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  • 1
    Electronic Resource
    Electronic Resource
    Ultrastructural and microanalytical aspects of developing osteodentin in rat incisors (1977)
    Springer
    Calcified tissue international 24 (1977), S. 215-222 
    Details
    ISSN: 1432-0827
    Keywords: Mineralization ; Osteodentin ; Intracellular ; Ultrastructure ; Microanalysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Newly formed osteodentin obtained from the anterior extremities of fetal or young rat incisors was observed by means of electron microscopy and electron probe X-ray microanalysis. Cells related to osteodentin formation frequently showed membrane bound intracellular bodies containing varying amounts of fine, needle-shaped crystals, which were identified as apatite. The intracellular clusters of apatite crystals were extruded from the cells through membrane fusion or cellular degeneration. These extracellular clusters seemed to be gradually incorporated into the mineralizing collagenous matrix, which developed around them. Frequent occurrence of dense, dotshaped or filamentous profiles suggested that the dense bodies seen in the perinuclear regions or in the Golgi area were the sites of crystal formation. Energy dispersive X-ray point analysis showed that the intracellular or extracellular apatite clusters contained sulfur in a concentration higher than was present in the mineralizing collagenous matrix. Furthermore, wave dispersive X-ray line analysis showed that the concentration of sulfur was higher in the osteodentin matrix than in the dentin matrix. The sulfur detected is presumed to be contained in acid mucopolysaccharides, which were distributed more heavily in the osteodentin matrix than in the dentin matrix. On the basis of these data, it was concluded that the unique chemical and structural characteristics of the osteodentin result primarily from the incorporation of apatite clusters of intracellular origin and associated acid mucopolysaccharides.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02223319
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    The role of vitamin D in the mineralization of dentin in rats made rachitic by a diet low in calcium and deficient in vitamin D (1974)
    Springer
    Calcified tissue international 15 (1974), S. 295-302 
    Details
    ISSN: 1432-0827
    Keywords: Vitamin D ; Mineralization ; Dentin ; Rickets
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract A study was undertaken to ascertain whether vitamin D has a direct action on the mineralization of the dentin in rats made rachitic by a diet low in calcium and deficient in vitamin D. Physiological amounts of vitamin D, given orally to rachitic rats, increased their serum calcium from 4.8±0.5 mg/100 ml to 7.5±0.4 mg/100ml. The mineralization of dentin recovered markedly, although osteoporosis occurred in bone trabeculae. The results suggest that vitamin D increases serum calcium by accelerating bone resorption and that the increased serum calcium level acts directly to mineralize the dentin. When calcium was given to rachitic rats by subcutaneous injection, the serum calcium level increased and mineralization of dentin recovered to the same extent as that observed in rats given vitamin D. These results indicate that recovery of mineralization of rachitic dentin depends primarily on recovery of the serum calcium level and that vitamin D is an indirect factor in the mineralization process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02059064
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Positive inotropic effect of 4-aminopyridine on dog ventricular muscle (1979)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 307 (1979), S. 207-212 
    Details
    ISSN: 1432-1912
    Keywords: 4-Aminopyridine ; Cardiac muscle ; Relaxation ; Action potential ; Catecholamines ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary 1. In trabecular muscles obtained from the right ventricle of untreated dogs 4-aminopyridine (4-AP) (0.1–10 mM) increased the force of contraction elicited by electrical driving at 0.5 Hz. 2. This effect was associated with increases in mean velocities of force development and relaxation. The time to peak force was not changed by 4-AP and the relaxation time was increased by 3 and 10 mM 4-AP. 3. In ventricular muscles treated with the β-adrenoceptor blocking agent, pindolol, or in those obtained from dogs pretreated with reserpine the positive inotropic effect was reduced. 4. In such muscles 4-AP scarcely increased the mean velocity of force development and slightly increased the time to peak force. Marked prolongation of the relaxation time and a decrease in mean velocity of relaxation were characteristic of isometric contractions of such muscles in the presence of 4-AP. 5. These results indicate that the positive inotropic effect of 4-AP is sum of two effects, one being due to the release of endogenous catecholamines and the other to a possible direct action on cardiac muscle. 6. In muscles treated with pindolol or those obtained from dogs pretreated with reserpine 10 mM 4-AP elevated the resting force. 7. These observations suggest that 4-AP causes a persisting elevation of cytosolic Ca2+ in cardiac muscle cells. 8. In pindolol-treated muscles 4-AP prolonged the action potential duration. However, the prolongation of the action potential duration produced by 4-AP was much smaller than that of the relaxation time. Even with 10 mM 4-AP the resting membrane potential remained unchanged. 9. The above results suggest that the effects of 4-AP on the contraction and resting force of ventricular muscle may not be secondary to the effect on the transmembrane potential. 10. All the results taken together suggest that the primary action of 4-AP on ventricular muscle may not be to allow increased or prolonged entry of extracellular Ca2+ but rather may be either to promote the release of Ca2+ from intracellular binding or storage sites or to slow the binding of Ca2+ to intracellular structures. The prolongation of the action potential duration may be a consequence of change in calcium binding to the plasma membrane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00505935
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    Paper (German National Licenses)
    Fulltext
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