas the rise in IGF-I and IGF-IR mRNA levels may indicate a compensatory response to the fall in bone formation. We conclude that skeletal unloading during spaceflight or hindlimb elevation resets the pattern of gene expression in the osteoblast, giving it a less mature profile.
    Keywords: Aerospace Medicine
    Type: The American journal of physiology (ISSN 0002-9513); Volume 267; 6 Pt 1; E822-7
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  • 6
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    The molecular response of bone to growth hormone during skeletal unloading: regional differences (1995)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Hind limb elevation of the growing rat provides a good model for the skeletal changes that occur during space flight. In this model the bones of the forelimbs (normally loaded) are used as an internal control for the changes that occur in the unloaded bones of the hind limbs. Previous studies have shown that skeletal unloading of the hind limbs results in a transient reduction of bone formation in the tibia and femur, with no change in the humerus. This fall in bone formation is accompanied by a fall in serum osteocalcin (bone Gla protein, BGP) and bone BGP messenger RNA (mRNA) levels, but a rise in bone insulin-like growth factor-I (IGF-I) protein and mRNA levels and resistance to the skeletal growth-promoting actions of IGF-I. To determine whether skeletal unloading also induced resistance to GH, we evaluated the response of the femur and humerus of sham and hypophysectomized rats, control and hind limb elevated, to GH (two doses), measuring mRNA levels of IGF-I, BGP, rat bone alkaline phosphatase (RAP), and alpha 1(1)-procollagen (coll). Hypophysectomy (HPX) decreased the mRNA levels of IGF-I, BGP, and coll in the femur, but was either less effective or had the opposite effect in the humerus. GH at the higher dose (500 micrograms/day) restored these mRNA levels to or above the sham control values in the femur, but generally had little or no effect on the humerus. RAP mRNA levels were increased by HPX, especially in the femur. The lower dose of GH (50 micrograms/day) inhibited this rise in RAP, whereas the higher dose raised the mRNA levels and resulted in the appearance of additional transcripts not seen in controls. As for the other mRNAs, RAP mRNA in the humerus was less affected by HPX or GH than that in the femur. Hind limb elevation led to an increase in IGF-I, coll, and RAP mRNAs and a reduction in BGP mRNA in the femur and either had no effect or potentiated the response of these mRNAs to GH. We conclude that GH stimulates a number of markers of bone formation by raising their mRNA levels, and that skeletal unloading does not block this response, but the response varies substantially from bone to bone.
    Keywords: Aerospace Medicine
    Type: Endocrinology (ISSN 0013-7227); Volume 136; 5; 2099-109
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  • 7
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    Bone and hormonal changes induced by skeletal unloading in the mature male rat (1999)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: To determine whether the rat hindlimb elevation model can be used to study the effects of spaceflight and loss of gravitational loading on bone in the adult animal, and to examine the effects of age on bone responsiveness to mechanical loading, we studied 6-mo-old rats subjected to hindlimb elevation for up to 5 wk. Loss of weight bearing in the adult induced a mild hypercalcemia, diminished serum 1,25-dihydroxyvitamin D, decreased vertebral bone mass, and blunted the otherwise normal increase in femoral mass associated with bone maturation. Unloading decreased osteoblast numbers and reduced periosteal and cancellous bone formation but had no effect on bone resorption. Mineralizing surface, mineral apposition rate, and bone formation rate decreased during unloading. Our results demonstrate the utility of the adult rat hindlimb elevation model as a means of simulating the loss of gravitational loading on the skeleton, and they show that the effects of nonweight bearing are prolonged and have a greater relative effect on bone formation in the adult than in the young growing animal.
    Keywords: Aerospace Medicine
    Type: The American journal of physiology (ISSN 0002-9513); Volume 276; 1 Pt 1; E62-9
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  • 8
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    Space flight and the skeleton: lessons for the earthbound (1997)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Loss of bone during extended space flight has long been a concern that could limit the ability of humans to explore the universe. Surprisingly, the available data do not support the concept that weightlessness leads inexorably to a depleted skeleton unable to withstand the stress of a return to a 1-g environment. Nevertheless, some bone loss does occur, especially in those bones most stressed by gravity prior to flight, which provides confirmation of the proposal formulated over a century ago by Julius Wolff that mechanical stress determines the form and function of bone. Although the phenomenon of bone loss with skeletal unloading, whether by space flight or immobilization or just taking a load off your feet (literally) is well established, the mechanisms by which bone senses load and adjusts to it are not so clear. What actually is the stimulus, and what are the sensors? What are the target cells? How do the sensors communicate the message into the cells, and by what pathways do the cells respond? What is the role of endocrine, factors vs. paracrine or autocrine factors in mediating or modulating the response? None of these questions has been answered with certainty, but, as will become apparent in this review, we have some clues directing us to the answers. Although the focus of this review concerns space flight, it seems highly likely that the mechanisms mediating the transmission of mechanical load to changes in bone formation and resorption apply equally well to all forms of disuse osteoporosis and are likely to be the same mechanisms affected by other etiologies of osteoporosis.
    Keywords: Aerospace Medicine
    Type: The Endocrinologist (ISSN 1051-2144); Volume 7; 1; 10-22
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  • 9
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    Expression of the genes for insulin-like growth factors and their receptors in bone during skeletal growth (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Insulin-like growth factors (IGF) are important regulators of skeletal growth. To determine whether the capacity to produce and respond to these growth factors changes during skeletal development, we measured the protein and mRNA levels for IGF-I, IGF-II, and their receptors (IGF-IR and IGF-IIR, respectively) in the tibia and femur of rats before and up to 28 mo after birth. The mRNA levels remained high during fetal development but fell after birth, reaching a nadir by 3-6 wk. This fall was most pronounced for IGF-II and IGF-IIR mRNA and least pronounced for IGF-I mRNA. However, after 6 wk, both IGF-I and IGF-IR mRNA levels recovered toward the levels observed at birth. In the prenatal bones, the signals for the mRNAs of IGF-II and IGF-IIR were stronger than the signals for the mRNAs of IGF-I and IGF-IR, although the content of IGF-I was three- to fivefold greater than that of IGF-II. IGF-II levels fell postnatally, whereas the IGF-I content rose after birth such that the ratio IGF-I/IGF-II continued to increase with age. We conclude that, during development, rat bone changes its capacity to produce and respond to IGFs with a progressive trend toward the dominance of IGF-I.
    Keywords: Life Sciences (General)
    Type: The American journal of physiology (ISSN 0002-9513); Volume 267; 2 Pt 1; E278-86
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  • 10
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    Skeletal unloading induces selective resistance to the anabolic actions of growth hormone on bone (1995)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Loss of skeletal weight bearing or physical unloading of bone in the growing animal inhibits bone formation and induces a bone mineral deficit. To determine whether the inhibition of bone formation induced by skeletal unloading in the growing animal is a consequence of diminished sensitivity to growth hormone (GH) we studied the effects of skeletal unloading in young hypophysectomized rats treated with GH (0, 50, 500 micrograms/100 g body weight/day). Skeletal unloading reduced serum osteocalcin, impaired uptake of 3H-proline into bone, decreased proximal tibial mass, and diminished periosteal bone formation at the tibiofibular junction. When compared with animals receiving excipient alone, GH administration increased bone mass in all animals. The responses in serum osteocalcin, uptake of 3H-proline and 45Ca into the proximal tibia, and proximal tibial mass in non-weight bearing animals were equal to those in weight bearing animals. The responses in trabecular bone volume in the proximal tibia and bone formation at the tibiofibular junction to GH, however, were reduced significantly by skeletal unloading. Bone unloading prevented completely the increase in metaphyseal trabecular bone normally induced by GH and severely dampened the stimulatory effect (158% vs. 313%, p 〈 0.002) of GH on periosteal bone formation. These results suggest that while GH can stimulate the overall accumulation of bone mineral in both weight bearing and non-weight bearing animals, skeletal unloading selectively impairs the response of trabecular bone and periosteal bone formation to the anabolic actions of GH.
    Keywords: Aerospace Medicine
    Type: Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research (ISSN 0884-0431); Volume 10; 8; 1168-76
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